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: head/bin/sh/sh.1 251763 2013-06-14 22:06:18Z jilles $ 34.\" 35.Dd June 14, 2013 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 /+abCEefIimnPpTuVvx 44.Op Fl /+o Ar longname 45.Oo 46.Ar script 47.Op Ar arg ... 48.Oc 49.Nm 50.Op Fl /+abCEefIimnPpTuVvx 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 /+abCEefIimnPpTuVvx 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 !\& 238operator. 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.It Fl f Li noglob 243Disable pathname expansion. 244.It Fl h Li trackall 245A do-nothing option for 246.Tn POSIX 247compliance. 248.It Fl I Li ignoreeof 249Ignore 250.Dv EOF Ap s 251from input when in interactive mode. 252.It Fl i Li interactive 253Force the shell to behave interactively. 254.It Fl m Li monitor 255Turn on job control (set automatically when interactive). 256.It Fl n Li noexec 257If not interactive, read commands but do not 258execute them. 259This is useful for checking the 260syntax of shell scripts. 261.It Fl P Li physical 262Change the default for the 263.Ic cd 264and 265.Ic pwd 266commands from 267.Fl L 268(logical directory layout) 269to 270.Fl P 271(physical directory layout). 272.It Fl p Li privileged 273Turn on privileged mode. 274This mode is enabled on startup 275if either the effective user or group ID is not equal to the 276real user or group ID. 277Turning this mode off sets the 278effective user and group IDs to the real user and group IDs. 279When this mode is enabled for interactive shells, the file 280.Pa /etc/suid_profile 281is sourced instead of 282.Pa ~/.profile 283after 284.Pa /etc/profile 285is sourced, and the contents of the 286.Ev ENV 287variable are ignored. 288.It Fl s Li stdin 289Read commands from standard input (set automatically 290if no file arguments are present). 291This option has 292no effect when set after the shell has already started 293running (i.e., when set with the 294.Ic set 295command). 296.It Fl T Li trapsasync 297When waiting for a child, execute traps immediately. 298If this option is not set, 299traps are executed after the child exits, 300as specified in 301.St -p1003.2 . 302This nonstandard option is useful for putting guarding shells around 303children that block signals. 304The surrounding shell may kill the child 305or it may just return control to the tty and leave the child alone, 306like this: 307.Bd -literal -offset indent 308sh -T -c "trap 'exit 1' 2 ; some-blocking-program" 309.Ed 310.It Fl u Li nounset 311Write a message to standard error when attempting 312to expand a variable, a positional parameter or 313the special parameter 314.Va \&! 315that is not set, and if the 316shell is not interactive, exit immediately. 317.It Fl V Li vi 318Enable the built-in 319.Xr vi 1 320command line editor (disables 321.Fl E 322if it has been set). 323.It Fl v Li verbose 324The shell writes its input to standard error 325as it is read. 326Useful for debugging. 327.It Fl x Li xtrace 328Write each command 329(preceded by the value of the 330.Va PS4 331variable subjected to parameter expansion and arithmetic expansion) 332to standard error before it is executed. 333Useful for debugging. 334.It "\ \ " Em tabcomplete 335Enables filename completion in the command line editor. 336Typing a tab character will extend the current input word to match a 337filename. 338If more than one filename matches it is only extended to be the common prefix. 339Typing a second tab character will list all the matching names. 340Turned on by default in an interactive shell. 341.El 342.Pp 343The 344.Fl c 345option causes the commands to be read from the 346.Ar string 347operand instead of from the standard input. 348Keep in mind that this option only accepts a single string as its 349argument, hence multi-word strings must be quoted. 350.Pp 351The 352.Fl /+o 353option takes as its only argument the long name of an option 354to be enabled or disabled. 355For example, the following two invocations of 356.Nm 357both enable the built-in 358.Xr emacs 1 359command line editor: 360.Bd -literal -offset indent 361set -E 362set -o emacs 363.Ed 364.Pp 365If used without an argument, the 366.Fl o 367option displays the current option settings in a human-readable format. 368If 369.Cm +o 370is used without an argument, the current option settings are output 371in a format suitable for re-input into the shell. 372.Ss Lexical Structure 373The shell reads input in terms of lines from a file and breaks 374it up into words at whitespace (blanks and tabs), and at 375certain sequences of 376characters called 377.Dq operators , 378which are special to the shell. 379There are two types of operators: control operators and 380redirection operators (their meaning is discussed later). 381The following is a list of valid operators: 382.Bl -tag -width indent 383.It Control operators: 384.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 385.It Li & Ta Li && Ta Li \&( Ta Li \&) Ta Li \en 386.It Li ;; Ta Li ;& Ta Li \&; Ta Li \&| Ta Li || 387.El 388.It Redirection operators: 389.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 390.It Li < Ta Li > Ta Li << Ta Li >> Ta Li <> 391.It Li <& Ta Li >& Ta Li <<- Ta Li >| Ta \& 392.El 393.El 394.Pp 395The character 396.Ql # 397introduces a comment if used at the beginning of a word. 398The word starting with 399.Ql # 400and the rest of the line are ignored. 401.Pp 402.Tn ASCII 403.Dv NUL 404characters (character code 0) are not allowed in shell input. 405.Ss Quoting 406Quoting is used to remove the special meaning of certain characters 407or words to the shell, such as operators, whitespace, keywords, 408or alias names. 409.Pp 410There are four types of quoting: matched single quotes, 411dollar-single quotes, 412matched double quotes, and backslash. 413.Bl -tag -width indent 414.It Single Quotes 415Enclosing characters in single quotes preserves the literal 416meaning of all the characters (except single quotes, making 417it impossible to put single-quotes in a single-quoted string). 418.It Dollar-Single Quotes 419Enclosing characters between 420.Li $' 421and 422.Li ' 423preserves the literal meaning of all characters 424except backslashes and single quotes. 425A backslash introduces a C-style escape sequence: 426.Bl -tag -width xUnnnnnnnn 427.It \ea 428Alert (ring the terminal bell) 429.It \eb 430Backspace 431.It \ec Ns Ar c 432The control character denoted by 433.Li ^ Ns Ar c 434in 435.Xr stty 1 . 436If 437.Ar c 438is a backslash, it must be doubled. 439.It \ee 440The ESC character 441.Tn ( ASCII 4420x1b) 443.It \ef 444Formfeed 445.It \en 446Newline 447.It \er 448Carriage return 449.It \et 450Horizontal tab 451.It \ev 452Vertical tab 453.It \e\e 454Literal backslash 455.It \e\&' 456Literal single-quote 457.It \e\&" 458Literal double-quote 459.It \e Ns Ar nnn 460The byte whose octal value is 461.Ar nnn 462(one to three digits) 463.It \ex Ns Ar nn 464The byte whose hexadecimal value is 465.Ar nn 466(one or more digits only the last two of which are used) 467.It \eu Ns Ar nnnn 468The Unicode code point 469.Ar nnnn 470(four hexadecimal digits) 471.It \eU Ns Ar nnnnnnnn 472The Unicode code point 473.Ar nnnnnnnn 474(eight hexadecimal digits) 475.El 476.Pp 477The sequences for Unicode code points are currently only useful with 478UTF-8 locales. 479They reject code point 0 and UTF-16 surrogates. 480.Pp 481If an escape sequence would produce a byte with value 0, 482that byte and the rest of the string until the matching single-quote 483are ignored. 484.Pp 485Any other string starting with a backslash is an error. 486.It Double Quotes 487Enclosing characters within double quotes preserves the literal 488meaning of all characters except dollar sign 489.Pq Ql $ , 490backquote 491.Pq Ql ` , 492and backslash 493.Pq Ql \e . 494The backslash inside double quotes is historically weird. 495It remains literal unless it precedes the following characters, 496which it serves to quote: 497.Pp 498.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 499.It Li $ Ta Li ` Ta Li \&" Ta Li \e Ta Li \en 500.El 501.It Backslash 502A backslash preserves the literal meaning of the following 503character, with the exception of the newline character 504.Pq Ql \en . 505A backslash preceding a newline is treated as a line continuation. 506.El 507.Ss Keywords 508Keywords or reserved words are words that have special meaning to the 509shell and are recognized at the beginning of a line and 510after a control operator. 511The following are keywords: 512.Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center 513.It Li \&! Ta { Ta } Ta Ic case Ta Ic do 514.It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi 515.It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while 516.El 517.Ss Aliases 518An alias is a name and corresponding value set using the 519.Ic alias 520built-in command. 521Wherever the command word of a simple command may occur, 522and after checking for keywords if a keyword may occur, the shell 523checks the word to see if it matches an alias. 524If it does, it replaces it in the input stream with its value. 525For example, if there is an alias called 526.Dq Li lf 527with the value 528.Dq Li "ls -F" , 529then the input 530.Pp 531.Dl "lf foobar" 532.Pp 533would become 534.Pp 535.Dl "ls -F foobar" 536.Pp 537Aliases provide a convenient way for naive users to 538create shorthands for commands without having to learn how 539to create functions with arguments. 