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 245805 2013-01-22 18:02:58Z joel $ 34.\" 35.Dd January 22, 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 1046References to open files. 1047.It 1048Traps as set by 1049.Ic trap . 1050.It 1051Known jobs. 1052.It 1053Positional parameters and variables. 1054.It 1055Shell options. 1056.It 1057Shell functions. 1058.It 1059Shell aliases. 1060.El 1061.Pp 1062These are copied from the parent shell environment, 1063except that trapped (but not ignored) signals are reset to the default action 1064and known jobs are cleared. 1065Any changes do not affect the parent shell environment. 1066.Pp 1067A subshell environment may be implemented as a child process or differently. 1068If job control is enabled in an interactive shell, 1069commands grouped in parentheses can be suspended and continued as a unit. 1070.Pp 1071The second form never forks another shell, 1072so it is slightly more efficient. 1073Grouping commands together this way allows the user to 1074redirect their output as though they were one program: 1075.Bd -literal -offset indent 1076{ echo -n "hello"; echo " world"; } > greeting 1077.Ed 1078.Ss Functions 1079The syntax of a function definition is 1080.Pp 1081.D1 Ar name Li \&( \&) Ar command 1082.Pp 1083A function definition is an executable statement; when 1084executed it installs a function named 1085.Ar name 1086and returns an 1087exit status of zero. 1088The 1089.Ar command 1090is normally a list 1091enclosed between 1092.Ql { 1093and 1094.Ql } . 1095.Pp 1096Variables may be declared to be local to a function by 1097using the 1098.Ic local 1099command. 1100This should appear as the first statement of a function, 1101and the syntax is: 1102.Pp 1103.D1 Ic local Oo Ar variable ... Oc Op Fl 1104.Pp 1105The 1106.Ic local 1107command is implemented as a built-in command. 1108.Pp 1109When a variable is made local, it inherits the initial 1110value and exported and readonly flags from the variable 1111with the same name in the surrounding scope, if there is 1112one. 1113Otherwise, the variable is initially unset. 1114The shell 1115uses dynamic scoping, so that if the variable 1116.Va x 1117is made local to function 1118.Em f , 1119which then calls function 1120.Em g , 1121references to the variable 1122.Va x 1123made inside 1124.Em g 1125will refer to the variable 1126.Va x 1127declared inside 1128.Em f , 1129not to the global variable named 1130.Va x . 1131.Pp 1132The only special parameter that can be made local is 1133.Ql - . 1134Making 1135.Ql - 1136local causes any shell options that are 1137changed via the 1138.Ic set 1139command inside the function to be 1140restored to their original values when the function 1141returns. 1142.Pp 1143The syntax of the 1144.Ic return 1145command is 1146.Pp 1147.D1 Ic return Op Ar exitstatus 1148.Pp 1149It terminates the current executional scope, returning from the previous 1150nested function, sourced script, or shell instance, in that order. 1151The 1152.Ic return 1153command is implemented as a special built-in command. 1154.Ss Variables and Parameters 1155The shell maintains a set of parameters. 1156A parameter 1157denoted by a name is called a variable. 1158When starting up, 1159the shell turns all the environment variables into shell 1160variables. 1161New variables can be set using the form 1162.Pp 1163.D1 Ar name Ns = Ns Ar value 1164.Pp 1165Variables set by the user must have a name consisting solely 1166of alphabetics, numerics, and underscores. 1167The first letter of a variable name must not be numeric. 1168A parameter can also be denoted by a number 1169or a special character as explained below. 1170.Pp 1171Assignments are expanded differently from other words: 1172tilde expansion is also performed after the equals sign and after any colon 1173and usernames are also terminated by colons, 1174and field splitting and pathname expansion are not performed. 1175.Pp 1176This special expansion applies not only to assignments that form a simple 1177command by themselves or precede a command word, 1178but also to words passed to the 1179.Ic export , 1180.Ic local 1181or 1182.Ic readonly 1183built-in commands that have this form. 1184For this, the builtin's name must be literal 1185(not the result of an expansion) 1186and may optionally be preceded by one or more literal instances of 1187.Ic command 1188without options. 