1.\"- 2.\" Copyright (c) 1991, 1993 3.\" The Regents of the University of California. All rights reserved. 4.\" 5.\" This code is derived from software contributed to Berkeley by 6.\" Kenneth Almquist. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 3. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" from: @(#)sh.1 8.6 (Berkeley) 5/4/95 33.\" $FreeBSD$ 34.\" 35.Dd April 18, 2015 36.Dt SH 1 37.Os 38.Sh NAME 39.Nm sh 40.Nd command interpreter (shell) 41.Sh SYNOPSIS 42.Nm 43.Op Fl /+abCEefhIimnPpTuVvx 44.Op Fl /+o Ar longname 45.Oo 46.Ar script 47.Op Ar arg ... 48.Oc 49.Nm 50.Op Fl /+abCEefhIimnPpTuVvx 51.Op Fl /+o Ar longname 52.Fl c Ar string 53.Oo 54.Ar name 55.Op Ar arg ... 56.Oc 57.Nm 58.Op Fl /+abCEefhIimnPpTuVvx 59.Op Fl /+o Ar longname 60.Fl s 61.Op Ar arg ... 62.Sh DESCRIPTION 63The 64.Nm 65utility is the standard command interpreter for the system. 66The current version of 67.Nm 68is close to the 69.St -p1003.1 70specification for the shell. 71It only supports features 72designated by 73.Tn POSIX , 74plus a few Berkeley extensions. 75This man page is not intended to be a tutorial nor a complete 76specification of the shell. 77.Ss Overview 78The shell is a command that reads lines from 79either a file or the terminal, interprets them, and 80generally executes other commands. 81It is the program that is started when a user logs into the system, 82although a user can select a different shell with the 83.Xr chsh 1 84command. 85The shell 86implements a language that has flow control constructs, 87a macro facility that provides a variety of features in 88addition to data storage, along with built-in history and line 89editing capabilities. 90It incorporates many features to 91aid interactive use and has the advantage that the interpretative 92language is common to both interactive and non-interactive 93use (shell scripts). 94That is, commands can be typed directly 95to the running shell or can be put into a file, 96which can be executed directly by the shell. 97.Ss Invocation 98.\" 99.\" XXX This next sentence is incredibly confusing. 100.\" 101If no arguments are present and if the standard input of the shell 102is connected to a terminal 103(or if the 104.Fl i 105option is set), 106the shell is considered an interactive shell. 107An interactive shell 108generally prompts before each command and handles programming 109and command errors differently (as described below). 110When first starting, the shell inspects argument 0, and 111if it begins with a dash 112.Pq Ql - , 113the shell is also considered a login shell. 114This is normally done automatically by the system 115when the user first logs in. 116A login shell first reads commands 117from the files 118.Pa /etc/profile 119and then 120.Pa .profile 121in a user's home directory, 122if they exist. 123If the environment variable 124.Ev ENV 125is set on entry to a shell, or is set in the 126.Pa .profile 127of a login shell, the shell then subjects its value to parameter expansion 128and arithmetic expansion and reads commands from the named file. 129Therefore, a user should place commands that are to be executed only 130at login time in the 131.Pa .profile 132file, and commands that are executed for every shell inside the 133.Ev ENV 134file. 135The user can set the 136.Ev ENV 137variable to some file by placing the following line in the file 138.Pa .profile 139in the home directory, 140substituting for 141.Pa .shrc 142the filename desired: 143.Pp 144.Dl "ENV=$HOME/.shrc; export ENV" 145.Pp 146The first non-option argument specified on the command line 147will be treated as the 148name of a file from which to read commands (a shell script), and 149the remaining arguments are set as the positional parameters 150of the shell 151.Li ( $1 , $2 , 152etc.). 153Otherwise, the shell reads commands 154from its standard input. 155.Pp 156Unlike older versions of 157.Nm 158the 159.Ev ENV 160script is only sourced on invocation of interactive shells. 161This 162closes a well-known, and sometimes easily exploitable security 163hole related to poorly thought out 164.Ev ENV 165scripts. 166.Ss Argument List Processing 167All of the single letter options to 168.Nm 169have a corresponding long name, 170with the exception of 171.Fl c 172and 173.Fl /+o . 174These long names are provided next to the single letter options 175in the descriptions below. 176The long name for an option may be specified as an argument to the 177.Fl /+o 178option of 179.Nm . 180Once the shell is running, 181the long name for an option may be specified as an argument to the 182.Fl /+o 183option of the 184.Ic set 185built-in command 186(described later in the section called 187.Sx Built-in Commands ) . 188Introducing an option with a dash 189.Pq Ql - 190enables the option, 191while using a plus 192.Pq Ql + 193disables the option. 194A 195.Dq Li -- 196or plain 197.Ql - 198will stop option processing and will force the remaining 199words on the command line to be treated as arguments. 200The 201.Fl /+o 202and 203.Fl c 204options do not have long names. 205They take arguments and are described after the single letter options. 206.Bl -tag -width indent 207.It Fl a Li allexport 208Flag variables for export when assignments are made to them. 209.It Fl b Li notify 210Enable asynchronous notification of background job 211completion. 212(UNIMPLEMENTED) 213.It Fl C Li noclobber 214Do not overwrite existing files with 215.Ql > . 216.It Fl E Li emacs 217Enable the built-in 218.Xr emacs 1 219command line editor (disables the 220.Fl V 221option if it has been set; 222set automatically when interactive on terminals). 223.It Fl e Li errexit 224Exit immediately if any untested command fails in non-interactive mode. 225The exit status of a command is considered to be 226explicitly tested if the command is part of the list used to control 227an 228.Ic if , elif , while , 229or 230.Ic until ; 231if the command is the left 232hand operand of an 233.Dq Li && 234or 235.Dq Li || 236operator; or if the command is a pipeline preceded by the 237.Ic !\& 238keyword. 239If a shell function is executed and its exit status is explicitly 240tested, all commands of the function are considered to be tested as 241well. 242.Pp 243It is recommended to check for failures explicitly 244instead of relying on 245.Fl e 246because it tends to behave in unexpected ways, 247particularly in larger scripts. 248.It Fl f Li noglob 249Disable pathname expansion. 250.It Fl h Li trackall 251A do-nothing option for 252.Tn POSIX 253compliance. 254.It Fl I Li ignoreeof 255Ignore 256.Dv EOF Ap s 257from input when in interactive mode. 258.It Fl i Li interactive 259Force the shell to behave interactively. 260.It Fl m Li monitor 261Turn on job control (set automatically when interactive). 262A new process group is created for each pipeline (called a job). 263It is possible to suspend jobs or to have them run in the foreground or 264in the background. 265In a non-interactive shell, 266this option can be set even if no terminal is available 267and is useful to place processes in separate process groups. 268.It Fl n Li noexec 269If not interactive, read commands but do not 270execute them. 271This is useful for checking the 272syntax of shell scripts. 273.It Fl P Li physical 274Change the default for the 275.Ic cd 276and 277.Ic pwd 278commands from 279.Fl L 280(logical directory layout) 281to 282.Fl P 283(physical directory layout). 284.It Fl p Li privileged 285Turn on privileged mode. 286This mode is enabled on startup 287if either the effective user or group ID is not equal to the 288real user or group ID. 289Turning this mode off sets the 290effective user and group IDs to the real user and group IDs. 291When this mode is enabled for interactive shells, the file 292.Pa /etc/suid_profile 293is sourced instead of 294.Pa ~/.profile 295after 296.Pa /etc/profile 297is sourced, and the contents of the 298.Ev ENV 299variable are ignored. 300.It Fl s Li stdin 301Read commands from standard input (set automatically 302if no file arguments are present). 303This option has 304no effect when set after the shell has already started 305running (i.e., when set with the 306.Ic set 307command). 308.It Fl T Li trapsasync 309When waiting for a child, execute traps immediately. 310If this option is not set, 311traps are executed after the child exits, 312as specified in 313.St -p1003.2 . 314This nonstandard option is useful for putting guarding shells around 315children that block signals. 316The surrounding shell may kill the child 317or it may just return control to the tty and leave the child alone, 318like this: 319.Bd -literal -offset indent 320sh -T -c "trap 'exit 1' 2 ; some-blocking-program" 321.Ed 322.It Fl u Li nounset 323Write a message to standard error when attempting 324to expand a variable, a positional parameter or 325the special parameter 326.Va \&! 327that is not set, and if the 328shell is not interactive, exit immediately. 329.It Fl V Li vi 330Enable the built-in 331.Xr vi 1 332command line editor (disables 333.Fl E 334if it has been set). 335.It Fl v Li verbose 336The shell writes its input to standard error 337as it is read. 338Useful for debugging. 339.It Fl x Li xtrace 340Write each command 341(preceded by the value of the 342.Va PS4 343variable subjected to parameter expansion and arithmetic expansion) 344to standard error before it is executed. 345Useful for debugging. 346.El 347.Pp 348The 349.Fl c 350option causes the commands to be read from the 351.Ar string 352operand instead of from the standard input. 353Keep in mind that this option only accepts a single string as its 354argument, hence multi-word strings must be quoted. 355.Pp 356The 357.Fl /+o 358option takes as its only argument the long name of an option 359to be enabled or disabled. 360For example, the following two invocations of 361.Nm 362both enable the built-in 363.Xr emacs 1 364command line editor: 365.Bd -literal -offset indent 366set -E 367set -o emacs 368.Ed 369.Pp 370If used without an argument, the 371.Fl o 372option displays the current option settings in a human-readable format. 373If 374.Cm +o 375is used without an argument, the current option settings are output 376in a format suitable for re-input into the shell. 