540Using aliases in scripts is discouraged 541because the command that defines them must be executed 542before the code that uses them is parsed. 543This is fragile and not portable. 544.Pp 545An alias name may be escaped in a command line, so that it is not 546replaced by its alias value, by using quoting characters within or 547adjacent to the alias name. 548This is most often done by prefixing 549an alias name with a backslash to execute a function, built-in, or 550normal program with the same name. 551See the 552.Sx Quoting 553subsection. 554.Ss Commands 555The shell interprets the words it reads according to a 556language, the specification of which is outside the scope 557of this man page (refer to the BNF in the 558.St -p1003.2 559document). 560Essentially though, a line is read and if 561the first word of the line (or after a control operator) 562is not a keyword, then the shell has recognized a 563simple command. 564Otherwise, a complex command or some 565other special construct may have been recognized. 566.Ss Simple Commands 567If a simple command has been recognized, the shell performs 568the following actions: 569.Bl -enum 570.It 571Leading words of the form 572.Dq Li name=value 573are stripped off and assigned to the environment of 574the simple command. 575Redirection operators and 576their arguments (as described below) are stripped 577off and saved for processing. 578.It 579The remaining words are expanded as described in 580the section called 581.Sx Word Expansions , 582and the first remaining word is considered the command 583name and the command is located. 584The remaining 585words are considered the arguments of the command. 586If no command name resulted, then the 587.Dq Li name=value 588variable assignments recognized in 1) affect the 589current shell. 590.It 591Redirections are performed as described in 592the next section. 593.El 594.Ss Redirections 595Redirections are used to change where a command reads its input 596or sends its output. 597In general, redirections open, close, or 598duplicate an existing reference to a file. 599The overall format 600used for redirection is: 601.Pp 602.D1 Oo Ar n Oc Ar redir-op file 603.Pp 604The 605.Ar redir-op 606is one of the redirection operators mentioned 607previously. 608The following gives some examples of how these 609operators can be used. 610Note that stdin and stdout are commonly used abbreviations 611for standard input and standard output respectively. 612.Bl -tag -width "1234567890XX" -offset indent 613.It Oo Ar n Oc Ns Li > Ar file 614redirect stdout (or file descriptor 615.Ar n ) 616to 617.Ar file 618.It Oo Ar n Oc Ns Li >| Ar file 619same as above, but override the 620.Fl C 621option 622.It Oo Ar n Oc Ns Li >> Ar file 623append stdout (or file descriptor 624.Ar n ) 625to 626.Ar file 627.It Oo Ar n Oc Ns Li < Ar file 628redirect stdin (or file descriptor 629.Ar n ) 630from 631.Ar file 632.It Oo Ar n Oc Ns Li <> Ar file 633redirect stdin (or file descriptor 634.Ar n ) 635to and from 636.Ar file 637.It Oo Ar n1 Oc Ns Li <& Ns Ar n2 638duplicate stdin (or file descriptor 639.Ar n1 ) 640from file descriptor 641.Ar n2 642.It Oo Ar n Oc Ns Li <&- 643close stdin (or file descriptor 644.Ar n ) 645.It Oo Ar n1 Oc Ns Li >& Ns Ar n2 646duplicate stdout (or file descriptor 647.Ar n1 ) 648to file descriptor 649.Ar n2 650.It Oo Ar n Oc Ns Li >&- 651close stdout (or file descriptor 652.Ar n ) 653.El 654.Pp 655The following redirection is often called a 656.Dq here-document . 657.Bd -unfilled -offset indent 658.Oo Ar n Oc Ns Li << Ar delimiter 659.Ar here-doc-text 660.Ar ... 661.Ar delimiter 662.Ed 663.Pp 664All the text on successive lines up to the delimiter is 665saved away and made available to the command on standard 666input, or file descriptor 667.Ar n 668if it is specified. 669If the 670.Ar delimiter 671as specified on the initial line is quoted, then the 672.Ar here-doc-text 673is treated literally, otherwise the text is subjected to 674parameter expansion, command substitution, and arithmetic 675expansion (as described in the section on 676.Sx Word Expansions ) . 677If the operator is 678.Dq Li <<- 679instead of 680.Dq Li << , 681then leading tabs 682in the 683.Ar here-doc-text 684are stripped. 685.Ss Search and Execution 686There are three types of commands: shell functions, 687built-in commands, and normal programs. 688The command is searched for (by name) in that order. 689The three types of commands are all executed in a different way. 690.Pp 691When a shell function is executed, all of the shell positional 692parameters (except 693.Li $0 , 694which remains unchanged) are 695set to the arguments of the shell function. 696The variables which are explicitly placed in the environment of 697the command (by placing assignments to them before the 698function name) are made local to the function and are set 699to the values given. 700Then the command given in the function definition is executed. 701The positional parameters are restored to their original values 702when the command completes. 703This all occurs within the current shell. 704.Pp 705Shell built-in commands are executed internally to the shell, without 706spawning a new process. 707There are two kinds of built-in commands: regular and special. 708Assignments before special builtins persist after they finish 709executing and assignment errors, redirection errors and certain 710operand errors cause a script to be aborted. 711Special builtins cannot be overridden with a function. 712Both regular and special builtins can affect the shell in ways 713normal programs cannot. 714.Pp 715Otherwise, if the command name does not match a function 716or built-in command, the command is searched for as a normal 717program in the file system (as described in the next section). 718When a normal program is executed, the shell runs the program, 719passing the arguments and the environment to the program. 720If the program is not a normal executable file 721(i.e., if it does not begin with the 722.Dq "magic number" 723whose 724.Tn ASCII 725representation is 726.Dq Li #! , 727resulting in an 728.Er ENOEXEC 729return value from 730.Xr execve 2 ) 731but appears to be a text file, 732the shell will run a new instance of 733.Nm 734to interpret it. 735.Pp 736Note that previous versions of this document 737and the source code itself misleadingly and sporadically 738refer to a shell script without a magic number 739as a 740.Dq "shell procedure" . 741.Ss Path Search 742When locating a command, the shell first looks to see if 743it has a shell function by that name. 744Then it looks for a 745built-in command by that name. 746If a built-in command is not found, 747one of two things happen: 748.Bl -enum 749.It 750Command names containing a slash are simply executed without 751performing any searches. 752.It 753The shell searches each entry in the 754.Va PATH 755variable 756in turn for the command. 757The value of the 758.Va PATH 759variable should be a series of 760entries separated by colons. 761Each entry consists of a 762directory name. 763The current directory 764may be indicated implicitly by an empty directory name, 765or explicitly by a single period. 766.El 767.Ss Command Exit Status 768Each command has an exit status that can influence the behavior 769of other shell commands. 770The paradigm is that a command exits 771with zero for normal or success, and non-zero for failure, 772error, or a false indication. 773The man page for each command 774should indicate the various exit codes and what they mean. 775Additionally, the built-in commands return exit codes, as does 776an executed shell function. 777.Pp 778If a command is terminated by a signal, its exit status is 128 plus 779the signal number. 780Signal numbers are defined in the header file 781.In sys/signal.h . 782.Ss Complex Commands 783Complex commands are combinations of simple commands 784with control operators or keywords, together creating a larger complex 785command. 786More generally, a command is one of the following: 787.Bl -item -offset indent 788.It 789simple command 790.It 791pipeline 792.It 793list or compound-list 794.It 795compound command 796.It 797function definition 798.El 799.Pp 800Unless otherwise stated, the exit status of a command is 801that of the last simple command executed by the command. 802.Ss Pipelines 803A pipeline is a sequence of one or more commands separated 804by the control operator 805.Ql \&| . 806The standard output of all but 807the last command is connected to the standard input 808of the next command. 809The standard output of the last 810command is inherited from the shell, as usual. 811.Pp 812The format for a pipeline is: 813.Pp 814.D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ... 815.Pp 816The standard output of 817.Ar command1 818is connected to the standard input of 819.Ar command2 . 820The standard input, standard output, or 821both of a command is considered to be assigned by the 822pipeline before any redirection specified by redirection 823operators that are part of the command. 824.Pp 825Note that unlike some other shells, 826.Nm 827executes each process in a pipeline with more than one command 828in a subshell environment and as a child of the 829.Nm 830process. 