1189.Ss Positional Parameters 1190A positional parameter is a parameter denoted by a number greater than zero. 1191The shell sets these initially to the values of its command line 1192arguments that follow the name of the shell script. 1193The 1194.Ic set 1195built-in command can also be used to set or reset them. 1196.Ss Special Parameters 1197Special parameters are parameters denoted by a single special character 1198or the digit zero. 1199They are shown in the following list, exactly as they would appear in input 1200typed by the user or in the source of a shell script. 1201.Bl -hang 1202.It Li $* 1203Expands to the positional parameters, starting from one. 1204When 1205the expansion occurs within a double-quoted string 1206it expands to a single field with the value of each parameter 1207separated by the first character of the 1208.Va IFS 1209variable, 1210or by a space if 1211.Va IFS 1212is unset. 1213.It Li $@ 1214Expands to the positional parameters, starting from one. 1215When 1216the expansion occurs within double-quotes, each positional 1217parameter expands as a separate argument. 1218If there are no positional parameters, the 1219expansion of 1220.Li @ 1221generates zero arguments, even when 1222.Li @ 1223is double-quoted. 1224What this basically means, for example, is 1225if 1226.Li $1 1227is 1228.Dq Li abc 1229and 1230.Li $2 1231is 1232.Dq Li "def ghi" , 1233then 1234.Li \&"$@\&" 1235expands to 1236the two arguments: 1237.Bd -literal -offset indent 1238"abc" "def ghi" 1239.Ed 1240.It Li $# 1241Expands to the number of positional parameters. 1242.It Li $? 1243Expands to the exit status of the most recent pipeline. 1244.It Li $- 1245(hyphen) Expands to the current option flags (the single-letter 1246option names concatenated into a string) as specified on 1247invocation, by the 1248.Ic set 1249built-in command, or implicitly 1250by the shell. 1251.It Li $$ 1252Expands to the process ID of the invoked shell. 1253A subshell 1254retains the same value of 1255.Va $ 1256as its parent. 1257.It Li $! 1258Expands to the process ID of the most recent background 1259command executed from the current shell. 1260For a 1261pipeline, the process ID is that of the last command in the 1262pipeline. 1263If this parameter is referenced, the shell will remember 1264the process ID and its exit status until the 1265.Ic wait 1266built-in command reports completion of the process. 1267.It Li $0 1268(zero) Expands to the name of the shell script if passed on the command line, 1269the 1270.Ar name 1271operand if given (with 1272.Fl c ) 1273or otherwise argument 0 passed to the shell. 1274.El 1275.Ss Special Variables 1276The following variables are set by the shell or 1277have special meaning to it: 1278.Bl -tag -width ".Va HISTSIZE" 1279.It Va CDPATH 1280The search path used with the 1281.Ic cd 1282built-in. 1283.It Va EDITOR 1284The fallback editor used with the 1285.Ic fc 1286built-in. 1287If not set, the default editor is 1288.Xr ed 1 . 1289.It Va FCEDIT 1290The default editor used with the 1291.Ic fc 1292built-in. 1293.It Va HISTSIZE 1294The number of previous commands that are accessible. 1295.It Va HOME 1296The user's home directory, 1297used in tilde expansion and as a default directory for the 1298.Ic cd 1299built-in. 1300.It Va IFS 1301Input Field Separators. 1302The default value is 1303.Aq space , 1304.Aq tab , 1305and 1306.Aq newline 1307in that order. 1308This default also applies if 1309.Va IFS 1310is unset, but not if it is set to the empty string. 1311See the 1312.Sx White Space Splitting 1313section for more details. 1314.It Va LINENO 1315The current line number in the script or function. 1316.It Va MAIL 1317The name of a mail file, that will be checked for the arrival of new 1318mail. 1319Overridden by 1320.Va MAILPATH . 1321.It Va MAILPATH 1322A colon 1323.Pq Ql \&: 1324separated list of file names, for the shell to check for incoming 1325mail. 1326This variable overrides the 1327.Va MAIL 1328setting. 