377.Ss Lexical Structure 378The shell reads input in terms of lines from a file and breaks 379it up into words at whitespace (blanks and tabs), and at 380certain sequences of 381characters called 382.Dq operators , 383which are special to the shell. 384There are two types of operators: control operators and 385redirection operators (their meaning is discussed later). 386The following is a list of valid operators: 387.Bl -tag -width indent 388.It Control operators: 389.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 390.It Li & Ta Li && Ta Li \&( Ta Li \&) Ta Li \en 391.It Li ;; Ta Li ;& Ta Li \&; Ta Li \&| Ta Li || 392.El 393.It Redirection operators: 394.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 395.It Li < Ta Li > Ta Li << Ta Li >> Ta Li <> 396.It Li <& Ta Li >& Ta Li <<- Ta Li >| Ta \& 397.El 398.El 399.Pp 400The character 401.Ql # 402introduces a comment if used at the beginning of a word. 403The word starting with 404.Ql # 405and the rest of the line are ignored. 406.Pp 407.Tn ASCII 408.Dv NUL 409characters (character code 0) are not allowed in shell input. 410.Ss Quoting 411Quoting is used to remove the special meaning of certain characters 412or words to the shell, such as operators, whitespace, keywords, 413or alias names. 414.Pp 415There are four types of quoting: matched single quotes, 416dollar-single quotes, 417matched double quotes, and backslash. 418.Bl -tag -width indent 419.It Single Quotes 420Enclosing characters in single quotes preserves the literal 421meaning of all the characters (except single quotes, making 422it impossible to put single-quotes in a single-quoted string). 423.It Dollar-Single Quotes 424Enclosing characters between 425.Li $' 426and 427.Li ' 428preserves the literal meaning of all characters 429except backslashes and single quotes. 430A backslash introduces a C-style escape sequence: 431.Bl -tag -width xUnnnnnnnn 432.It \ea 433Alert (ring the terminal bell) 434.It \eb 435Backspace 436.It \ec Ns Ar c 437The control character denoted by 438.Li ^ Ns Ar c 439in 440.Xr stty 1 . 441If 442.Ar c 443is a backslash, it must be doubled. 444.It \ee 445The ESC character 446.Tn ( ASCII 4470x1b) 448.It \ef 449Formfeed 450.It \en 451Newline 452.It \er 453Carriage return 454.It \et 455Horizontal tab 456.It \ev 457Vertical tab 458.It \e\e 459Literal backslash 460.It \e\&' 461Literal single-quote 462.It \e\&" 463Literal double-quote 464.It \e Ns Ar nnn 465The byte whose octal value is 466.Ar nnn 467(one to three digits) 468.It \ex Ns Ar nn 469The byte whose hexadecimal value is 470.Ar nn 471(one or more digits only the last two of which are used) 472.It \eu Ns Ar nnnn 473The Unicode code point 474.Ar nnnn 475(four hexadecimal digits) 476.It \eU Ns Ar nnnnnnnn 477The Unicode code point 478.Ar nnnnnnnn 479(eight hexadecimal digits) 480.El 481.Pp 482The sequences for Unicode code points are currently only useful with 483UTF-8 locales. 484They reject code point 0 and UTF-16 surrogates. 485.Pp 486If an escape sequence would produce a byte with value 0, 487that byte and the rest of the string until the matching single-quote 488are ignored. 489.Pp 490Any other string starting with a backslash is an error. 491.It Double Quotes 492Enclosing characters within double quotes preserves the literal 493meaning of all characters except dollar sign 494.Pq Ql $ , 495backquote 496.Pq Ql ` , 497and backslash 498.Pq Ql \e . 499The backslash inside double quotes is historically weird. 500It remains literal unless it precedes the following characters, 501which it serves to quote: 502.Pp 503.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 504.It Li $ Ta Li ` Ta Li \&" Ta Li \e Ta Li \en 505.El 506.It Backslash 507A backslash preserves the literal meaning of the following 508character, with the exception of the newline character 509.Pq Ql \en . 510A backslash preceding a newline is treated as a line continuation. 511.El 512.Ss Keywords 513Keywords or reserved words are words that have special meaning to the 514shell and are recognized at the beginning of a line and 515after a control operator. 516The following are keywords: 517.Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center 518.It Li \&! Ta { Ta } Ta Ic case Ta Ic do 519.It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi 520.It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while 521.El 522.Ss Aliases 523An alias is a name and corresponding value set using the 524.Ic alias 525built-in command. 526Wherever the command word of a simple command may occur, 527and after checking for keywords if a keyword may occur, the shell 528checks the word to see if it matches an alias. 529If it does, it replaces it in the input stream with its value. 530For example, if there is an alias called 531.Dq Li lf 532with the value 533.Dq Li "ls -F" , 534then the input 535.Pp 536.Dl "lf foobar" 537.Pp 538would become 539.Pp 540.Dl "ls -F foobar" 541.Pp 542Aliases are also recognized after an alias 543whose value ends with a space or tab. 544For example, if there is also an alias called 545.Dq Li nohup 546with the value 547.Dq Li "nohup " , 548then the input 549.Pp 550.Dl "nohup lf foobar" 551.Pp 552would become 553.Pp 554.Dl "nohup ls -F foobar" 555.Pp 556Aliases provide a convenient way for naive users to 557create shorthands for commands without having to learn how 558to create functions with arguments. 559Using aliases in scripts is discouraged 560because the command that defines them must be executed 561before the code that uses them is parsed. 562This is fragile and not portable. 563.Pp 564An alias name may be escaped in a command line, so that it is not 565replaced by its alias value, by using quoting characters within or 566adjacent to the alias name. 567This is most often done by prefixing 568an alias name with a backslash to execute a function, built-in, or 569normal program with the same name. 570See the 571.Sx Quoting 572subsection. 573.Ss Commands 574The shell interprets the words it reads according to a 575language, the specification of which is outside the scope 576of this man page (refer to the BNF in the 577.St -p1003.2 578document). 579Essentially though, a line is read and if 580the first word of the line (or after a control operator) 581is not a keyword, then the shell has recognized a 582simple command. 583Otherwise, a complex command or some 584other special construct may have been recognized. 585.Ss Simple Commands 586If a simple command has been recognized, the shell performs 587the following actions: 588.Bl -enum 589.It 590Leading words of the form 591.Dq Li name=value 592are stripped off and assigned to the environment of 593the simple command 594(they do not affect expansions). 595Redirection operators and 596their arguments (as described below) are stripped 597off and saved for processing. 598.It 599The remaining words are expanded as described in 600the section called 601.Sx Word Expansions , 602and the first remaining word is considered the command 603name and the command is located. 604The remaining 605words are considered the arguments of the command. 606If no command name resulted, then the 607.Dq Li name=value 608variable assignments recognized in 1) affect the 609current shell. 610.It 611Redirections are performed as described in 612the next section. 613.El 614.Ss Redirections 615Redirections are used to change where a command reads its input 616or sends its output. 617In general, redirections open, close, or 618duplicate an existing reference to a file. 619The overall format 620used for redirection is: 621.Pp 622.D1 Oo Ar n Oc Ar redir-op file 623.Pp 624The 625.Ar redir-op 626is one of the redirection operators mentioned 627previously. 628The following gives some examples of how these 629operators can be used. 630Note that stdin and stdout are commonly used abbreviations 631for standard input and standard output respectively. 632.Bl -tag -width "1234567890XX" -offset indent 633.It Oo Ar n Oc Ns Li > Ar file 634redirect stdout (or file descriptor 635.Ar n ) 636to 637.Ar file 638.It Oo Ar n Oc Ns Li >| Ar file 639same as above, but override the 640.Fl C 641option 642.It Oo Ar n Oc Ns Li >> Ar file 643append stdout (or file descriptor 644.Ar n ) 645to 646.Ar file 647.It Oo Ar n Oc Ns Li < Ar file 648redirect stdin (or file descriptor 649.Ar n ) 650from 651.Ar file 652.It Oo Ar n Oc Ns Li <> Ar file 653redirect stdin (or file descriptor 654.Ar n ) 655to and from 656.Ar file 657.It Oo Ar n1 Oc Ns Li <& Ns Ar n2 658duplicate stdin (or file descriptor 659.Ar n1 ) 660from file descriptor 661.Ar n2 662.It Oo Ar n Oc Ns Li <&- 663close stdin (or file descriptor 664.Ar n ) 665.It Oo Ar n1 Oc Ns Li >& Ns Ar n2 666duplicate stdout (or file descriptor 667.Ar n1 ) 668to file descriptor 669.Ar n2 670.It Oo Ar n Oc Ns Li >&- 671close stdout (or file descriptor 672.Ar n ) 673.El 674.Pp 675The following redirection is often called a 676.Dq here-document . 677.Bd -unfilled -offset indent 678.Oo Ar n Oc Ns Li << Ar delimiter 679.Ar here-doc-text 680.Ar ... 681.Ar delimiter 682.Ed 683.Pp 684All the text on successive lines up to the delimiter is 685saved away and made available to the command on standard 686input, or file descriptor 687.Ar n 688if it is specified. 689If the 690.Ar delimiter 691as specified on the initial line is quoted, then the 692.Ar here-doc-text 693is treated literally, otherwise the text is subjected to 694parameter expansion, command substitution, and arithmetic 695expansion (as described in the section on 696.Sx Word Expansions ) . 697If the operator is 698.Dq Li <<- 699instead of 700.Dq Li << , 701then leading tabs 702in the 703.Ar here-doc-text 704are stripped. 705.Ss Search and Execution 706There are three types of commands: shell functions, 707built-in commands, and normal programs. 708The command is searched for (by name) in that order. 709The three types of commands are all executed in a different way. 710.Pp 711When a shell function is executed, all of the shell positional 712parameters (except 713.Li $0 , 714which remains unchanged) are 715set to the arguments of the shell function. 716The variables which are explicitly placed in the environment of 717the command (by placing assignments to them before the 718function name) are made local to the function and are set 719to the values given. 