831.Pp 832If the pipeline is not in the background (discussed later), 833the shell waits for all commands to complete. 834.Pp 835If the keyword 836.Ic !\& 837does not precede the pipeline, the 838exit status is the exit status of the last command specified 839in the pipeline. 840Otherwise, the exit status is the logical 841NOT of the exit status of the last command. 842That is, if 843the last command returns zero, the exit status is 1; if 844the last command returns greater than zero, the exit status 845is zero. 846.Pp 847Because pipeline assignment of standard input or standard 848output or both takes place before redirection, it can be 849modified by redirection. 850For example: 851.Pp 852.Dl "command1 2>&1 | command2" 853.Pp 854sends both the standard output and standard error of 855.Ar command1 856to the standard input of 857.Ar command2 . 858.Pp 859A 860.Ql \&; 861or newline terminator causes the preceding 862AND-OR-list 863(described below in the section called 864.Sx Short-Circuit List Operators ) 865to be executed sequentially; 866an 867.Ql & 868causes asynchronous execution of the preceding AND-OR-list. 869.Ss Background Commands (&) 870If a command is terminated by the control operator ampersand 871.Pq Ql & , 872the shell executes the command in a subshell environment (see 873.Sx Grouping Commands Together 874below) and asynchronously; 875the shell does not wait for the command to finish 876before executing the next command. 877.Pp 878The format for running a command in background is: 879.Pp 880.D1 Ar command1 Li & Op Ar command2 Li & Ar ... 881.Pp 882If the shell is not interactive, the standard input of an 883asynchronous command is set to 884.Pa /dev/null . 885.Ss Lists (Generally Speaking) 886A list is a sequence of zero or more commands separated by 887newlines, semicolons, or ampersands, 888and optionally terminated by one of these three characters. 889The commands in a 890list are executed in the order they are written. 891If command is followed by an ampersand, the shell starts the 892command and immediately proceeds onto the next command; 893otherwise it waits for the command to terminate before 894proceeding to the next one. 895.Ss Short-Circuit List Operators 896.Dq Li && 897and 898.Dq Li || 899are AND-OR list operators. 900.Dq Li && 901executes the first command, and then executes the second command 902if the exit status of the first command is zero. 903.Dq Li || 904is similar, but executes the second command if the exit 905status of the first command is nonzero. 906.Dq Li && 907and 908.Dq Li || 909both have the same priority. 910.Ss Flow-Control Constructs (if, while, for, case) 911The syntax of the 912.Ic if 913command is: 914.Bd -unfilled -offset indent -compact 915.Ic if Ar list 916.Ic then Ar list 917.Oo Ic elif Ar list 918.Ic then Ar list Oc Ar ... 919.Op Ic else Ar list 920.Ic fi 921.Ed 922.Pp 923The syntax of the 924.Ic while 925command is: 926.Bd -unfilled -offset indent -compact 927.Ic while Ar list 928.Ic do Ar list 929.Ic done 930.Ed 931.Pp 932The two lists are executed repeatedly while the exit status of the 933first list is zero. 934The 935.Ic until 936command is similar, but has the word 937.Ic until 938in place of 939.Ic while , 940which causes it to 941repeat until the exit status of the first list is zero. 942.Pp 943The syntax of the 944.Ic for 945command is: 946.Bd -unfilled -offset indent -compact 947.Ic for Ar variable Op Ic in Ar word ... 948.Ic do Ar list 949.Ic done 950.Ed 951.Pp 952If 953.Ic in 954and the following words are omitted, 955.Ic in Li \&"$@\&" 956is used instead. 957The words are expanded, and then the list is executed 958repeatedly with the variable set to each word in turn. 959The 960.Ic do 961and 962.Ic done 963commands may be replaced with 964.Ql { 965and 966.Ql } . 967.Pp 968The syntax of the 969.Ic break 970and 971.Ic continue 972commands is: 973.D1 Ic break Op Ar num 974.D1 Ic continue Op Ar num 975.Pp 976The 977.Ic break 978command terminates the 979.Ar num 980innermost 981.Ic for 982or 983.Ic while 984loops. 985The 986.Ic continue 987command continues with the next iteration of the innermost loop. 988These are implemented as special built-in commands. 989.Pp 990The syntax of the 991.Ic case 992command is: 993.Bd -unfilled -offset indent -compact 994.Ic case Ar word Ic in 995.Ar pattern Ns Li ) Ar list Li ;; 996.Ar ... 997.Ic esac 998.Ed 999.Pp 1000The pattern can actually be one or more patterns 1001(see 1002.Sx Shell Patterns 1003described later), 1004separated by 1005.Ql \&| 1006characters. 1007Tilde expansion, parameter expansion, command substitution, 1008arithmetic expansion and quote removal are applied to the word. 1009Then, each pattern is expanded in turn using tilde expansion, 1010parameter expansion, command substitution and arithmetic expansion and 1011the expanded form of the word is checked against it. 1012If a match is found, the corresponding list is executed. 1013If the selected list is terminated by the control operator 1014.Ql ;& 1015instead of 1016.Ql ;; , 1017execution continues with the next list, 1018continuing until a list terminated with 1019.Ql ;; 1020or the end of the 1021.Ic case 1022command. 1023The exit code of the 1024.Ic case 1025command is the exit code of the last command executed in the list or 1026zero if no patterns were matched. 1027.Ss Grouping Commands Together 1028Commands may be grouped by writing either 1029.Pp 1030.D1 Li \&( Ns Ar list Ns Li \%) 1031.Pp 1032or 1033.Pp 1034.D1 Li { Ar list Ns Li \&; } 1035.Pp 1036The first form executes the commands in a subshell environment. 1037A subshell environment has its own copy of: 1038.Bl -enum 1039.It 1040The current working directory as set by 1041.Ic cd . 1042.It 1043The file creation mask as set by 1044.Ic umask . 1045.It 1046Resource limits as set by 1047.Ic ulimit . 1048.It 1049References to open files. 1050.It 1051Traps as set by 1052.Ic trap . 1053.It 1054Known jobs. 1055.It 1056Positional parameters and variables. 1057.It 1058Shell options. 1059.It 1060Shell functions. 1061.It 1062Shell aliases. 1063.El 1064.Pp 1065These are copied from the parent shell environment, 1066except that trapped (but not ignored) signals are reset to the default action 1067and known jobs are cleared. 1068Any changes do not affect the parent shell environment. 1069.Pp 1070A subshell environment may be implemented as a child process or differently. 1071If job control is enabled in an interactive shell, 1072commands grouped in parentheses can be suspended and continued as a unit. 1073.Pp 1074For compatibility with other shells, 1075two open parentheses in sequence should be separated by whitespace. 1076.Pp 1077The second form never forks another shell, 1078so it is slightly more efficient. 1079Grouping commands together this way allows the user to 1080redirect their output as though they were one program: 1081.Bd -literal -offset indent 1082{ echo -n "hello"; echo " world"; } > greeting 1083.Ed 1084.Ss Functions 1085The syntax of a function definition is 1086.Pp 1087.D1 Ar name Li \&( \&) Ar command 1088.Pp 1089A function definition is an executable statement; when 1090executed it installs a function named 1091.Ar name 1092and returns an 1093exit status of zero. 1094The 1095.Ar command 1096is normally a list 1097enclosed between 1098.Ql { 1099and 1100.Ql } . 1101.Pp 1102Variables may be declared to be local to a function by 1103using the 1104.Ic local 1105command. 1106This should appear as the first statement of a function, 1107and the syntax is: 1108.Pp 1109.D1 Ic local Oo Ar variable ... Oc Op Fl 1110.Pp 1111The 1112.Ic local 1113command is implemented as a built-in command. 1114.Pp 1115When a variable is made local, it inherits the initial 1116value and exported and readonly flags from the variable 1117with the same name in the surrounding scope, if there is 1118one. 1119Otherwise, the variable is initially unset. 1120The shell 1121uses dynamic scoping, so that if the variable 1122.Va x 1123is made local to function 1124.Em f , 1125which then calls function 1126.Em g , 1127references to the variable 1128.Va x 1129made inside 1130.Em g 1131will refer to the variable 1132.Va x 1133declared inside 1134.Em f , 1135not to the global variable named 1136.Va x . 1137.Pp 1138The only special parameter that can be made local is 1139.Ql - . 1140Making 1141.Ql - 1142local causes any shell options that are 1143changed via the 1144.Ic set 1145command inside the function to be 1146restored to their original values when the function 1147returns. 1148.Pp 1149The syntax of the 1150.Ic return 1151command is 1152.Pp 1153.D1 Ic return Op Ar exitstatus 1154.Pp 1155It terminates the current executional scope, returning from the previous 1156nested function, sourced script, or shell instance, in that order. 1157The 1158.Ic return 1159command is implemented as a special built-in command. 1160.Ss Variables and Parameters 1161The shell maintains a set of parameters. 1162A parameter 1163denoted by a name is called a variable. 1164When starting up, 1165the shell turns all the environment variables into shell 1166variables. 1167New variables can be set using the form 1168.Pp 1169.D1 Ar name Ns = Ns Ar value 1170.Pp 1171Variables set by the user must have a name consisting solely 1172of alphabetics, numerics, and underscores. 1173The first letter of a variable name must not be numeric. 1174A parameter can also be denoted by a number 1175or a special character as explained below. 