1329There is a maximum of 10 mailboxes that can be monitored at once. 1330.It Va PATH 1331The default search path for executables. 1332See the 1333.Sx Path Search 1334section for details. 1335.It Va PPID 1336The parent process ID of the invoked shell. 1337This is set at startup 1338unless this variable is in the environment. 1339A later change of parent process ID is not reflected. 1340A subshell retains the same value of 1341.Va PPID . 1342.It Va PS1 1343The primary prompt string, which defaults to 1344.Dq Li "$ " , 1345unless you are the superuser, in which case it defaults to 1346.Dq Li "# " . 1347.It Va PS2 1348The secondary prompt string, which defaults to 1349.Dq Li "> " . 1350.It Va PS4 1351The prefix for the trace output (if 1352.Fl x 1353is active). 1354The default is 1355.Dq Li "+ " . 1356.El 1357.Ss Word Expansions 1358This clause describes the various expansions that are 1359performed on words. 1360Not all expansions are performed on 1361every word, as explained later. 1362.Pp 1363Tilde expansions, parameter expansions, command substitutions, 1364arithmetic expansions, and quote removals that occur within 1365a single word expand to a single field. 1366It is only field 1367splitting or pathname expansion that can create multiple 1368fields from a single word. 1369The single exception to this rule is 1370the expansion of the special parameter 1371.Va @ 1372within double-quotes, 1373as was described above. 1374.Pp 1375The order of word expansion is: 1376.Bl -enum 1377.It 1378Tilde Expansion, Parameter Expansion, Command Substitution, 1379Arithmetic Expansion (these all occur at the same time). 1380.It 1381Field Splitting is performed on fields generated by step (1) 1382unless the 1383.Va IFS 1384variable is null. 1385.It 1386Pathname Expansion (unless the 1387.Fl f 1388option is in effect). 1389.It 1390Quote Removal. 1391.El 1392.Pp 1393The 1394.Ql $ 1395character is used to introduce parameter expansion, command 1396substitution, or arithmetic expansion. 1397.Ss Tilde Expansion (substituting a user's home directory) 1398A word beginning with an unquoted tilde character 1399.Pq Ql ~ 1400is 1401subjected to tilde expansion. 1402All the characters up to a slash 1403.Pq Ql / 1404or the end of the word are treated as a username 1405and are replaced with the user's home directory. 1406If the 1407username is missing (as in 1408.Pa ~/foobar ) , 1409the tilde is replaced with the value of the 1410.Va HOME 1411variable (the current user's home directory). 1412.Ss Parameter Expansion 1413The format for parameter expansion is as follows: 1414.Pp 1415.D1 Li ${ Ns Ar expression Ns Li } 1416.Pp 1417where 1418.Ar expression 1419consists of all characters until the matching 1420.Ql } . 1421Any 1422.Ql } 1423escaped by a backslash or within a single-quoted or double-quoted 1424string, and characters in 1425embedded arithmetic expansions, command substitutions, and variable 1426expansions, are not examined in determining the matching 1427.Ql } . 1428If the variants with 1429.Ql + , 1430.Ql - , 1431.Ql = 1432or 1433.Ql ?\& 1434occur within a double-quoted string, 1435as an extension there may be unquoted parts 1436(via double-quotes inside the expansion); 1437.Ql } 1438within such parts are also not examined in determining the matching 1439.Ql } . 1440.Pp 1441The simplest form for parameter expansion is: 1442.Pp 1443.D1 Li ${ Ns Ar parameter Ns Li } 1444.Pp 1445The value, if any, of 1446.Ar parameter 1447is substituted. 1448.Pp 1449The parameter name or symbol can be enclosed in braces, which are 1450optional except for positional parameters with more than one digit or 1451when parameter is followed by a character that could be interpreted as 1452part of the name. 1453If a parameter expansion occurs inside double-quotes: 1454.Bl -enum 1455.It 1456Field splitting is not performed on the results of the 1457expansion, with the exception of the special parameter 1458.Va @ . 1459.It 1460Pathname expansion is not performed on the results of the 1461expansion. 1462.El 1463.Pp 1464In addition, a parameter expansion can be modified by using one of the 1465following formats. 