720Then the command given in the function definition is executed. 721The positional parameters are restored to their original values 722when the command completes. 723This all occurs within the current shell. 724.Pp 725Shell built-in commands are executed internally to the shell, without 726spawning a new process. 727There are two kinds of built-in commands: regular and special. 728Assignments before special builtins persist after they finish 729executing and assignment errors, redirection errors and certain 730operand errors cause a script to be aborted. 731Special builtins cannot be overridden with a function. 732Both regular and special builtins can affect the shell in ways 733normal programs cannot. 734.Pp 735Otherwise, if the command name does not match a function 736or built-in command, the command is searched for as a normal 737program in the file system (as described in the next section). 738When a normal program is executed, the shell runs the program, 739passing the arguments and the environment to the program. 740If the program is not a normal executable file 741(i.e., if it does not begin with the 742.Dq "magic number" 743whose 744.Tn ASCII 745representation is 746.Dq Li #! , 747resulting in an 748.Er ENOEXEC 749return value from 750.Xr execve 2 ) 751but appears to be a text file, 752the shell will run a new instance of 753.Nm 754to interpret it. 755.Pp 756Note that previous versions of this document 757and the source code itself misleadingly and sporadically 758refer to a shell script without a magic number 759as a 760.Dq "shell procedure" . 761.Ss Path Search 762When locating a command, the shell first looks to see if 763it has a shell function by that name. 764Then it looks for a 765built-in command by that name. 766If a built-in command is not found, 767one of two things happen: 768.Bl -enum 769.It 770Command names containing a slash are simply executed without 771performing any searches. 772.It 773The shell searches each entry in the 774.Va PATH 775variable 776in turn for the command. 777The value of the 778.Va PATH 779variable should be a series of 780entries separated by colons. 781Each entry consists of a 782directory name. 783The current directory 784may be indicated implicitly by an empty directory name, 785or explicitly by a single period. 786.El 787.Ss Command Exit Status 788Each command has an exit status that can influence the behavior 789of other shell commands. 790The paradigm is that a command exits 791with zero for normal or success, and non-zero for failure, 792error, or a false indication. 793The man page for each command 794should indicate the various exit codes and what they mean. 795Additionally, the built-in commands return exit codes, as does 796an executed shell function. 797.Pp 798If a command is terminated by a signal, its exit status is greater than 128. 799The signal name can be found by passing the exit status to 800.Li kill -l . 801.Pp 802If there is no command word, 803the exit status is the exit status of the last command substitution executed, 804or zero if the command does not contain any command substitutions. 805.Ss Complex Commands 806Complex commands are combinations of simple commands 807with control operators or keywords, together creating a larger complex 808command. 809More generally, a command is one of the following: 810.Bl -item -offset indent 811.It 812simple command 813.It 814pipeline 815.It 816list or compound-list 817.It 818compound command 819.It 820function definition 821.El 822.Pp 823Unless otherwise stated, the exit status of a command is 824that of the last simple command executed by the command, 825or zero if no simple command was executed. 826.Ss Pipelines 827A pipeline is a sequence of one or more commands separated 828by the control operator 829.Ql \&| . 830The standard output of all but 831the last command is connected to the standard input 832of the next command. 833The standard output of the last 834command is inherited from the shell, as usual. 835.Pp 836The format for a pipeline is: 837.Pp 838.D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ... 839.Pp 840The standard output of 841.Ar command1 842is connected to the standard input of 843.Ar command2 . 844The standard input, standard output, or 845both of a command is considered to be assigned by the 846pipeline before any redirection specified by redirection 847operators that are part of the command. 848.Pp 849Note that unlike some other shells, 850.Nm 851executes each process in a pipeline with more than one command 852in a subshell environment and as a child of the 853.Nm 854process. 855.Pp 856If the pipeline is not in the background (discussed later), 857the shell waits for all commands to complete. 858.Pp 859If the keyword 860.Ic !\& 861does not precede the pipeline, the 862exit status is the exit status of the last command specified 863in the pipeline. 864Otherwise, the exit status is the logical 865NOT of the exit status of the last command. 866That is, if 867the last command returns zero, the exit status is 1; if 868the last command returns greater than zero, the exit status 869is zero. 870.Pp 871Because pipeline assignment of standard input or standard 872output or both takes place before redirection, it can be 873modified by redirection. 874For example: 875.Pp 876.Dl "command1 2>&1 | command2" 877.Pp 878sends both the standard output and standard error of 879.Ar command1 880to the standard input of 881.Ar command2 . 882.Pp 883A 884.Ql \&; 885or newline terminator causes the preceding 886AND-OR-list 887(described below in the section called 888.Sx Short-Circuit List Operators ) 889to be executed sequentially; 890an 891.Ql & 892causes asynchronous execution of the preceding AND-OR-list. 893.Ss Background Commands (&) 894If a command is terminated by the control operator ampersand 895.Pq Ql & , 896the shell executes the command in a subshell environment (see 897.Sx Grouping Commands Together 898below) and asynchronously; 899the shell does not wait for the command to finish 900before executing the next command. 901.Pp 902The format for running a command in background is: 903.Pp 904.D1 Ar command1 Li & Op Ar command2 Li & Ar ... 905.Pp 906If the shell is not interactive, the standard input of an 907asynchronous command is set to 908.Pa /dev/null . 909.Pp 910The exit status is zero. 911.Ss Lists (Generally Speaking) 912A list is a sequence of zero or more commands separated by 913newlines, semicolons, or ampersands, 914and optionally terminated by one of these three characters. 915The commands in a 916list are executed in the order they are written. 917If command is followed by an ampersand, the shell starts the 918command and immediately proceeds onto the next command; 919otherwise it waits for the command to terminate before 920proceeding to the next one. 921.Ss Short-Circuit List Operators 922.Dq Li && 923and 924.Dq Li || 925are AND-OR list operators. 926.Dq Li && 927executes the first command, and then executes the second command 928if the exit status of the first command is zero. 929.Dq Li || 930is similar, but executes the second command if the exit 931status of the first command is nonzero. 932.Dq Li && 933and 934.Dq Li || 935both have the same priority. 936.Ss Flow-Control Constructs (if, while, for, case) 937The syntax of the 938.Ic if 939command is: 940.Bd -unfilled -offset indent -compact 941.Ic if Ar list 942.Ic then Ar list 943.Oo Ic elif Ar list 944.Ic then Ar list Oc Ar ... 945.Op Ic else Ar list 946.Ic fi 947.Ed 948.Pp 949The exit status is that of selected 950.Ic then 951or 952.Ic else 953list, 954or zero if no list was selected. 955.Pp 956The syntax of the 957.Ic while 958command is: 959.Bd -unfilled -offset indent -compact 960.Ic while Ar list 961.Ic do Ar list 962.Ic done 963.Ed 964.Pp 965The two lists are executed repeatedly while the exit status of the 966first list is zero. 967The 968.Ic until 969command is similar, but has the word 970.Ic until 971in place of 972.Ic while , 973which causes it to 974repeat until the exit status of the first list is zero. 975.Pp 976The exit status is that of the last execution of the second list, 977or zero if it was never executed. 978.Pp 979The syntax of the 980.Ic for 981command is: 982.Bd -unfilled -offset indent -compact 983.Ic for Ar variable Op Ic in Ar word ... 984.Ic do Ar list 985.Ic done 986.Ed 987.Pp 988If 989.Ic in 990and the following words are omitted, 991.Ic in Li \&"$@\&" 992is used instead. 993The words are expanded, and then the list is executed 994repeatedly with the variable set to each word in turn. 995The 996.Ic do 997and 998.Ic done 999commands may be replaced with 1000.Ql { 1001and 1002.Ql } . 1003.Pp 1004The syntax of the 1005.Ic break 1006and 1007.Ic continue 1008commands is: 1009.D1 Ic break Op Ar num 1010.D1 Ic continue Op Ar num 1011.Pp 1012The 1013.Ic break 1014command terminates the 1015.Ar num 1016innermost 1017.Ic for 1018or 1019.Ic while 1020loops. 1021The 1022.Ic continue 1023command continues with the next iteration of the innermost loop. 1024These are implemented as special built-in commands. 1025.Pp 1026The syntax of the 1027.Ic case 1028command is: 1029.Bd -unfilled -offset indent -compact 1030.Ic case Ar word Ic in 1031.Ar pattern Ns Li ) Ar list Li ;; 1032.Ar ... 1033.Ic esac 1034.Ed 1035.Pp 1036The pattern can actually be one or more patterns 1037(see 1038.Sx Shell Patterns 1039described later), 1040separated by 1041.Ql \&| 1042characters. 1043Tilde expansion, parameter expansion, command substitution, 1044arithmetic expansion and quote removal are applied to the word. 1045Then, each pattern is expanded in turn using tilde expansion, 1046parameter expansion, command substitution and arithmetic expansion and 1047the expanded form of the word is checked against it. 1048If a match is found, the corresponding list is executed. 1049If the selected list is terminated by the control operator 1050.Ql ;& 1051instead of 1052.Ql ;; , 1053execution continues with the next list, 1054continuing until a list terminated with 1055.Ql ;; 1056or the end of the 1057.Ic case 1058command. 1059.Ss Grouping Commands Together 1060Commands may be grouped by writing either 1061.Pp 1062.D1 Li \&( Ns Ar list Ns Li \%) 1063.Pp 1064or 1065.Pp 1066.D1 Li { Ar list Ns Li \&; } 1067.Pp 1068The first form executes the commands in a subshell environment. 