1176.Pp 1177Assignments are expanded differently from other words: 1178tilde expansion is also performed after the equals sign and after any colon 1179and usernames are also terminated by colons, 1180and field splitting and pathname expansion are not performed. 1181.Pp 1182This special expansion applies not only to assignments that form a simple 1183command by themselves or precede a command word, 1184but also to words passed to the 1185.Ic export , 1186.Ic local 1187or 1188.Ic readonly 1189built-in commands that have this form. 1190For this, the builtin's name must be literal 1191(not the result of an expansion) 1192and may optionally be preceded by one or more literal instances of 1193.Ic command 1194without options. 1195.Ss Positional Parameters 1196A positional parameter is a parameter denoted by a number greater than zero. 1197The shell sets these initially to the values of its command line 1198arguments that follow the name of the shell script. 1199The 1200.Ic set 1201built-in command can also be used to set or reset them. 1202.Ss Special Parameters 1203Special parameters are parameters denoted by a single special character 1204or the digit zero. 1205They are shown in the following list, exactly as they would appear in input 1206typed by the user or in the source of a shell script. 1207.Bl -hang 1208.It Li $* 1209Expands to the positional parameters, starting from one. 1210When 1211the expansion occurs within a double-quoted string 1212it expands to a single field with the value of each parameter 1213separated by the first character of the 1214.Va IFS 1215variable, 1216or by a space if 1217.Va IFS 1218is unset. 1219.It Li $@ 1220Expands to the positional parameters, starting from one. 1221When 1222the expansion occurs within double-quotes, each positional 1223parameter expands as a separate argument. 1224If there are no positional parameters, the 1225expansion of 1226.Li @ 1227generates zero arguments, even when 1228.Li @ 1229is double-quoted. 1230What this basically means, for example, is 1231if 1232.Li $1 1233is 1234.Dq Li abc 1235and 1236.Li $2 1237is 1238.Dq Li "def ghi" , 1239then 1240.Li \&"$@\&" 1241expands to 1242the two arguments: 1243.Bd -literal -offset indent 1244"abc" "def ghi" 1245.Ed 1246.It Li $# 1247Expands to the number of positional parameters. 1248.It Li $? 1249Expands to the exit status of the most recent pipeline. 1250.It Li $- 1251(hyphen) Expands to the current option flags (the single-letter 1252option names concatenated into a string) as specified on 1253invocation, by the 1254.Ic set 1255built-in command, or implicitly 1256by the shell. 1257.It Li $$ 1258Expands to the process ID of the invoked shell. 1259A subshell 1260retains the same value of 1261.Va $ 1262as its parent. 1263.It Li $! 1264Expands to the process ID of the most recent background 1265command executed from the current shell. 1266For a 1267pipeline, the process ID is that of the last command in the 1268pipeline. 1269If this parameter is referenced, the shell will remember 1270the process ID and its exit status until the 1271.Ic wait 1272built-in command reports completion of the process. 1273.It Li $0 1274(zero) Expands to the name of the shell script if passed on the command line, 1275the 1276.Ar name 1277operand if given (with 1278.Fl c ) 1279or otherwise argument 0 passed to the shell. 1280.El 1281.Ss Special Variables 1282The following variables are set by the shell or 1283have special meaning to it: 1284.Bl -tag -width ".Va HISTSIZE" 1285.It Va CDPATH 1286The search path used with the 1287.Ic cd 1288built-in. 1289.It Va EDITOR 1290The fallback editor used with the 1291.Ic fc 1292built-in. 1293If not set, the default editor is 1294.Xr ed 1 . 1295.It Va FCEDIT 1296The default editor used with the 1297.Ic fc 1298built-in. 1299.It Va HISTSIZE 1300The number of previous commands that are accessible. 1301.It Va HOME 1302The user's home directory, 1303used in tilde expansion and as a default directory for the 1304.Ic cd 1305built-in. 1306.It Va IFS 1307Input Field Separators. 1308The default value is 1309.Aq space , 1310.Aq tab , 1311and 1312.Aq newline 1313in that order. 1314This default also applies if 1315.Va IFS 1316is unset, but not if it is set to the empty string. 1317See the 1318.Sx White Space Splitting 1319section for more details. 1320.It Va LINENO 1321The current line number in the script or function. 1322.It Va MAIL 1323The name of a mail file, that will be checked for the arrival of new 1324mail. 1325Overridden by 1326.Va MAILPATH . 1327.It Va MAILPATH 1328A colon 1329.Pq Ql \&: 1330separated list of file names, for the shell to check for incoming 1331mail. 1332This variable overrides the 1333.Va MAIL 1334setting. 1335There is a maximum of 10 mailboxes that can be monitored at once. 1336.It Va PATH 1337The default search path for executables. 1338See the 1339.Sx Path Search 1340section for details. 1341.It Va PPID 1342The parent process ID of the invoked shell. 1343This is set at startup 1344unless this variable is in the environment. 1345A later change of parent process ID is not reflected. 1346A subshell retains the same value of 1347.Va PPID . 1348.It Va PS1 1349The primary prompt string, which defaults to 1350.Dq Li "$ " , 1351unless you are the superuser, in which case it defaults to 1352.Dq Li "# " . 1353.Va PS1 1354may include any of the following formatting sequences, 1355which are replaced by the given information: 1356.Bl -tag -width indent 1357.It Li \eH 1358The local hostname. 1359.It Li \eh 1360The fully-qualified hostname. 1361.It Li \eW 1362The final component of the current working directory. 1363.It Li \ew 1364The entire path of the current working directory. 1365.It Li \e$ 1366Superuser status. 1367.Dq Li "$ " 1368for normal users and 1369.Dq Li "# " 1370for superusers. 1371.It Li \e\e 1372A literal backslash. 1373.El 1374.It Va PS2 1375The secondary prompt string, which defaults to 1376.Dq Li "> " . 1377.Va PS2 1378may include any of the formatting sequences from 1379.Va PS1 . 1380.It Va PS4 1381The prefix for the trace output (if 1382.Fl x 1383is active). 1384The default is 1385.Dq Li "+ " . 1386.El 1387.Ss Word Expansions 1388This clause describes the various expansions that are 1389performed on words. 1390Not all expansions are performed on 1391every word, as explained later. 1392.Pp 1393Tilde expansions, parameter expansions, command substitutions, 1394arithmetic expansions, and quote removals that occur within 1395a single word expand to a single field. 1396It is only field 1397splitting or pathname expansion that can create multiple 1398fields from a single word. 1399The single exception to this rule is 1400the expansion of the special parameter 1401.Va @ 1402within double-quotes, 1403as was described above. 1404.Pp 1405The order of word expansion is: 1406.Bl -enum 1407.It 1408Tilde Expansion, Parameter Expansion, Command Substitution, 1409Arithmetic Expansion (these all occur at the same time). 1410.It 1411Field Splitting is performed on fields generated by step (1) 1412unless the 1413.Va IFS 1414variable is null. 1415.It 1416Pathname Expansion (unless the 1417.Fl f 1418option is in effect). 1419.It 1420Quote Removal. 1421.El 1422.Pp 1423The 1424.Ql $ 1425character is used to introduce parameter expansion, command 1426substitution, or arithmetic expansion. 1427.Ss Tilde Expansion (substituting a user's home directory) 1428A word beginning with an unquoted tilde character 1429.Pq Ql ~ 1430is 1431subjected to tilde expansion. 1432All the characters up to a slash 1433.Pq Ql / 1434or the end of the word are treated as a username 1435and are replaced with the user's home directory. 1436If the 1437username is missing (as in 1438.Pa ~/foobar ) , 1439the tilde is replaced with the value of the 1440.Va HOME 1441variable (the current user's home directory). 1442.Ss Parameter Expansion 1443The format for parameter expansion is as follows: 1444.Pp 1445.D1 Li ${ Ns Ar expression Ns Li } 1446.Pp 1447where 1448.Ar expression 1449consists of all characters until the matching 1450.Ql } . 1451Any 1452.Ql } 1453escaped by a backslash or within a single-quoted or double-quoted 1454string, and characters in 1455embedded arithmetic expansions, command substitutions, and variable 1456expansions, are not examined in determining the matching 1457.Ql } . 1458If the variants with 1459.Ql + , 1460.Ql - , 1461.Ql = 1462or 1463.Ql ?\& 1464occur within a double-quoted string, 1465as an extension there may be unquoted parts 1466(via double-quotes inside the expansion); 1467.Ql } 1468within such parts are also not examined in determining the matching 1469.Ql } . 1470.Pp 1471The simplest form for parameter expansion is: 1472.Pp 1473.D1 Li ${ Ns Ar parameter Ns Li } 1474.Pp 1475The value, if any, of 1476.Ar parameter 1477is substituted. 1478.Pp 1479The parameter name or symbol can be enclosed in braces, which are 1480optional except for positional parameters with more than one digit or 1481when parameter is followed by a character that could be interpreted as 1482part of the name. 1483If a parameter expansion occurs inside double-quotes: 1484.Bl -enum 1485.It 1486Field splitting is not performed on the results of the 1487expansion, with the exception of the special parameter 1488.Va @ . 1489.It 1490Pathname expansion is not performed on the results of the 1491expansion. 