1466.Bl -tag -width indent 1467.It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li } 1468Use Default Values. 1469If 1470.Ar parameter 1471is unset or null, the expansion of 1472.Ar word 1473is substituted; otherwise, the value of 1474.Ar parameter 1475is substituted. 1476.It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li } 1477Assign Default Values. 1478If 1479.Ar parameter 1480is unset or null, the expansion of 1481.Ar word 1482is assigned to 1483.Ar parameter . 1484In all cases, the 1485final value of 1486.Ar parameter 1487is substituted. 1488Quoting inside 1489.Ar word 1490does not prevent field splitting or pathname expansion. 1491Only variables, not positional 1492parameters or special parameters, can be 1493assigned in this way. 1494.It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li } 1495Indicate Error if Null or Unset. 1496If 1497.Ar parameter 1498is unset or null, the expansion of 1499.Ar word 1500(or a message indicating it is unset if 1501.Ar word 1502is omitted) is written to standard 1503error and the shell exits with a nonzero 1504exit status. 1505Otherwise, the value of 1506.Ar parameter 1507is substituted. 1508An 1509interactive shell need not exit. 1510.It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li } 1511Use Alternate Value. 1512If 1513.Ar parameter 1514is unset or null, null is substituted; 1515otherwise, the expansion of 1516.Ar word 1517is substituted. 1518.El 1519.Pp 1520In the parameter expansions shown previously, use of the colon in the 1521format results in a test for a parameter that is unset or null; omission 1522of the colon results in a test for a parameter that is only unset. 1523.Pp 1524The 1525.Ar word 1526inherits the type of quoting 1527(unquoted, double-quoted or here-document) 1528from the surroundings, 1529with the exception that a backslash that quotes a closing brace is removed 1530during quote removal. 1531.Bl -tag -width indent 1532.It Li ${# Ns Ar parameter Ns Li } 1533String Length. 1534The length in characters of 1535the value of 1536.Ar parameter . 1537.El 1538.Pp 1539The following four varieties of parameter expansion provide for substring 1540processing. 1541In each case, pattern matching notation 1542(see 1543.Sx Shell Patterns ) , 1544rather than regular expression notation, 1545is used to evaluate the patterns. 1546If parameter is one of the special parameters 1547.Va * 1548or 1549.Va @ , 1550the result of the expansion is unspecified. 1551Enclosing the full parameter expansion string in double-quotes does not 1552cause the following four varieties of pattern characters to be quoted, 1553whereas quoting characters within the braces has this effect. 1554.Bl -tag -width indent 1555.It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li } 1556Remove Smallest Suffix Pattern. 1557The 1558.Ar word 1559is expanded to produce a pattern. 1560The 1561parameter expansion then results in 1562.Ar parameter , 1563with the smallest portion of the 1564suffix matched by the pattern deleted. 1565.It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li } 1566Remove Largest Suffix Pattern. 1567The 1568.Ar word 1569is expanded to produce a pattern. 1570The 1571parameter expansion then results in 1572.Ar parameter , 1573with the largest portion of the 1574suffix matched by the pattern deleted. 1575.It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li } 1576Remove Smallest Prefix Pattern. 1577The 1578.Ar word 1579is expanded to produce a pattern. 1580The 1581parameter expansion then results in 1582.Ar parameter , 1583with the smallest portion of the 1584prefix matched by the pattern deleted. 1585.It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li } 1586Remove Largest Prefix Pattern. 1587The 1588.Ar word 1589is expanded to produce a pattern. 1590The 1591parameter expansion then results in 1592.Ar parameter , 1593with the largest portion of the 1594prefix matched by the pattern deleted. 1595.El 1596.Ss Command Substitution 1597Command substitution allows the output of a command to be substituted in 1598place of the command name itself. 