1069A subshell environment has its own copy of: 1070.Bl -enum 1071.It 1072The current working directory as set by 1073.Ic cd . 1074.It 1075The file creation mask as set by 1076.Ic umask . 1077.It 1078Resource limits as set by 1079.Ic ulimit . 1080.It 1081References to open files. 1082.It 1083Traps as set by 1084.Ic trap . 1085.It 1086Known jobs. 1087.It 1088Positional parameters and variables. 1089.It 1090Shell options. 1091.It 1092Shell functions. 1093.It 1094Shell aliases. 1095.El 1096.Pp 1097These are copied from the parent shell environment, 1098except that trapped (but not ignored) signals are reset to the default action 1099and known jobs are cleared. 1100Any changes do not affect the parent shell environment. 1101.Pp 1102A subshell environment may be implemented as a child process or differently. 1103If job control is enabled in an interactive shell, 1104commands grouped in parentheses can be suspended and continued as a unit. 1105.Pp 1106For compatibility with other shells, 1107two open parentheses in sequence should be separated by whitespace. 1108.Pp 1109The second form never forks another shell, 1110so it is slightly more efficient. 1111Grouping commands together this way allows the user to 1112redirect their output as though they were one program: 1113.Bd -literal -offset indent 1114{ echo -n "hello"; echo " world"; } > greeting 1115.Ed 1116.Ss Functions 1117The syntax of a function definition is 1118.Pp 1119.D1 Ar name Li \&( \&) Ar command 1120.Pp 1121A function definition is an executable statement; when 1122executed it installs a function named 1123.Ar name 1124and returns an 1125exit status of zero. 1126The 1127.Ar command 1128is normally a list 1129enclosed between 1130.Ql { 1131and 1132.Ql } . 1133.Pp 1134Variables may be declared to be local to a function by 1135using the 1136.Ic local 1137command. 1138This should appear as the first statement of a function, 1139and the syntax is: 1140.Pp 1141.D1 Ic local Oo Ar variable ... Oc Op Fl 1142.Pp 1143The 1144.Ic local 1145command is implemented as a built-in command. 1146The exit status is zero 1147unless the command is not in a function or a variable name is invalid. 1148.Pp 1149When a variable is made local, it inherits the initial 1150value and exported and readonly flags from the variable 1151with the same name in the surrounding scope, if there is 1152one. 1153Otherwise, the variable is initially unset. 1154The shell 1155uses dynamic scoping, so that if the variable 1156.Va x 1157is made local to function 1158.Em f , 1159which then calls function 1160.Em g , 1161references to the variable 1162.Va x 1163made inside 1164.Em g 1165will refer to the variable 1166.Va x 1167declared inside 1168.Em f , 1169not to the global variable named 1170.Va x . 1171.Pp 1172The only special parameter that can be made local is 1173.Ql - . 1174Making 1175.Ql - 1176local causes any shell options that are 1177changed via the 1178.Ic set 1179command inside the function to be 1180restored to their original values when the function 1181returns. 1182.Pp 1183The syntax of the 1184.Ic return 1185command is 1186.Pp 1187.D1 Ic return Op Ar exitstatus 1188.Pp 1189It terminates the current executional scope, returning from the closest 1190nested function or sourced script; 1191if no function or sourced script is being executed, 1192it exits the shell instance. 1193The 1194.Ic return 1195command is implemented as a special built-in command. 1196.Ss Variables and Parameters 1197The shell maintains a set of parameters. 1198A parameter 1199denoted by a name 1200(consisting solely 1201of alphabetics, numerics, and underscores, 1202and starting with an alphabetic or an underscore) 1203is called a variable. 1204When starting up, 1205the shell turns all environment variables with valid names into shell 1206variables. 1207New variables can be set using the form 1208.Pp 1209.D1 Ar name Ns = Ns Ar value 1210.Pp 1211A parameter can also be denoted by a number 1212or a special character as explained below. 1213.Pp 1214Assignments are expanded differently from other words: 1215tilde expansion is also performed after the equals sign and after any colon 1216and usernames are also terminated by colons, 1217and field splitting and pathname expansion are not performed. 1218.Pp 1219This special expansion applies not only to assignments that form a simple 1220command by themselves or precede a command word, 1221but also to words passed to the 1222.Ic export , 1223.Ic local 1224or 1225.Ic readonly 1226built-in commands that have this form. 1227For this, the builtin's name must be literal 1228(not the result of an expansion) 1229and may optionally be preceded by one or more literal instances of 1230.Ic command 1231without options. 1232.Ss Positional Parameters 1233A positional parameter is a parameter denoted by a number greater than zero. 1234The shell sets these initially to the values of its command line 1235arguments that follow the name of the shell script. 1236The 1237.Ic set 1238built-in command can also be used to set or reset them. 1239.Ss Special Parameters 1240Special parameters are parameters denoted by a single special character 1241or the digit zero. 1242They are shown in the following list, exactly as they would appear in input 1243typed by the user or in the source of a shell script. 1244.Bl -hang 1245.It Li $* 1246Expands to the positional parameters, starting from one. 1247When 1248the expansion occurs within a double-quoted string 1249it expands to a single field with the value of each parameter 1250separated by the first character of the 1251.Va IFS 1252variable, 1253or by a space if 1254.Va IFS 1255is unset. 1256.It Li $@ 1257Expands to the positional parameters, starting from one. 1258When 1259the expansion occurs within double-quotes, each positional 1260parameter expands as a separate argument. 1261If there are no positional parameters, the 1262expansion of 1263.Li @ 1264generates zero arguments, even when 1265.Li @ 1266is double-quoted. 1267What this basically means, for example, is 1268if 1269.Li $1 1270is 1271.Dq Li abc 1272and 1273.Li $2 1274is 1275.Dq Li "def ghi" , 1276then 1277.Li \&"$@\&" 1278expands to 1279the two arguments: 1280.Bd -literal -offset indent 1281"abc" "def ghi" 1282.Ed 1283.It Li $# 1284Expands to the number of positional parameters. 1285.It Li $? 1286Expands to the exit status of the most recent pipeline. 1287.It Li $- 1288(hyphen) Expands to the current option flags (the single-letter 1289option names concatenated into a string) as specified on 1290invocation, by the 1291.Ic set 1292built-in command, or implicitly 1293by the shell. 1294.It Li $$ 1295Expands to the process ID of the invoked shell. 1296A subshell 1297retains the same value of 1298.Va $ 1299as its parent. 1300.It Li $! 1301Expands to the process ID of the most recent background 1302command executed from the current shell. 1303For a 1304pipeline, the process ID is that of the last command in the 1305pipeline. 1306If this parameter is referenced, the shell will remember 1307the process ID and its exit status until the 1308.Ic wait 1309built-in command reports completion of the process. 1310.It Li $0 1311(zero) Expands to the name of the shell script if passed on the command line, 1312the 1313.Ar name 1314operand if given (with 1315.Fl c ) 1316or otherwise argument 0 passed to the shell. 1317.El 1318.Ss Special Variables 1319The following variables are set by the shell or 1320have special meaning to it: 1321.Bl -tag -width ".Va HISTSIZE" 1322.It Va CDPATH 1323The search path used with the 1324.Ic cd 1325built-in. 1326.It Va EDITOR 1327The fallback editor used with the 1328.Ic fc 1329built-in. 1330If not set, the default editor is 1331.Xr ed 1 . 1332.It Va FCEDIT 1333The default editor used with the 1334.Ic fc 1335built-in. 1336.It Va HISTSIZE 1337The number of previous commands that are accessible. 1338.It Va HOME 1339The user's home directory, 1340used in tilde expansion and as a default directory for the 1341.Ic cd 1342built-in. 1343.It Va IFS 1344Input Field Separators. 1345The default value is 1346.Aq space , 1347.Aq tab , 1348and 1349.Aq newline 1350in that order. 1351This default also applies if 1352.Va IFS 1353is unset, but not if it is set to the empty string. 1354See the 1355.Sx White Space Splitting 1356section for more details. 1357.It Va LINENO 1358The current line number in the script or function. 1359.It Va MAIL 1360The name of a mail file, that will be checked for the arrival of new 1361mail. 1362Overridden by 1363.Va MAILPATH . 1364.It Va MAILPATH 1365A colon 1366.Pq Ql \&: 1367separated list of file names, for the shell to check for incoming 1368mail. 1369This variable overrides the 1370.Va MAIL 1371setting. 1372There is a maximum of 10 mailboxes that can be monitored at once. 1373.It Va OPTIND 1374The index of the next argument to be processed by 1375.Ic getopts . 1376This is initialized to 1 at startup. 1377.It Va PATH 1378The default search path for executables. 1379See the 1380.Sx Path Search 1381section for details. 1382.It Va PPID 1383The parent process ID of the invoked shell. 1384This is set at startup 1385unless this variable is in the environment. 1386A later change of parent process ID is not reflected. 1387A subshell retains the same value of 1388.Va PPID . 1389.It Va PS1 1390The primary prompt string, which defaults to 1391.Dq Li "$ " , 1392unless you are the superuser, in which case it defaults to 1393.Dq Li "# " . 1394.Va PS1 1395may include any of the following formatting sequences, 1396which are replaced by the given information: 1397.Bl -tag -width indent 1398.It Li \eH 1399The local hostname. 1400.It Li \eh 1401The fully-qualified hostname. 1402.It Li \eW 1403The final component of the current working directory. 1404.It Li \ew 1405The entire path of the current working directory. 1406.It Li \e$ 1407Superuser status. 1408.Dq Li "$ " 1409for normal users and 1410.Dq Li "# " 1411for superusers. 1412.It Li \e\e 1413A literal backslash. 1414.El 1415.It Va PS2 1416The secondary prompt string, which defaults to 1417.Dq Li "> " . 1418.Va PS2 1419may include any of the formatting sequences from 1420.Va PS1 . 1421.It Va PS4 1422The prefix for the trace output (if 1423.Fl x 1424is active). 