1492.El 1493.Pp 1494In addition, a parameter expansion can be modified by using one of the 1495following formats. 1496.Bl -tag -width indent 1497.It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li } 1498Use Default Values. 1499If 1500.Ar parameter 1501is unset or null, the expansion of 1502.Ar word 1503is substituted; otherwise, the value of 1504.Ar parameter 1505is substituted. 1506.It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li } 1507Assign Default Values. 1508If 1509.Ar parameter 1510is unset or null, the expansion of 1511.Ar word 1512is assigned to 1513.Ar parameter . 1514In all cases, the 1515final value of 1516.Ar parameter 1517is substituted. 1518Quoting inside 1519.Ar word 1520does not prevent field splitting or pathname expansion. 1521Only variables, not positional 1522parameters or special parameters, can be 1523assigned in this way. 1524.It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li } 1525Indicate Error if Null or Unset. 1526If 1527.Ar parameter 1528is unset or null, the expansion of 1529.Ar word 1530(or a message indicating it is unset if 1531.Ar word 1532is omitted) is written to standard 1533error and the shell exits with a nonzero 1534exit status. 1535Otherwise, the value of 1536.Ar parameter 1537is substituted. 1538An 1539interactive shell need not exit. 1540.It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li } 1541Use Alternate Value. 1542If 1543.Ar parameter 1544is unset or null, null is substituted; 1545otherwise, the expansion of 1546.Ar word 1547is substituted. 1548.El 1549.Pp 1550In the parameter expansions shown previously, use of the colon in the 1551format results in a test for a parameter that is unset or null; omission 1552of the colon results in a test for a parameter that is only unset. 1553.Pp 1554The 1555.Ar word 1556inherits the type of quoting 1557(unquoted, double-quoted or here-document) 1558from the surroundings, 1559with the exception that a backslash that quotes a closing brace is removed 1560during quote removal. 1561.Bl -tag -width indent 1562.It Li ${# Ns Ar parameter Ns Li } 1563String Length. 1564The length in characters of 1565the value of 1566.Ar parameter . 1567.El 1568.Pp 1569The following four varieties of parameter expansion provide for substring 1570processing. 1571In each case, pattern matching notation 1572(see 1573.Sx Shell Patterns ) , 1574rather than regular expression notation, 1575is used to evaluate the patterns. 1576If parameter is one of the special parameters 1577.Va * 1578or 1579.Va @ , 1580the result of the expansion is unspecified. 1581Enclosing the full parameter expansion string in double-quotes does not 1582cause the following four varieties of pattern characters to be quoted, 1583whereas quoting characters within the braces has this effect. 1584.Bl -tag -width indent 1585.It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li } 1586Remove Smallest Suffix Pattern. 1587The 1588.Ar word 1589is expanded to produce a pattern. 1590The 1591parameter expansion then results in 1592.Ar parameter , 1593with the smallest portion of the 1594suffix matched by the pattern deleted. 1595.It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li } 1596Remove Largest Suffix Pattern. 1597The 1598.Ar word 1599is expanded to produce a pattern. 1600The 1601parameter expansion then results in 1602.Ar parameter , 1603with the largest portion of the 1604suffix matched by the pattern deleted. 1605.It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li } 1606Remove Smallest Prefix Pattern. 1607The 1608.Ar word 1609is expanded to produce a pattern. 1610The 1611parameter expansion then results in 1612.Ar parameter , 1613with the smallest portion of the 1614prefix matched by the pattern deleted. 1615.It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li } 1616Remove Largest Prefix Pattern. 1617The 1618.Ar word 1619is expanded to produce a pattern. 1620The 1621parameter expansion then results in 1622.Ar parameter , 1623with the largest portion of the 1624prefix matched by the pattern deleted. 1625.El 1626.Ss Command Substitution 1627Command substitution allows the output of a command to be substituted in 1628place of the command name itself. 1629Command substitution occurs when 1630the command is enclosed as follows: 1631.Pp 1632.D1 Li $( Ns Ar command Ns Li )\& 1633.Pp 1634or the backquoted version: 1635.Pp 1636.D1 Li ` Ns Ar command Ns Li ` 1637.Pp 1638The shell expands the command substitution by executing command 1639and replacing the command substitution 1640with the standard output of the command, 1641removing sequences of one or more newlines at the end of the substitution. 1642Embedded newlines before the end of the output are not removed; 1643however, during field splitting, they may be translated into spaces 1644depending on the value of 1645.Va IFS 1646and the quoting that is in effect. 1647The command is executed in a subshell environment, 1648except that the built-in commands 1649.Ic jobid , 1650.Ic jobs , 1651and 1652.Ic trap 1653return information about the parent shell environment 1654and 1655.Ic times 1656returns information about the same process 1657if they are the only command in a command substitution. 1658.Pp 1659If a command substitution of the 1660.Li $( 1661form begins with a subshell, 1662the 1663.Li $( 1664and 1665.Li (\& 1666must be separated by whitespace 1667to avoid ambiguity with arithmetic expansion. 1668.Ss Arithmetic Expansion 1669Arithmetic expansion provides a mechanism for evaluating an arithmetic 1670expression and substituting its value. 1671The format for arithmetic expansion is as follows: 1672.Pp 1673.D1 Li $(( Ns Ar expression Ns Li )) 1674.Pp 1675The 1676.Ar expression 1677is treated as if it were in double-quotes, except 1678that a double-quote inside the expression is not treated specially. 1679The 1680shell expands all tokens in the 1681.Ar expression 1682for parameter expansion, 1683command substitution, 1684arithmetic expansion 1685and quote removal. 1686.Pp 1687The allowed expressions are a subset of C expressions, 1688summarized below. 1689.Bl -tag -width "Variables" -offset indent 1690.It Values 1691All values are of type 1692.Ft intmax_t . 1693.It Constants 1694Decimal, octal (starting with 1695.Li 0 ) 1696and hexadecimal (starting with 1697.Li 0x ) 1698integer constants. 1699.It Variables 1700Shell variables can be read and written 1701and contain integer constants. 1702.It Unary operators 1703.Li "! ~ + -" 1704.It Binary operators 1705.Li "* / % + - << >> < <= > >= == != & ^ | && ||" 1706.It Assignment operators 1707.Li "= += -= *= /= %= <<= >>= &= ^= |=" 1708.It Conditional operator 1709.Li "? :" 1710.El 1711.Pp 1712The result of the expression is substituted in decimal. 1713.Ss White Space Splitting (Field Splitting) 1714In certain contexts, 1715after parameter expansion, command substitution, and 1716arithmetic expansion the shell scans the results of 1717expansions and substitutions that did not occur in double-quotes for 1718field splitting and multiple fields can result. 1719.Pp 1720Characters in 1721.Va IFS 1722that are whitespace 1723.Po 1724.Aq space , 1725.Aq tab , 1726and 1727.Aq newline 1728.Pc 1729are treated differently from other characters in 1730.Va IFS . 1731.Pp 1732Whitespace in 1733.Va IFS 1734at the beginning or end of a word is discarded. 1735.Pp 1736Subsequently, a field is delimited by either 1737.Bl -enum 1738.It 1739a non-whitespace character in 1740.Va IFS 1741with any whitespace in 1742.Va IFS 1743surrounding it, or 1744.It 1745one or more whitespace characters in 1746.Va IFS . 1747.El 1748.Pp 1749If a word ends with a non-whitespace character in 1750.Va IFS , 1751there is no empty field after this character. 1752.Pp 1753If no field is delimited, the word is discarded. 1754In particular, if a word consists solely of an unquoted substitution 1755and the result of the substitution is null, 1756it is removed by field splitting even if 1757.Va IFS 1758is null. 1759.Ss Pathname Expansion (File Name Generation) 1760Unless the 1761.Fl f 1762option is set, 1763file name generation is performed 1764after word splitting is complete. 1765Each word is 1766viewed as a series of patterns, separated by slashes. 1767The 1768process of expansion replaces the word with the names of 1769all existing files whose names can be formed by replacing 1770each pattern with a string that matches the specified pattern. 1771There are two restrictions on this: first, a pattern cannot match 1772a string containing a slash, and second, 1773a pattern cannot match a string starting with a period 1774unless the first character of the pattern is a period. 1775The next section describes the patterns used for 1776Pathname Expansion, 1777the four varieties of parameter expansion for substring processing and the 1778.Ic case 1779command. 1780.Ss Shell Patterns 1781A pattern consists of normal characters, which match themselves, 1782and meta-characters. 1783The meta-characters are 1784.Ql * , 1785.Ql \&? , 1786and 1787.Ql \&[ . 1788These characters lose their special meanings if they are quoted. 1789When command or variable substitution is performed and the dollar sign 1790or back quotes are not double-quoted, the value of the 1791variable or the output of the command is scanned for these 1792characters and they are turned into meta-characters. 1793.Pp 1794An asterisk 1795.Pq Ql * 1796matches any string of characters. 1797A question mark 1798.Pq Ql \&? 1799matches any single character. 1800A left bracket 1801.Pq Ql \&[ 1802introduces a character class. 1803The end of the character class is indicated by a 1804.Ql \&] ; 1805if the 1806.Ql \&] 1807is missing then the 1808.Ql \&[ 1809matches a 1810.Ql \&[ 1811rather than introducing a character class. 1812A character class matches any of the characters between the square brackets. 1813A locale-dependent range of characters may be specified using a minus sign. 1814A named class of characters (see 1815.Xr wctype 3 ) 1816may be specified by surrounding the name with 1817.Ql \&[: 1818and 1819.Ql :\&] . 1820For example, 1821.Ql \&[\&[:alpha:\&]\&] 1822is a shell pattern that matches a single letter. 1823The character class may be complemented by making an exclamation point 1824.Pq Ql !\& 1825the first character of the character class. 1826A caret 1827.Pq Ql ^ 1828has the same effect but is non-standard. 1829.Pp 1830To include a 1831.Ql \&] 1832in a character class, make it the first character listed 1833(after the 1834.Ql \&! 1835or 1836.Ql ^ , 1837if any). 1838To include a 1839.Ql - , 1840make it the first or last character listed. 1841.Ss Built-in Commands 1842This section lists the built-in commands. 1843.Bl -tag -width indent 1844.It Ic \&: 1845A null command that returns a 0 (true) exit value. 1846.It Ic \&. Ar file 1847The commands in the specified file are read and executed by the shell. 1848The 1849.Ic return 1850command may be used to return to the 1851.Ic \&. 1852command's caller. 1853If 1854.Ar file 1855contains any 1856.Ql / 1857characters, it is used as is. 1858Otherwise, the shell searches the 1859.Va PATH 1860for the file. 1861If it is not found in the 1862.Va PATH , 1863it is sought in the current working directory. 1864.It Ic \&[ 1865A built-in equivalent of 1866.Xr test 1 . 1867.It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc Ar ... Oc 1868If 1869.Ar name Ns = Ns Ar string 1870is specified, the shell defines the alias 1871.Ar name 1872with value 1873.Ar string . 1874If just 1875.Ar name 1876is specified, the value of the alias 1877.Ar name 1878is printed. 1879With no arguments, the 1880.Ic alias 1881built-in command prints the names and values of all defined aliases 1882(see 1883.Ic unalias ) . 1884Alias values are written with appropriate quoting so that they are 1885suitable for re-input to the shell. 1886Also see the 1887.Sx Aliases 1888subsection. 1889.It Ic bg Op Ar job ... 1890Continue the specified jobs 1891(or the current job if no jobs are given) 1892in the background. 1893.It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc 1894List or alter key bindings for the line editor. 1895This command is documented in 1896.Xr editrc 5 . 1897.It Ic break Op Ar num 1898See the 1899.Sx Flow-Control Constructs 1900subsection. 1901.It Ic builtin Ar cmd Op Ar arg ... 1902Execute the specified built-in command, 1903.Ar cmd . 1904This is useful when the user wishes to override a shell function 1905with the same name as a built-in command. 1906.It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory 1907Switch to the specified 1908.Ar directory , 1909or to the directory specified in the 1910.Va HOME 1911environment variable if no 1912.Ar directory 1913is specified. 1914If 1915.Ar directory 1916does not begin with 1917.Pa / , \&. , 1918or 1919.Pa .. , 1920then the directories listed in the 1921.Va CDPATH 1922variable will be 1923searched for the specified 1924.Ar directory . 1925If 1926.Va CDPATH 1927is unset, the current directory is searched. 1928The format of 1929.Va CDPATH 1930is the same as that of 1931.Va PATH . 1932In an interactive shell, 1933the 1934.Ic cd 1935command will print out the name of the directory 1936that it actually switched to 1937if this is different from the name that the user gave. 1938These may be different either because the 1939.Va CDPATH 1940mechanism was used or because a symbolic link was crossed. 1941.Pp 1942If the 1943.Fl P 1944option is specified, 1945.Pa .. 1946is handled physically and symbolic links are resolved before 1947.Pa .. 1948components are processed. 1949If the 1950.Fl L 1951option is specified, 1952.Pa .. 1953is handled logically. 1954This is the default. 1955.Pp 1956The 1957.Fl e 1958option causes 1959.Ic cd 1960to return exit status 1 if the full pathname of the new directory 1961cannot be determined reliably or at all. 1962Normally this is not considered an error, 1963although a warning is printed. 1964.It Ic chdir 1965A synonym for the 1966.Ic cd 1967built-in command. 1968.It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ... 1969.It Ic command Oo Fl p Oc Fl v Ar utility 1970.It Ic command Oo Fl p Oc Fl V Ar utility 1971The first form of invocation executes the specified 1972.Ar utility , 1973ignoring shell functions in the search. 1974If 1975.Ar utility 1976is a special builtin, 1977it is executed as if it were a regular builtin. 1978.Pp 1979If the 1980.Fl p 1981option is specified, the command search is performed using a 1982default value of 1983.Va PATH 1984that is guaranteed to find all of the standard utilities. 1985.Pp 1986If the 1987.Fl v 1988option is specified, 1989.Ar utility 1990is not executed but a description of its interpretation by the shell is 1991printed. 1992For ordinary commands the output is the path name; for shell built-in 1993commands, shell functions and keywords only the name is written. 1994Aliases are printed as 1995.Dq Ic alias Ar name Ns = Ns Ar value . 1996.Pp 1997The 1998.Fl V 1999option is identical to 2000.Fl v 2001except for the output. 2002It prints 2003.Dq Ar utility Ic is Ar description 2004where 2005.Ar description 2006is either 2007the path name to 2008.Ar utility , 2009a special shell builtin, 2010a shell builtin, 2011a shell function, 2012a shell keyword 2013or 2014an alias for 2015.Ar value . 2016.It Ic continue Op Ar num 2017See the 2018.Sx Flow-Control Constructs 2019subsection. 2020.It Ic echo Oo Fl e | n Oc Op Ar string ... 2021Print a space-separated list of the arguments to the standard output 2022and append a newline character. 2023.Bl -tag -width indent 2024.It Fl n 2025Suppress the output of the trailing newline. 2026.It Fl e 2027Process C-style backslash escape sequences. 2028The 2029.Ic echo 2030command understands the following character escapes: 2031.Bl -tag -width indent 2032.It \ea 2033Alert (ring the terminal bell) 2034.It \eb 2035Backspace 2036.It \ec 2037Suppress the trailing newline (this has the side-effect of truncating the 2038line if it is not the last character) 2039.It \ee 2040The ESC character 2041.Tn ( ASCII 20420x1b) 2043.It \ef 2044Formfeed 2045.It \en 2046Newline 2047.It \er 2048Carriage return 2049.It \et 2050Horizontal tab 2051.It \ev 2052Vertical tab 2053.It \e\e 2054Literal backslash 2055.It \e0nnn 2056(Zero) The character whose octal value is 2057.Ar nnn 2058.El 2059.Pp 2060If 2061.Ar string 2062is not enclosed in quotes then the backslash itself must be escaped 2063with a backslash to protect it from the shell. 2064For example 2065.Bd -literal -offset indent 2066$ echo -e "a\evb" 2067a 2068 b 2069$ echo -e a\e\evb 2070a 2071 b 2072$ echo -e "a\e\eb" 2073a\eb 2074$ echo -e a\e\e\e\eb 2075a\eb 2076.Ed 2077.El 2078.Pp 2079Only one of the 2080.Fl e 2081and 2082.Fl n 2083options may be specified. 2084.It Ic eval Ar string ... 2085Concatenate all the arguments with spaces. 2086Then re-parse and execute the command. 2087.It Ic exec Op Ar command Op Ar arg ... 2088Unless 2089.Ar command 2090is omitted, 2091the shell process is replaced with the specified program 2092(which must be a real program, not a shell built-in command or function). 2093Any redirections on the 2094.Ic exec 2095command are marked as permanent, 2096so that they are not undone when the 2097.Ic exec 2098command finishes. 2099.It Ic exit Op Ar exitstatus 2100Terminate the shell process. 2101If 2102.Ar exitstatus 2103is given 2104it is used as the exit status of the shell. 2105Otherwise, if the shell is executing an 2106.Cm EXIT 2107trap, the exit status of the last command before the trap is used; 2108if the shell is executing a trap for a signal, 2109the shell exits by resending the signal to itself. 2110Otherwise, the exit status of the preceding command is used. 2111The exit status should be an integer between 0 and 255. 2112.It Ic export Ar name ... 2113.It Ic export Op Fl p 2114The specified names are exported so that they will 2115appear in the environment of subsequent commands. 2116The only way to un-export a variable is to 2117.Ic unset 2118it. 2119The shell allows the value of a variable to be set 2120at the same time as it is exported by writing 2121.Pp 2122.D1 Ic export Ar name Ns = Ns Ar value 2123.Pp 2124With no arguments the 2125.Ic export 2126command lists the names 2127of all exported variables. 2128If the 2129.Fl p 2130option is specified, the exported variables are printed as 2131.Dq Ic export Ar name Ns = Ns Ar value 2132lines, suitable for re-input to the shell. 2133.It Ic false 2134A null command that returns a non-zero (false) exit value. 2135.It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last 2136.It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last 2137.It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first 2138The 2139.Ic fc 2140built-in command lists, or edits and re-executes, 2141commands previously entered to an interactive shell. 