1425The default is 1426.Dq Li "+ " . 1427.El 1428.Ss Word Expansions 1429This clause describes the various expansions that are 1430performed on words. 1431Not all expansions are performed on 1432every word, as explained later. 1433.Pp 1434Tilde expansions, parameter expansions, command substitutions, 1435arithmetic expansions, and quote removals that occur within 1436a single word expand to a single field. 1437It is only field 1438splitting or pathname expansion that can create multiple 1439fields from a single word. 1440The single exception to this rule is 1441the expansion of the special parameter 1442.Va @ 1443within double-quotes, 1444as was described above. 1445.Pp 1446The order of word expansion is: 1447.Bl -enum 1448.It 1449Tilde Expansion, Parameter Expansion, Command Substitution, 1450Arithmetic Expansion (these all occur at the same time). 1451.It 1452Field Splitting is performed on fields generated by step (1) 1453unless the 1454.Va IFS 1455variable is null. 1456.It 1457Pathname Expansion (unless the 1458.Fl f 1459option is in effect). 1460.It 1461Quote Removal. 1462.El 1463.Pp 1464The 1465.Ql $ 1466character is used to introduce parameter expansion, command 1467substitution, or arithmetic expansion. 1468.Ss Tilde Expansion (substituting a user's home directory) 1469A word beginning with an unquoted tilde character 1470.Pq Ql ~ 1471is 1472subjected to tilde expansion. 1473All the characters up to a slash 1474.Pq Ql / 1475or the end of the word are treated as a username 1476and are replaced with the user's home directory. 1477If the 1478username is missing (as in 1479.Pa ~/foobar ) , 1480the tilde is replaced with the value of the 1481.Va HOME 1482variable (the current user's home directory). 1483.Ss Parameter Expansion 1484The format for parameter expansion is as follows: 1485.Pp 1486.D1 Li ${ Ns Ar expression Ns Li } 1487.Pp 1488where 1489.Ar expression 1490consists of all characters until the matching 1491.Ql } . 1492Any 1493.Ql } 1494escaped by a backslash or within a single-quoted or double-quoted 1495string, and characters in 1496embedded arithmetic expansions, command substitutions, and variable 1497expansions, are not examined in determining the matching 1498.Ql } . 1499If the variants with 1500.Ql + , 1501.Ql - , 1502.Ql = 1503or 1504.Ql ?\& 1505occur within a double-quoted string, 1506as an extension there may be unquoted parts 1507(via double-quotes inside the expansion); 1508.Ql } 1509within such parts are also not examined in determining the matching 1510.Ql } . 1511.Pp 1512The simplest form for parameter expansion is: 1513.Pp 1514.D1 Li ${ Ns Ar parameter Ns Li } 1515.Pp 1516The value, if any, of 1517.Ar parameter 1518is substituted. 1519.Pp 1520The parameter name or symbol can be enclosed in braces, which are 1521optional except for positional parameters with more than one digit or 1522when parameter is followed by a character that could be interpreted as 1523part of the name. 1524If a parameter expansion occurs inside double-quotes: 1525.Bl -enum 1526.It 1527Field splitting is not performed on the results of the 1528expansion, with the exception of the special parameter 1529.Va @ . 1530.It 1531Pathname expansion is not performed on the results of the 1532expansion. 1533.El 1534.Pp 1535In addition, a parameter expansion can be modified by using one of the 1536following formats. 1537.Bl -tag -width indent 1538.It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li } 1539Use Default Values. 1540If 1541.Ar parameter 1542is unset or null, the expansion of 1543.Ar word 1544is substituted; otherwise, the value of 1545.Ar parameter 1546is substituted. 1547.It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li } 1548Assign Default Values. 1549If 1550.Ar parameter 1551is unset or null, the expansion of 1552.Ar word 1553is assigned to 1554.Ar parameter . 1555In all cases, the 1556final value of 1557.Ar parameter 1558is substituted. 1559Quoting inside 1560.Ar word 1561does not prevent field splitting or pathname expansion. 1562Only variables, not positional 1563parameters or special parameters, can be 1564assigned in this way. 1565.It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li } 1566Indicate Error if Null or Unset. 1567If 1568.Ar parameter 1569is unset or null, the expansion of 1570.Ar word 1571(or a message indicating it is unset if 1572.Ar word 1573is omitted) is written to standard 1574error and the shell exits with a nonzero 1575exit status. 1576Otherwise, the value of 1577.Ar parameter 1578is substituted. 1579An 1580interactive shell need not exit. 1581.It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li } 1582Use Alternate Value. 1583If 1584.Ar parameter 1585is unset or null, null is substituted; 1586otherwise, the expansion of 1587.Ar word 1588is substituted. 1589.El 1590.Pp 1591In the parameter expansions shown previously, use of the colon in the 1592format results in a test for a parameter that is unset or null; omission 1593of the colon results in a test for a parameter that is only unset. 1594.Pp 1595The 1596.Ar word 1597inherits the type of quoting 1598(unquoted, double-quoted or here-document) 1599from the surroundings, 1600with the exception that a backslash that quotes a closing brace is removed 1601during quote removal. 1602.Bl -tag -width indent 1603.It Li ${# Ns Ar parameter Ns Li } 1604String Length. 1605The length in characters of 1606the value of 1607.Ar parameter . 1608.El 1609.Pp 1610The following four varieties of parameter expansion provide for substring 1611processing. 1612In each case, pattern matching notation 1613(see 1614.Sx Shell Patterns ) , 1615rather than regular expression notation, 1616is used to evaluate the patterns. 1617If parameter is one of the special parameters 1618.Va * 1619or 1620.Va @ , 1621the result of the expansion is unspecified. 1622Enclosing the full parameter expansion string in double-quotes does not 1623cause the following four varieties of pattern characters to be quoted, 1624whereas quoting characters within the braces has this effect. 1625.Bl -tag -width indent 1626.It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li } 1627Remove Smallest Suffix Pattern. 1628The 1629.Ar word 1630is expanded to produce a pattern. 1631The 1632parameter expansion then results in 1633.Ar parameter , 1634with the smallest portion of the 1635suffix matched by the pattern deleted. 1636.It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li } 1637Remove Largest Suffix Pattern. 1638The 1639.Ar word 1640is expanded to produce a pattern. 1641The 1642parameter expansion then results in 1643.Ar parameter , 1644with the largest portion of the 1645suffix matched by the pattern deleted. 1646.It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li } 1647Remove Smallest Prefix Pattern. 1648The 1649.Ar word 1650is expanded to produce a pattern. 1651The 1652parameter expansion then results in 1653.Ar parameter , 1654with the smallest portion of the 1655prefix matched by the pattern deleted. 1656.It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li } 1657Remove Largest Prefix Pattern. 1658The 1659.Ar word 1660is expanded to produce a pattern. 1661The 1662parameter expansion then results in 1663.Ar parameter , 1664with the largest portion of the 1665prefix matched by the pattern deleted. 1666.El 1667.Ss Command Substitution 1668Command substitution allows the output of a command to be substituted in 1669place of the command name itself. 1670Command substitution occurs when 1671the command is enclosed as follows: 1672.Pp 1673.D1 Li $( Ns Ar command Ns Li )\& 1674.Pp 1675or the backquoted version: 1676.Pp 1677.D1 Li ` Ns Ar command Ns Li ` 1678.Pp 1679The shell expands the command substitution by executing command 1680and replacing the command substitution 1681with the standard output of the command, 1682removing sequences of one or more newlines at the end of the substitution. 1683Embedded newlines before the end of the output are not removed; 1684however, during field splitting, they may be translated into spaces 1685depending on the value of 1686.Va IFS 1687and the quoting that is in effect. 1688The command is executed in a subshell environment, 1689except that the built-in commands 1690.Ic jobid , 1691.Ic jobs , 1692and 1693.Ic trap 1694return information about the parent shell environment 1695and 1696.Ic times 1697returns information about the same process 1698if they are the only command in a command substitution. 1699.Pp 1700If a command substitution of the 1701.Li $( 1702form begins with a subshell, 1703the 1704.Li $( 1705and 1706.Li (\& 1707must be separated by whitespace 1708to avoid ambiguity with arithmetic expansion. 1709.Ss Arithmetic Expansion 1710Arithmetic expansion provides a mechanism for evaluating an arithmetic 1711expression and substituting its value. 1712The format for arithmetic expansion is as follows: 1713.Pp 1714.D1 Li $(( Ns Ar expression Ns Li )) 1715.Pp 1716The 1717.Ar expression 1718is treated as if it were in double-quotes, except 1719that a double-quote inside the expression is not treated specially. 1720The 1721shell expands all tokens in the 1722.Ar expression 1723for parameter expansion, 1724command substitution, 1725arithmetic expansion 1726and quote removal. 1727.Pp 1728The allowed expressions are a subset of C expressions, 1729summarized below. 1730.Bl -tag -width "Variables" -offset indent 1731.It Values 1732All values are of type 1733.Ft intmax_t . 1734.It Constants 1735Decimal, octal (starting with 1736.Li 0 ) 1737and hexadecimal (starting with 1738.Li 0x ) 1739integer constants. 1740.It Variables 1741Shell variables can be read and written 1742and contain integer constants. 1743.It Unary operators 1744.Li "! ~ + -" 1745.It Binary operators 1746.Li "* / % + - << >> < <= > >= == != & ^ | && ||" 1747.It Assignment operators 1748.Li "= += -= *= /= %= <<= >>= &= ^= |=" 1749.It Conditional operator 1750.Li "? :" 1751.El 1752.Pp 1753The result of the expression is substituted in decimal. 1754.Ss White Space Splitting (Field Splitting) 1755In certain contexts, 1756after parameter expansion, command substitution, and 1757arithmetic expansion the shell scans the results of 1758expansions and substitutions that did not occur in double-quotes for 1759field splitting and multiple fields can result. 