2142.Bl -tag -width indent 2143.It Fl e Ar editor 2144Use the editor named by 2145.Ar editor 2146to edit the commands. 2147The 2148.Ar editor 2149string is a command name, 2150subject to search via the 2151.Va PATH 2152variable. 2153The value in the 2154.Va FCEDIT 2155variable is used as a default when 2156.Fl e 2157is not specified. 2158If 2159.Va FCEDIT 2160is null or unset, the value of the 2161.Va EDITOR 2162variable is used. 2163If 2164.Va EDITOR 2165is null or unset, 2166.Xr ed 1 2167is used as the editor. 2168.It Fl l No (ell) 2169List the commands rather than invoking 2170an editor on them. 2171The commands are written in the 2172sequence indicated by the 2173.Ar first 2174and 2175.Ar last 2176operands, as affected by 2177.Fl r , 2178with each command preceded by the command number. 2179.It Fl n 2180Suppress command numbers when listing with 2181.Fl l . 2182.It Fl r 2183Reverse the order of the commands listed 2184(with 2185.Fl l ) 2186or edited 2187(with neither 2188.Fl l 2189nor 2190.Fl s ) . 2191.It Fl s 2192Re-execute the command without invoking an editor. 2193.It Ar first 2194.It Ar last 2195Select the commands to list or edit. 2196The number of previous commands that can be accessed 2197are determined by the value of the 2198.Va HISTSIZE 2199variable. 2200The value of 2201.Ar first 2202or 2203.Ar last 2204or both are one of the following: 2205.Bl -tag -width indent 2206.It Oo Cm + Oc Ns Ar num 2207A positive number representing a command number; 2208command numbers can be displayed with the 2209.Fl l 2210option. 2211.It Fl Ar num 2212A negative decimal number representing the 2213command that was executed 2214.Ar num 2215of 2216commands previously. 2217For example, \-1 is the immediately previous command. 2218.It Ar string 2219A string indicating the most recently entered command 2220that begins with that string. 2221If the 2222.Ar old Ns = Ns Ar new 2223operand is not also specified with 2224.Fl s , 2225the string form of the first operand cannot contain an embedded equal sign. 2226.El 2227.El 2228.Pp 2229The following variables affect the execution of 2230.Ic fc : 2231.Bl -tag -width ".Va HISTSIZE" 2232.It Va FCEDIT 2233Name of the editor to use for history editing. 2234.It Va HISTSIZE 2235The number of previous commands that are accessible. 2236.El 2237.It Ic fg Op Ar job 2238Move the specified 2239.Ar job 2240or the current job to the foreground. 2241.It Ic getopts Ar optstring var 2242The 2243.Tn POSIX 2244.Ic getopts 2245command. 2246The 2247.Ic getopts 2248command deprecates the older 2249.Xr getopt 1 2250command. 2251The first argument should be a series of letters, each possibly 2252followed by a colon which indicates that the option takes an argument. 2253The specified variable is set to the parsed option. 2254The index of 2255the next argument is placed into the shell variable 2256.Va OPTIND . 2257If an option takes an argument, it is placed into the shell variable 2258.Va OPTARG . 2259If an invalid option is encountered, 2260.Ar var 2261is set to 2262.Ql \&? . 2263It returns a false value (1) when it encounters the end of the options. 2264.It Ic hash Oo Fl rv Oc Op Ar command ... 2265The shell maintains a hash table which remembers the locations of commands. 2266With no arguments whatsoever, the 2267.Ic hash 2268command prints out the contents of this table. 2269.Pp 2270With arguments, the 2271.Ic hash 2272command removes each specified 2273.Ar command 2274from the hash table (unless they are functions) and then locates it. 2275With the 2276.Fl v 2277option, 2278.Ic hash 2279prints the locations of the commands as it finds them. 2280The 2281.Fl r 2282option causes the 2283.Ic hash 2284command to delete all the entries in the hash table except for functions. 2285.It Ic jobid Op Ar job 2286Print the process IDs of the processes in the specified 2287.Ar job . 2288If the 2289.Ar job 2290argument is omitted, use the current job. 2291.It Ic jobs Oo Fl lps Oc Op Ar job ... 2292Print information about the specified jobs, or all jobs if no 2293.Ar job 2294argument is given. 2295The information printed includes job ID, status and command name. 2296.Pp 2297If the 2298.Fl l 2299option is specified, the PID of each job is also printed. 2300If the 2301.Fl p 2302option is specified, only the process IDs for the process group leaders 2303are printed, one per line. 2304If the 2305.Fl s 2306option is specified, only the PIDs of the job commands are printed, one per 2307line. 2308.It Ic kill 2309A built-in equivalent of 2310.Xr kill 1 2311that additionally supports sending signals to jobs. 2312.It Ic local Oo Ar variable ... Oc Op Fl 2313See the 2314.Sx Functions 2315subsection. 2316.It Ic printf 2317A built-in equivalent of 2318.Xr printf 1 . 2319.It Ic pwd Op Fl L | P 2320Print the path of the current directory. 2321The built-in command may 2322differ from the program of the same name because the 2323built-in command remembers what the current directory 2324is rather than recomputing it each time. 2325This makes 2326it faster. 2327However, if the current directory is 2328renamed, 2329the built-in version of 2330.Xr pwd 1 2331will continue to print the old name for the directory. 2332.Pp 2333If the 2334.Fl P 2335option is specified, symbolic links are resolved. 2336If the 2337.Fl L 2338option is specified, the shell's notion of the current directory 2339is printed (symbolic links are not resolved). 2340This is the default. 2341.It Ic read Oo Fl p Ar prompt Oc Oo 2342.Fl t Ar timeout Oc Oo Fl er Oc Ar variable ... 2343The 2344.Ar prompt 2345is printed if the 2346.Fl p 2347option is specified 2348and the standard input is a terminal. 2349Then a line is 2350read from the standard input. 2351The trailing newline 2352is deleted from the line and the line is split as 2353described in the section on 2354.Sx White Space Splitting (Field Splitting) 2355above, and 2356the pieces are assigned to the variables in order. 2357If there are more pieces than variables, the remaining 2358pieces (along with the characters in 2359.Va IFS 2360that separated them) 2361are assigned to the last variable. 2362If there are more variables than pieces, the remaining 2363variables are assigned the null string. 2364.Pp 2365Backslashes are treated specially, unless the 2366.Fl r 2367option is 2368specified. 2369If a backslash is followed by 2370a newline, the backslash and the newline will be 2371deleted. 2372If a backslash is followed by any other 2373character, the backslash will be deleted and the following 2374character will be treated as though it were not in 2375.Va IFS , 2376even if it is. 2377.Pp 2378If the 2379.Fl t 2380option is specified and the 2381.Ar timeout 2382elapses before a complete line of input is supplied, 2383the 2384.Ic read 2385command will return an exit status as if terminated by 2386.Dv SIGALRM 2387without assigning any values. 2388The 2389.Ar timeout 2390value may optionally be followed by one of 2391.Ql s , 2392.Ql m 2393or 2394.Ql h 2395to explicitly specify seconds, minutes or hours. 2396If none is supplied, 2397.Ql s 2398is assumed. 2399.Pp 2400The 2401.Fl e 2402option exists only for backward compatibility with older scripts. 2403.Pp 2404The exit status is 0 on success, 1 on end of file, 2405between 2 and 128 if an error occurs 2406and greater than 128 if a trapped signal interrupts 2407.Ic read . 2408.It Ic readonly Oo Fl p Oc Op Ar name ... 2409Each specified 2410.Ar name 2411is marked as read only, 2412so that it cannot be subsequently modified or unset. 2413The shell allows the value of a variable to be set 2414at the same time as it is marked read only 2415by using the following form: 2416.Pp 2417.D1 Ic readonly Ar name Ns = Ns Ar value 2418.Pp 2419With no arguments the 2420.Ic readonly 2421command lists the names of all read only variables. 2422If the 2423.Fl p 2424option is specified, the read-only variables are printed as 2425.Dq Ic readonly Ar name Ns = Ns Ar value 2426lines, suitable for re-input to the shell. 2427.It Ic return Op Ar exitstatus 2428See the 2429.Sx Functions 2430subsection. 2431.It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo 2432.Fl c Ar string Oc Op Fl - Ar arg ... 2433The 2434.Ic set 2435command performs three different functions: 2436.Bl -item 2437.It 2438With no arguments, it lists the values of all shell variables. 2439.It 2440If options are given, 2441either in short form or using the long 2442.Dq Fl /+o Ar longname 2443form, 2444it sets or clears the specified options as described in the section called 2445.Sx Argument List Processing . 2446.It 2447If the 2448.Dq Fl - 2449option is specified, 2450.Ic set 2451will replace the shell's positional parameters with the subsequent 2452arguments. 2453If no arguments follow the 2454.Dq Fl - 2455option, 2456all the positional parameters will be cleared, 2457which is equivalent to executing the command 2458.Dq Li "shift $#" . 2459The 2460.Dq Fl - 2461flag may be omitted when specifying arguments to be used 2462as positional replacement parameters. 2463This is not recommended, 2464because the first argument may begin with a dash 2465.Pq Ql - 2466or a plus 2467.Pq Ql + , 2468which the 2469.Ic set 2470command will interpret as a request to enable or disable options. 2471.El 2472.It Ic setvar Ar variable value 2473Assigns the specified 2474.Ar value 2475to the specified 2476.Ar variable . 