1760.Pp 1761Characters in 1762.Va IFS 1763that are whitespace 1764.Po 1765.Aq space , 1766.Aq tab , 1767and 1768.Aq newline 1769.Pc 1770are treated differently from other characters in 1771.Va IFS . 1772.Pp 1773Whitespace in 1774.Va IFS 1775at the beginning or end of a word is discarded. 1776.Pp 1777Subsequently, a field is delimited by either 1778.Bl -enum 1779.It 1780a non-whitespace character in 1781.Va IFS 1782with any whitespace in 1783.Va IFS 1784surrounding it, or 1785.It 1786one or more whitespace characters in 1787.Va IFS . 1788.El 1789.Pp 1790If a word ends with a non-whitespace character in 1791.Va IFS , 1792there is no empty field after this character. 1793.Pp 1794If no field is delimited, the word is discarded. 1795In particular, if a word consists solely of an unquoted substitution 1796and the result of the substitution is null, 1797it is removed by field splitting even if 1798.Va IFS 1799is null. 1800.Ss Pathname Expansion (File Name Generation) 1801Unless the 1802.Fl f 1803option is set, 1804file name generation is performed 1805after word splitting is complete. 1806Each word is 1807viewed as a series of patterns, separated by slashes. 1808The 1809process of expansion replaces the word with the names of 1810all existing files whose names can be formed by replacing 1811each pattern with a string that matches the specified pattern. 1812There are two restrictions on this: first, a pattern cannot match 1813a string containing a slash, and second, 1814a pattern cannot match a string starting with a period 1815unless the first character of the pattern is a period. 1816The next section describes the patterns used for 1817Pathname Expansion, 1818the four varieties of parameter expansion for substring processing and the 1819.Ic case 1820command. 1821.Ss Shell Patterns 1822A pattern consists of normal characters, which match themselves, 1823and meta-characters. 1824The meta-characters are 1825.Ql * , 1826.Ql \&? , 1827and 1828.Ql \&[ . 1829These characters lose their special meanings if they are quoted. 1830When command or variable substitution is performed and the dollar sign 1831or back quotes are not double-quoted, the value of the 1832variable or the output of the command is scanned for these 1833characters and they are turned into meta-characters. 1834.Pp 1835An asterisk 1836.Pq Ql * 1837matches any string of characters. 1838A question mark 1839.Pq Ql \&? 1840matches any single character. 1841A left bracket 1842.Pq Ql \&[ 1843introduces a character class. 1844The end of the character class is indicated by a 1845.Ql \&] ; 1846if the 1847.Ql \&] 1848is missing then the 1849.Ql \&[ 1850matches a 1851.Ql \&[ 1852rather than introducing a character class. 1853A character class matches any of the characters between the square brackets. 1854A locale-dependent range of characters may be specified using a minus sign. 1855A named class of characters (see 1856.Xr wctype 3 ) 1857may be specified by surrounding the name with 1858.Ql \&[: 1859and 1860.Ql :\&] . 1861For example, 1862.Ql \&[\&[:alpha:\&]\&] 1863is a shell pattern that matches a single letter. 1864The character class may be complemented by making an exclamation point 1865.Pq Ql !\& 1866the first character of the character class. 1867A caret 1868.Pq Ql ^ 1869has the same effect but is non-standard. 1870.Pp 1871To include a 1872.Ql \&] 1873in a character class, make it the first character listed 1874(after the 1875.Ql \&! 1876or 1877.Ql ^ , 1878if any). 1879To include a 1880.Ql - , 1881make it the first or last character listed. 1882.Ss Built-in Commands 1883This section lists the built-in commands. 1884.Bl -tag -width indent 1885.It Ic \&: 1886A null command that returns a 0 (true) exit value. 1887.It Ic \&. Ar file 1888The commands in the specified file are read and executed by the shell. 1889The 1890.Ic return 1891command may be used to return to the 1892.Ic \&. 1893command's caller. 1894If 1895.Ar file 1896contains any 1897.Ql / 1898characters, it is used as is. 1899Otherwise, the shell searches the 1900.Va PATH 1901for the file. 1902If it is not found in the 1903.Va PATH , 1904it is sought in the current working directory. 1905.It Ic \&[ 1906A built-in equivalent of 1907.Xr test 1 . 1908.It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc 1909If 1910.Ar name Ns = Ns Ar string 1911is specified, the shell defines the alias 1912.Ar name 1913with value 1914.Ar string . 1915If just 1916.Ar name 1917is specified, the value of the alias 1918.Ar name 1919is printed. 1920With no arguments, the 1921.Ic alias 1922built-in command prints the names and values of all defined aliases 1923(see 1924.Ic unalias ) . 1925Alias values are written with appropriate quoting so that they are 1926suitable for re-input to the shell. 1927Also see the 1928.Sx Aliases 1929subsection. 1930.It Ic bg Op Ar job ... 1931Continue the specified jobs 1932(or the current job if no jobs are given) 1933in the background. 1934.It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc 1935List or alter key bindings for the line editor. 1936This command is documented in 1937.Xr editrc 5 . 1938.It Ic break Op Ar num 1939See the 1940.Sx Flow-Control Constructs 1941subsection. 1942.It Ic builtin Ar cmd Op Ar arg ... 1943Execute the specified built-in command, 1944.Ar cmd . 1945This is useful when the user wishes to override a shell function 1946with the same name as a built-in command. 1947.It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory 1948Switch to the specified 1949.Ar directory , 1950or to the directory specified in the 1951.Va HOME 1952environment variable if no 1953.Ar directory 1954is specified. 1955If 1956.Ar directory 1957does not begin with 1958.Pa / , \&. , 1959or 1960.Pa .. , 1961then the directories listed in the 1962.Va CDPATH 1963variable will be 1964searched for the specified 1965.Ar directory . 1966If 1967.Va CDPATH 1968is unset, the current directory is searched. 1969The format of 1970.Va CDPATH 1971is the same as that of 1972.Va PATH . 1973In an interactive shell, 1974the 1975.Ic cd 1976command will print out the name of the directory 1977that it actually switched to 1978if this is different from the name that the user gave. 1979These may be different either because the 1980.Va CDPATH 1981mechanism was used or because a symbolic link was crossed. 1982.Pp 1983If the 1984.Fl P 1985option is specified, 1986.Pa .. 1987is handled physically and symbolic links are resolved before 1988.Pa .. 1989components are processed. 1990If the 1991.Fl L 1992option is specified, 1993.Pa .. 1994is handled logically. 1995This is the default. 1996.Pp 1997The 1998.Fl e 1999option causes 2000.Ic cd 2001to return exit status 1 if the full pathname of the new directory 2002cannot be determined reliably or at all. 2003Normally this is not considered an error, 2004although a warning is printed. 2005.It Ic chdir 2006A synonym for the 2007.Ic cd 2008built-in command. 2009.It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ... 2010.It Ic command Oo Fl p Oc Fl v Ar utility 2011.It Ic command Oo Fl p Oc Fl V Ar utility 2012The first form of invocation executes the specified 2013.Ar utility , 2014ignoring shell functions in the search. 2015If 2016.Ar utility 2017is a special builtin, 2018it is executed as if it were a regular builtin. 2019.Pp 2020If the 2021.Fl p 2022option is specified, the command search is performed using a 2023default value of 2024.Va PATH 2025that is guaranteed to find all of the standard utilities. 2026.Pp 2027If the 2028.Fl v 2029option is specified, 2030.Ar utility 2031is not executed but a description of its interpretation by the shell is 2032printed. 2033For ordinary commands the output is the path name; for shell built-in 2034commands, shell functions and keywords only the name is written. 2035Aliases are printed as 2036.Dq Ic alias Ar name Ns = Ns Ar value . 2037.Pp 2038The 2039.Fl V 2040option is identical to 2041.Fl v 2042except for the output. 2043It prints 2044.Dq Ar utility Ic is Ar description 2045where 2046.Ar description 2047is either 2048the path name to 2049.Ar utility , 2050a special shell builtin, 2051a shell builtin, 2052a shell function, 2053a shell keyword 2054or 2055an alias for 2056.Ar value . 2057.It Ic continue Op Ar num 2058See the 2059.Sx Flow-Control Constructs 2060subsection. 2061.It Ic echo Oo Fl e | n Oc Op Ar string ... 2062Print a space-separated list of the arguments to the standard output 2063and append a newline character. 2064.Bl -tag -width indent 2065.It Fl n 2066Suppress the output of the trailing newline. 2067.It Fl e 2068Process C-style backslash escape sequences. 2069The 2070.Ic echo 2071command understands the following character escapes: 2072.Bl -tag -width indent 2073.It \ea 2074Alert (ring the terminal bell) 2075.It \eb 2076Backspace 2077.It \ec 2078Suppress the trailing newline (this has the side-effect of truncating the 2079line if it is not the last character) 2080.It \ee 2081The ESC character 2082.Tn ( ASCII 20830x1b) 2084.It \ef 2085Formfeed 2086.It \en 2087Newline 2088.It \er 2089Carriage return 2090.It \et 2091Horizontal tab 2092.It \ev 2093Vertical tab 2094.It \e\e 2095Literal backslash 2096.It \e0nnn 2097(Zero) The character whose octal value is 2098.Ar nnn 2099.El 2100.Pp 2101If 2102.Ar string 2103is not enclosed in quotes then the backslash itself must be escaped 2104with a backslash to protect it from the shell. 2105For example 2106.Bd -literal -offset indent 2107$ echo -e "a\evb" 2108a 2109 b 2110$ echo -e a\e\evb 2111a 2112 b 2113$ echo -e "a\e\eb" 2114a\eb 2115$ echo -e a\e\e\e\eb 2116a\eb 2117.Ed 2118.El 2119.Pp 2120Only one of the 2121.Fl e 2122and 2123.Fl n 2124options may be specified. 2125.It Ic eval Ar string ... 2126Concatenate all the arguments with spaces. 2127Then re-parse and execute the command. 2128.It Ic exec Op Ar command Op arg ... 2129Unless 2130.Ar command 2131is omitted, 2132the shell process is replaced with the specified program 2133(which must be a real program, not a shell built-in command or function). 2134Any redirections on the 2135.Ic exec 2136command are marked as permanent, 2137so that they are not undone when the 2138.Ic exec 2139command finishes. 2140.It Ic exit Op Ar exitstatus 2141Terminate the shell process. 2142If 2143.Ar exitstatus 2144is given 2145it is used as the exit status of the shell. 2146Otherwise, if the shell is executing an 2147.Cm EXIT 2148trap, the exit status of the last command before the trap is used; 2149if the shell is executing a trap for a signal, 2150the shell exits by resending the signal to itself. 2151Otherwise, the exit status of the preceding command is used. 2152The exit status should be an integer between 0 and 255. 2153.It Ic export Ar name ... 2154.It Ic export Op Fl p 2155The specified names are exported so that they will 2156appear in the environment of subsequent commands. 2157The only way to un-export a variable is to 2158.Ic unset 2159it. 2160The shell allows the value of a variable to be set 2161at the same time as it is exported by writing 2162.Pp 2163.D1 Ic export Ar name Ns = Ns Ar value 2164.Pp 2165With no arguments the 2166.Ic export 2167command lists the names 2168of all exported variables. 2169If the 2170.Fl p 2171option is specified, the exported variables are printed as 2172.Dq Ic export Ar name Ns = Ns Ar value 2173lines, suitable for re-input to the shell. 2174.It Ic false 2175A null command that returns a non-zero (false) exit value. 2176.It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last 2177.It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last 2178.It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first 2179The 2180.Ic fc 2181built-in command lists, or edits and re-executes, 2182commands previously entered to an interactive shell. 2183.Bl -tag -width indent 2184.It Fl e Ar editor 2185Use the editor named by 2186.Ar editor 2187to edit the commands. 2188The 2189.Ar editor 2190string is a command name, 2191subject to search via the 2192.Va PATH 2193variable. 2194The value in the 2195.Va FCEDIT 2196variable is used as a default when 2197.Fl e 2198is not specified. 2199If 2200.Va FCEDIT 2201is null or unset, the value of the 2202.Va EDITOR 2203variable is used. 2204If 2205.Va EDITOR 2206is null or unset, 2207.Xr ed 1 2208is used as the editor. 2209.It Fl l No (ell) 2210List the commands rather than invoking 2211an editor on them. 2212The commands are written in the 2213sequence indicated by the 2214.Ar first 2215and 2216.Ar last 2217operands, as affected by 2218.Fl r , 2219with each command preceded by the command number. 2220.It Fl n 2221Suppress command numbers when listing with 2222.Fl l . 2223.It Fl r 2224Reverse the order of the commands listed 2225(with 2226.Fl l ) 2227or edited 2228(with neither 2229.Fl l 2230nor 2231.Fl s ) . 2232.It Fl s 2233Re-execute the command without invoking an editor. 2234.It Ar first 2235.It Ar last 2236Select the commands to list or edit. 2237The number of previous commands that can be accessed 2238are determined by the value of the 2239.Va HISTSIZE 2240variable. 2241The value of 2242.Ar first 2243or 2244.Ar last 2245or both are one of the following: 2246.Bl -tag -width indent 2247.It Oo Cm + Oc Ns Ar num 2248A positive number representing a command number; 2249command numbers can be displayed with the 2250.Fl l 2251option. 2252.It Fl Ar num 2253A negative decimal number representing the 2254command that was executed 2255.Ar num 2256of 2257commands previously. 2258For example, \-1 is the immediately previous command. 2259.It Ar string 2260A string indicating the most recently entered command 2261that begins with that string. 2262If the 2263.Ar old Ns = Ns Ar new 2264operand is not also specified with 2265.Fl s , 2266the string form of the first operand cannot contain an embedded equal sign. 2267.El 2268.El 2269.Pp 2270The following variables affect the execution of 2271.Ic fc : 2272.Bl -tag -width ".Va HISTSIZE" 2273.It Va FCEDIT 2274Name of the editor to use for history editing. 2275.It Va HISTSIZE 2276The number of previous commands that are accessible. 2277.El 2278.It Ic fg Op Ar job 2279Move the specified 2280.Ar job 2281or the current job to the foreground. 2282.It Ic getopts Ar optstring var 2283The 2284.Tn POSIX 2285.Ic getopts 2286command. 2287The 2288.Ic getopts 2289command deprecates the older 2290.Xr getopt 1 2291command. 2292The first argument should be a series of letters, each possibly 2293followed by a colon which indicates that the option takes an argument. 2294The specified variable is set to the parsed option. 2295The index of 2296the next argument is placed into the shell variable 2297.Va OPTIND . 2298If an option takes an argument, it is placed into the shell variable 2299.Va OPTARG . 2300If an invalid option is encountered, 2301.Ar var 2302is set to 2303.Ql \&? . 2304It returns a false value (1) when it encounters the end of the options. 2305A new set of arguments may be parsed by assigning 2306.Li OPTIND=1 . 2307.It Ic hash Oo Fl rv Oc Op Ar command ... 2308The shell maintains a hash table which remembers the locations of commands. 2309With no arguments whatsoever, the 2310.Ic hash 2311command prints out the contents of this table. 2312.Pp 2313With arguments, the 2314.Ic hash 2315command removes each specified 2316.Ar command 2317from the hash table (unless they are functions) and then locates it. 2318With the 2319.Fl v 2320option, 2321.Ic hash 2322prints the locations of the commands as it finds them. 2323The 2324.Fl r 2325option causes the 2326.Ic hash 2327command to delete all the entries in the hash table except for functions. 2328.It Ic jobid Op Ar job 2329Print the process IDs of the processes in the specified 2330.Ar job . 2331If the 2332.Ar job 2333argument is omitted, use the current job. 2334.It Ic jobs Oo Fl lps Oc Op Ar job ... 2335Print information about the specified jobs, or all jobs if no 2336.Ar job 2337argument is given. 2338The information printed includes job ID, status and command name. 2339.Pp 2340If the 2341.Fl l 2342option is specified, the PID of each job is also printed. 2343If the 2344.Fl p 2345option is specified, only the process IDs for the process group leaders 2346are printed, one per line. 2347If the 2348.Fl s 2349option is specified, only the PIDs of the job commands are printed, one per 2350line. 2351.It Ic kill 2352A built-in equivalent of 2353.Xr kill 1 2354that additionally supports sending signals to jobs. 2355.It Ic local Oo Ar variable ... Oc Op Fl 2356See the 2357.Sx Functions 2358subsection. 2359.It Ic printf 2360A built-in equivalent of 2361.Xr printf 1 . 2362.It Ic pwd Op Fl L | P 2363Print the path of the current directory. 2364The built-in command may 2365differ from the program of the same name because the 2366built-in command remembers what the current directory 2367is rather than recomputing it each time. 2368This makes 2369it faster. 2370However, if the current directory is 2371renamed, 2372the built-in version of 2373.Xr pwd 1 2374will continue to print the old name for the directory. 2375.Pp 2376If the 2377.Fl P 2378option is specified, symbolic links are resolved. 2379If the 2380.Fl L 2381option is specified, the shell's notion of the current directory 2382is printed (symbolic links are not resolved). 2383This is the default. 2384.It Ic read Oo Fl p Ar prompt Oc Oo 2385.Fl t Ar timeout Oc Oo Fl er Oc Ar variable ... 2386The 2387.Ar prompt 2388is printed if the 2389.Fl p 2390option is specified 2391and the standard input is a terminal. 2392Then a line is 2393read from the standard input. 2394The trailing newline 2395is deleted from the line and the line is split as 2396described in the section on 2397.Sx White Space Splitting (Field Splitting) 2398above, and 2399the pieces are assigned to the variables in order. 2400If there are more pieces than variables, the remaining 2401pieces (along with the characters in 2402.Va IFS 2403that separated them) 2404are assigned to the last variable. 2405If there are more variables than pieces, the remaining 2406variables are assigned the null string. 2407.Pp 2408Backslashes are treated specially, unless the 2409.Fl r 2410option is 2411specified. 2412If a backslash is followed by 2413a newline, the backslash and the newline will be 2414deleted. 2415If a backslash is followed by any other 2416character, the backslash will be deleted and the following 2417character will be treated as though it were not in 2418.Va IFS , 2419even if it is. 2420.Pp 2421If the 2422.Fl t 2423option is specified and the 2424.Ar timeout 2425elapses before a complete line of input is supplied, 2426the 2427.Ic read 2428command will return an exit status as if terminated by 2429.Dv SIGALRM 2430without assigning any values. 2431The 2432.Ar timeout 2433value may optionally be followed by one of 2434.Ql s , 2435.Ql m 2436or 2437.Ql h 2438to explicitly specify seconds, minutes or hours. 2439If none is supplied, 2440.Ql s 2441is assumed. 2442.Pp 2443The 2444.Fl e 2445option exists only for backward compatibility with older scripts. 2446.Pp 2447The exit status is 0 on success, 1 on end of file, 2448between 2 and 128 if an error occurs 2449and greater than 128 if a trapped signal interrupts 2450.Ic read . 2451.It Ic readonly Oo Fl p Oc Op Ar name ... 2452Each specified 2453.Ar name 2454is marked as read only, 2455so that it cannot be subsequently modified or unset. 2456The shell allows the value of a variable to be set 2457at the same time as it is marked read only 2458by using the following form: 2459.Pp 2460.D1 Ic readonly Ar name Ns = Ns Ar value 2461.Pp 2462With no arguments the 2463.Ic readonly 2464command lists the names of all read only variables. 2465If the 2466.Fl p 2467option is specified, the read-only variables are printed as 2468.Dq Ic readonly Ar name Ns = Ns Ar value 2469lines, suitable for re-input to the shell. 2470.It Ic return Op Ar exitstatus 2471See the 2472.Sx Functions 2473subsection. 2474.It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo 2475.Fl c Ar string Oc Op Fl - Ar arg ... 2476The 2477.Ic set 2478command performs three different functions: 2479.Bl -item 2480.It 2481With no arguments, it lists the values of all shell variables. 2482.It 2483If options are given, 2484either in short form or using the long 2485.Dq Fl /+o Ar longname 2486form, 2487it sets or clears the specified options as described in the section called 2488.Sx Argument List Processing . 2489.It 2490If the 2491.Dq Fl - 2492option is specified, 2493.Ic set 2494will replace the shell's positional parameters with the subsequent 2495arguments. 