2477The 2478.Ic setvar 2479command is intended to be used in functions that 2480assign values to variables whose names are passed as parameters. 2481In general it is better to write 2482.Dq Ar variable Ns = Ns Ar value 2483rather than using 2484.Ic setvar . 2485.It Ic shift Op Ar n 2486Shift the positional parameters 2487.Ar n 2488times, or once if 2489.Ar n 2490is not specified. 2491A shift sets the value of 2492.Li $1 2493to the value of 2494.Li $2 , 2495the value of 2496.Li $2 2497to the value of 2498.Li $3 , 2499and so on, 2500decreasing the value of 2501.Li $# 2502by one. 2503If there are zero positional parameters, shifting does not do anything. 2504.It Ic test 2505A built-in equivalent of 2506.Xr test 1 . 2507.It Ic times 2508Print the amount of time spent executing the shell process and its children. 2509The first output line shows the user and system times for the shell process 2510itself, the second one contains the user and system times for the 2511children. 2512.It Ic trap Oo Ar action Oc Ar signal ... 2513.It Ic trap Fl l 2514Cause the shell to parse and execute 2515.Ar action 2516when any specified 2517.Ar signal 2518is received. 2519The signals are specified by name or number. 2520In addition, the pseudo-signal 2521.Cm EXIT 2522may be used to specify an 2523.Ar action 2524that is performed when the shell terminates. 2525The 2526.Ar action 2527may be an empty string or a dash 2528.Pq Ql - ; 2529the former causes the specified signal to be ignored 2530and the latter causes the default action to be taken. 2531Omitting the 2532.Ar action 2533is another way to request the default action, for compatibility reasons this 2534usage is not recommended though. 2535In a subshell or utility environment, 2536the shell resets trapped (but not ignored) signals to the default action. 2537The 2538.Ic trap 2539command has no effect on signals that were ignored on entry to the shell. 2540.Pp 2541Option 2542.Fl l 2543causes the 2544.Ic trap 2545command to display a list of valid signal names. 2546.It Ic true 2547A null command that returns a 0 (true) exit value. 2548.It Ic type Op Ar name ... 2549Interpret each 2550.Ar name 2551as a command and print the resolution of the command search. 2552Possible resolutions are: 2553shell keyword, alias, special shell builtin, shell builtin, command, 2554tracked alias 2555and not found. 2556For aliases the alias expansion is printed; 2557for commands and tracked aliases 2558the complete pathname of the command is printed. 2559.It Ic ulimit Oo Fl HSabcdflmnstuv Oc Op Ar limit 2560Set or display resource limits (see 2561.Xr getrlimit 2 ) . 2562If 2563.Ar limit 2564is specified, the named resource will be set; 2565otherwise the current resource value will be displayed. 2566.Pp 2567If 2568.Fl H 2569is specified, the hard limits will be set or displayed. 2570While everybody is allowed to reduce a hard limit, 2571only the superuser can increase it. 2572The 2573.Fl S 2574option 2575specifies the soft limits instead. 2576When displaying limits, 2577only one of 2578.Fl S 2579or 2580.Fl H 2581can be given. 2582The default is to display the soft limits, 2583and to set both the hard and the soft limits. 2584.Pp 2585Option 2586.Fl a 2587causes the 2588.Ic ulimit 2589command to display all resources. 2590The parameter 2591.Ar limit 2592is not acceptable in this mode. 2593.Pp 2594The remaining options specify which resource value is to be 2595displayed or modified. 2596They are mutually exclusive. 2597.Bl -tag -width indent 2598.It Fl b Ar sbsize 2599The maximum size of socket buffer usage, in bytes. 2600.It Fl c Ar coredumpsize 2601The maximal size of core dump files, in 512-byte blocks. 2602.It Fl d Ar datasize 2603The maximal size of the data segment of a process, in kilobytes. 2604.It Fl f Ar filesize 2605The maximal size of a file, in 512-byte blocks. 2606.It Fl l Ar lockedmem 2607The maximal size of memory that can be locked by a process, in 2608kilobytes. 2609.It Fl m Ar memoryuse 2610The maximal resident set size of a process, in kilobytes. 2611.It Fl n Ar nofiles 2612The maximal number of descriptors that could be opened by a process. 2613.It Fl s Ar stacksize 2614The maximal size of the stack segment, in kilobytes. 2615.It Fl t Ar time 2616The maximal amount of CPU time to be used by each process, in seconds. 2617.It Fl u Ar userproc 2618The maximal number of simultaneous processes for this user ID. 2619.It Fl v Ar virtualmem 2620The maximal virtual size of a process, in kilobytes. 2621.El 2622.It Ic umask Oo Fl S Oc Op Ar mask 2623Set the file creation mask (see 2624.Xr umask 2 ) 2625to the octal or symbolic (see 2626.Xr chmod 1 ) 2627value specified by 2628.Ar mask . 2629If the argument is omitted, the current mask value is printed. 2630If the 2631.Fl S 2632option is specified, the output is symbolic, otherwise the output is octal. 2633.It Ic unalias Oo Fl a Oc Op Ar name ... 2634The specified alias names are removed. 2635If 2636.Fl a 2637is specified, all aliases are removed. 2638.It Ic unset Oo Fl fv Oc Ar name ... 2639The specified variables or functions are unset and unexported. 2640If the 2641.Fl v 2642option is specified or no options are given, the 2643.Ar name 2644arguments are treated as variable names. 2645If the 2646.Fl f 2647option is specified, the 2648.Ar name 2649arguments are treated as function names. 2650.It Ic wait Op Ar job ... 2651Wait for each specified 2652.Ar job 2653to complete and return the exit status of the last process in the 2654last specified 2655.Ar job . 2656If any 2657.Ar job 2658specified is unknown to the shell, it is treated as if it 2659were a known job that exited with exit status 127. 2660If no operands are given, wait for all jobs to complete 2661and return an exit status of zero. 2662.El 2663.Ss Commandline Editing 2664When 2665.Nm 2666is being used interactively from a terminal, the current command 2667and the command history 2668(see 2669.Ic fc 2670in 2671.Sx Built-in Commands ) 2672can be edited using 2673.Nm vi Ns -mode 2674command line editing. 2675This mode uses commands similar 2676to a subset of those described in the 2677.Xr vi 1 2678man page. 2679The command 2680.Dq Li "set -o vi" 2681(or 2682.Dq Li "set -V" ) 2683enables 2684.Nm vi Ns -mode 2685editing and places 2686.Nm 2687into 2688.Nm vi 2689insert mode. 2690With 2691.Nm vi Ns -mode 2692enabled, 2693.Nm 2694can be switched between insert mode and command mode by typing 2695.Aq ESC . 2696Hitting 2697.Aq return 2698while in command mode will pass the line to the shell. 2699.Pp 2700Similarly, the 2701.Dq Li "set -o emacs" 2702(or 2703.Dq Li "set -E" ) 2704command can be used to enable a subset of 2705.Nm emacs Ns -style 2706command line editing features. 2707.Sh ENVIRONMENT 2708The following environment variables affect the execution of 2709.Nm : 2710.Bl -tag -width ".Ev LANGXXXXXX" 2711.It Ev ENV 2712Initialization file for interactive shells. 2713.It Ev LANG , Ev LC_* 2714Locale settings. 2715These are inherited by children of the shell, 2716and is used in a limited manner by the shell itself. 2717.It Ev PWD 2718An absolute pathname for the current directory, 2719possibly containing symbolic links. 2720This is used and updated by the shell. 2721.It Ev TERM 2722The default terminal setting for the shell. 2723This is inherited by children of the shell, and is used in the history 2724editing modes. 2725.El 2726.Pp 2727Additionally, all environment variables are turned into shell variables 2728at startup, 2729which may affect the shell as described under 2730.Sx Special Variables . 2731.Sh FILES 2732.Bl -tag -width "/etc/suid_profileXX" -compact 2733.It Pa ~/.profile 2734User's login profile. 2735.It Pa /etc/profile 2736System login profile. 2737.It Pa /etc/shells 2738Shell database. 2739.It Pa /etc/suid_profile 2740Privileged shell profile. 2741.El 2742.Sh EXIT STATUS 2743Errors that are detected by the shell, such as a syntax error, will 2744cause the shell to exit with a non-zero exit status. 2745If the shell is not an interactive shell, the execution of the shell 2746file will be aborted. 2747Otherwise the shell will return the exit status of the last command 2748executed, or if the 2749.Ic exit 2750builtin is used with a numeric argument, it 2751will return the argument. 2752.Sh SEE ALSO 2753.Xr builtin 1 , 2754.Xr chsh 1 , 2755.Xr echo 1 , 2756.Xr ed 1 , 2757.Xr emacs 1 Pq Pa editors/emacs , 2758.Xr kill 1 , 2759.Xr printf 1 , 2760.Xr pwd 1 , 2761.Xr test 1 , 2762.Xr vi 1 , 2763.Xr execve 2 , 2764.Xr getrlimit 2 , 2765.Xr umask 2 , 2766.Xr wctype 3 , 2767.Xr editrc 5 , 2768.Xr shells 5 , 2769.Xr script 7 2770.Sh HISTORY 2771A 2772.Nm 2773command, the Thompson shell, appeared in 2774.At v1 . 2775It was superseded in 2776.At v7 2777by the Bourne shell, which inherited the name 2778.Nm . 2779.Pp 2780This version of 2781.Nm 2782was rewritten in 1989 under the 2783.Bx 2784license after the Bourne shell from 2785.At V.4 . 2786.Sh AUTHORS 2787This version of 2788.Nm 2789was originally written by 2790.An Kenneth Almquist . 2791.Sh BUGS 2792The 2793.Nm 2794utility does not recognize multibyte characters other than UTF-8. 2795Splitting using 2796.Va IFS 2797and the line editing library 2798.Xr editline 3 2799do not recognize multibyte characters. 2800.Pp 2801The characters generated by filename completion should probably be quoted 2802to ensure that the filename is still valid after the input line has been 2803processed. 2804