2496If no arguments follow the 2497.Dq Fl - 2498option, 2499all the positional parameters will be cleared, 2500which is equivalent to executing the command 2501.Dq Li "shift $#" . 2502The 2503.Dq Fl - 2504flag may be omitted when specifying arguments to be used 2505as positional replacement parameters. 2506This is not recommended, 2507because the first argument may begin with a dash 2508.Pq Ql - 2509or a plus 2510.Pq Ql + , 2511which the 2512.Ic set 2513command will interpret as a request to enable or disable options. 2514.El 2515.It Ic setvar Ar variable value 2516Assigns the specified 2517.Ar value 2518to the specified 2519.Ar variable . 2520The 2521.Ic setvar 2522command is intended to be used in functions that 2523assign values to variables whose names are passed as parameters. 2524In general it is better to write 2525.Dq Ar variable Ns = Ns Ar value 2526rather than using 2527.Ic setvar . 2528.It Ic shift Op Ar n 2529Shift the positional parameters 2530.Ar n 2531times, or once if 2532.Ar n 2533is not specified. 2534A shift sets the value of 2535.Li $1 2536to the value of 2537.Li $2 , 2538the value of 2539.Li $2 2540to the value of 2541.Li $3 , 2542and so on, 2543decreasing the value of 2544.Li $# 2545by one. 2546For portability, shifting if there are zero positional parameters 2547should be avoided, since the shell may abort. 2548.It Ic test 2549A built-in equivalent of 2550.Xr test 1 . 2551.It Ic times 2552Print the amount of time spent executing the shell process and its children. 2553The first output line shows the user and system times for the shell process 2554itself, the second one contains the user and system times for the 2555children. 2556.It Ic trap Oo Ar action Oc Ar signal ... 2557.It Ic trap Fl l 2558Cause the shell to parse and execute 2559.Ar action 2560when any specified 2561.Ar signal 2562is received. 2563The signals are specified by name or number. 2564In addition, the pseudo-signal 2565.Cm EXIT 2566may be used to specify an 2567.Ar action 2568that is performed when the shell terminates. 2569The 2570.Ar action 2571may be an empty string or a dash 2572.Pq Ql - ; 2573the former causes the specified signal to be ignored 2574and the latter causes the default action to be taken. 2575Omitting the 2576.Ar action 2577and using only signal numbers is another way to request the default action. 2578In a subshell or utility environment, 2579the shell resets trapped (but not ignored) signals to the default action. 2580The 2581.Ic trap 2582command has no effect on signals that were ignored on entry to the shell. 2583.Pp 2584Option 2585.Fl l 2586causes the 2587.Ic trap 2588command to display a list of valid signal names. 2589.It Ic true 2590A null command that returns a 0 (true) exit value. 2591.It Ic type Op Ar name ... 2592Interpret each 2593.Ar name 2594as a command and print the resolution of the command search. 2595Possible resolutions are: 2596shell keyword, alias, special shell builtin, shell builtin, command, 2597tracked alias 2598and not found. 2599For aliases the alias expansion is printed; 2600for commands and tracked aliases 2601the complete pathname of the command is printed. 2602.It Ic ulimit Oo Fl HSabcdfklmnpstuvw Oc Op Ar limit 2603Set or display resource limits (see 2604.Xr getrlimit 2 ) . 2605If 2606.Ar limit 2607is specified, the named resource will be set; 2608otherwise the current resource value will be displayed. 2609.Pp 2610If 2611.Fl H 2612is specified, the hard limits will be set or displayed. 2613While everybody is allowed to reduce a hard limit, 2614only the superuser can increase it. 2615The 2616.Fl S 2617option 2618specifies the soft limits instead. 2619When displaying limits, 2620only one of 2621.Fl S 2622or 2623.Fl H 2624can be given. 2625The default is to display the soft limits, 2626and to set both the hard and the soft limits. 2627.Pp 2628Option 2629.Fl a 2630causes the 2631.Ic ulimit 2632command to display all resources. 2633The parameter 2634.Ar limit 2635is not acceptable in this mode. 2636.Pp 2637The remaining options specify which resource value is to be 2638displayed or modified. 2639They are mutually exclusive. 2640.Bl -tag -width indent 2641.It Fl b Ar sbsize 2642The maximum size of socket buffer usage, in bytes. 2643.It Fl c Ar coredumpsize 2644The maximal size of core dump files, in 512-byte blocks. 2645.It Fl d Ar datasize 2646The maximal size of the data segment of a process, in kilobytes. 2647.It Fl f Ar filesize 2648The maximal size of a file, in 512-byte blocks. 2649.It Fl k Ar kqueues 2650The maximal number of kqueues 2651(see 2652.Xr kqueue 2 ) 2653for this user ID. 2654.It Fl l Ar lockedmem 2655The maximal size of memory that can be locked by a process, in 2656kilobytes. 2657.It Fl m Ar memoryuse 2658The maximal resident set size of a process, in kilobytes. 2659.It Fl n Ar nofiles 2660The maximal number of descriptors that could be opened by a process. 2661.It Fl p Ar pseudoterminals 2662The maximal number of pseudo-terminals for this user ID. 2663.It Fl s Ar stacksize 2664The maximal size of the stack segment, in kilobytes. 2665.It Fl t Ar time 2666The maximal amount of CPU time to be used by each process, in seconds. 2667.It Fl u Ar userproc 2668The maximal number of simultaneous processes for this user ID. 2669.It Fl v Ar virtualmem 2670The maximal virtual size of a process, in kilobytes. 2671.It Fl w Ar swapuse 2672The maximum amount of swap space reserved or used for this user ID, 2673in kilobytes. 2674.El 2675.It Ic umask Oo Fl S Oc Op Ar mask 2676Set the file creation mask (see 2677.Xr umask 2 ) 2678to the octal or symbolic (see 2679.Xr chmod 1 ) 2680value specified by 2681.Ar mask . 2682If the argument is omitted, the current mask value is printed. 2683If the 2684.Fl S 2685option is specified, the output is symbolic, otherwise the output is octal. 2686.It Ic unalias Oo Fl a Oc Op Ar name ... 2687The specified alias names are removed. 2688If 2689.Fl a 2690is specified, all aliases are removed. 2691.It Ic unset Oo Fl fv Oc Ar name ... 2692The specified variables or functions are unset and unexported. 2693If the 2694.Fl v 2695option is specified or no options are given, the 2696.Ar name 2697arguments are treated as variable names. 2698If the 2699.Fl f 2700option is specified, the 2701.Ar name 2702arguments are treated as function names. 2703.It Ic wait Op Ar job ... 2704Wait for each specified 2705.Ar job 2706to complete and return the exit status of the last process in the 2707last specified 2708.Ar job . 2709If any 2710.Ar job 2711specified is unknown to the shell, it is treated as if it 2712were a known job that exited with exit status 127. 2713If no operands are given, wait for all jobs to complete 2714and return an exit status of zero. 2715.El 2716.Ss Commandline Editing 2717When 2718.Nm 2719is being used interactively from a terminal, the current command 2720and the command history 2721(see 2722.Ic fc 2723in 2724.Sx Built-in Commands ) 2725can be edited using 2726.Nm vi Ns -mode 2727command line editing. 2728This mode uses commands similar 2729to a subset of those described in the 2730.Xr vi 1 2731man page. 2732The command 2733.Dq Li "set -o vi" 2734(or 2735.Dq Li "set -V" ) 2736enables 2737.Nm vi Ns -mode 2738editing and places 2739.Nm 2740into 2741.Nm vi 2742insert mode. 2743With 2744.Nm vi Ns -mode 2745enabled, 2746.Nm 2747can be switched between insert mode and command mode by typing 2748.Aq ESC . 2749Hitting 2750.Aq return 2751while in command mode will pass the line to the shell. 2752.Pp 2753Similarly, the 2754.Dq Li "set -o emacs" 2755(or 2756.Dq Li "set -E" ) 2757command can be used to enable a subset of 2758.Nm emacs Ns -style 2759command line editing features. 2760.Sh ENVIRONMENT 2761The following environment variables affect the execution of 2762.Nm : 2763.Bl -tag -width ".Ev LANGXXXXXX" 2764.It Ev ENV 2765Initialization file for interactive shells. 2766.It Ev LANG , Ev LC_* 2767Locale settings. 2768These are inherited by children of the shell, 2769and is used in a limited manner by the shell itself. 2770.It Ev PWD 2771An absolute pathname for the current directory, 2772possibly containing symbolic links. 2773This is used and updated by the shell. 2774.It Ev TERM 2775The default terminal setting for the shell. 2776This is inherited by children of the shell, and is used in the history 2777editing modes. 2778.El 2779.Pp 2780Additionally, environment variables are turned into shell variables 2781at startup, 2782which may affect the shell as described under 2783.Sx Special Variables . 2784.Sh FILES 2785.Bl -tag -width "/etc/suid_profileXX" -compact 2786.It Pa ~/.profile 2787User's login profile. 2788.It Pa /etc/profile 2789System login profile. 2790.It Pa /etc/shells 2791Shell database. 2792.It Pa /etc/suid_profile 2793Privileged shell profile. 2794.El 2795.Sh EXIT STATUS 2796Errors that are detected by the shell, such as a syntax error, will 2797cause the shell to exit with a non-zero exit status. 2798If the shell is not an interactive shell, the execution of the shell 2799file will be aborted. 2800Otherwise the shell will return the exit status of the last command 2801executed, or if the 2802.Ic exit 2803builtin is used with a numeric argument, it 2804will return the argument. 2805.Sh SEE ALSO 2806.Xr builtin 1 , 2807.Xr chsh 1 , 2808.Xr echo 1 , 2809.Xr ed 1 , 2810.Xr emacs 1 Pq Pa editors/emacs , 2811.Xr kill 1 , 2812.Xr printf 1 , 2813.Xr pwd 1 , 2814.Xr test 1 , 2815.Xr vi 1 , 2816.Xr execve 2 , 2817.Xr getrlimit 2 , 2818.Xr umask 2 , 2819.Xr wctype 3 , 2820.Xr editrc 5 , 2821.Xr shells 5 2822.Sh HISTORY 2823A 2824.Nm 2825command, the Thompson shell, appeared in 2826.At v1 . 2827It was superseded in 2828.At v7 2829by the Bourne shell, which inherited the name 2830.Nm . 2831.Pp 2832This version of 2833.Nm 2834was rewritten in 1989 under the 2835.Bx 2836license after the Bourne shell from 2837.At V.4 . 2838.Sh AUTHORS 2839This version of 2840.Nm 2841was originally written by 2842.An Kenneth Almquist . 2843.Sh BUGS 2844The 2845.Nm 2846utility does not recognize multibyte characters other than UTF-8. 2847Splitting using 2848.Va IFS 2849and the line editing library 2850.Xr editline 3 2851do not recognize multibyte characters. 2852