1599Command substitution occurs when 1600the command is enclosed as follows: 1601.Pp 1602.D1 Li $( Ns Ar command Ns Li )\& 1603.Pp 1604or the backquoted version: 1605.Pp 1606.D1 Li ` Ns Ar command Ns Li ` 1607.Pp 1608The shell expands the command substitution by executing command 1609and replacing the command substitution 1610with the standard output of the command, 1611removing sequences of one or more newlines at the end of the substitution. 1612Embedded newlines before the end of the output are not removed; 1613however, during field splitting, they may be translated into spaces 1614depending on the value of 1615.Va IFS 1616and the quoting that is in effect. 1617The command is executed in a subshell environment, 1618except that the built-in commands 1619.Ic jobid , 1620.Ic jobs , 1621and 1622.Ic trap 1623return information about the parent shell environment 1624and 1625.Ic times 1626returns information about the same process 1627if they are the only command in a command substitution. 1628.Ss Arithmetic Expansion 1629Arithmetic expansion provides a mechanism for evaluating an arithmetic 1630expression and substituting its value. 1631The format for arithmetic expansion is as follows: 1632.Pp 1633.D1 Li $(( Ns Ar expression Ns Li )) 1634.Pp 1635The 1636.Ar expression 1637is treated as if it were in double-quotes, except 1638that a double-quote inside the expression is not treated specially. 1639The 1640shell expands all tokens in the 1641.Ar expression 1642for parameter expansion, 1643command substitution, 1644arithmetic expansion 1645and quote removal. 1646.Pp 1647The allowed expressions are a subset of C expressions, 1648summarized below. 1649.Bl -tag -width "Variables" -offset indent 1650.It Values 1651All values are of type 1652.Ft intmax_t . 1653.It Constants 1654Decimal, octal (starting with 1655.Li 0 ) 1656and hexadecimal (starting with 1657.Li 0x ) 1658integer constants. 1659.It Variables 1660Shell variables can be read and written 1661and contain integer constants. 1662.It Unary operators 1663.Li "! ~ + -" 1664.It Binary operators 1665.Li "* / % + - << >> < <= > >= == != & ^ | && ||" 1666.It Assignment operators 1667.Li "= += -= *= /= %= <<= >>= &= ^= |=" 1668.It Conditional operator 1669.Li "? :" 1670.El 1671.Pp 1672The result of the expression is substituted in decimal. 1673.Ss White Space Splitting (Field Splitting) 1674In certain contexts, 1675after parameter expansion, command substitution, and 1676arithmetic expansion the shell scans the results of 1677expansions and substitutions that did not occur in double-quotes for 1678field splitting and multiple fields can result. 1679.Pp 1680Characters in 1681.Va IFS 1682that are whitespace 1683.Po 1684.Aq space , 1685.Aq tab , 1686and 1687.Aq newline 1688.Pc 1689are treated differently from other characters in 1690.Va IFS . 1691.Pp 1692Whitespace in 1693.Va IFS 1694at the beginning or end of a word is discarded. 1695.Pp 1696Subsequently, a field is delimited by either 1697.Bl -enum 1698.It 1699a non-whitespace character in 1700.Va IFS 1701with any whitespace in 1702.Va IFS 1703surrounding it, or 1704.It 1705one or more whitespace characters in 1706.Va IFS . 1707.El 1708.Pp 1709If a word ends with a non-whitespace character in 1710.Va IFS , 1711there is no empty field after this character. 1712.Pp 1713If no field is delimited, the word is discarded. 1714In particular, if a word consists solely of an unquoted substitution 1715and the result of the substitution is null, 1716it is removed by field splitting even if 1717.Va IFS 1718is null. 1719.Ss Pathname Expansion (File Name Generation) 1720Unless the 1721.Fl f 1722option is set, 1723file name generation is performed 1724after word splitting is complete. 1725Each word is 1726viewed as a series of patterns, separated by slashes. 1727The 1728process of expansion replaces the word with the names of 1729all existing files whose names can be formed by replacing 1730each pattern with a string that matches the specified pattern. 1731There are two restrictions on this: first, a pattern cannot match 1732a string containing a slash, and second, 1733a pattern cannot match a string starting with a period 1734unless the first character of the pattern is a period. 1735The next section describes the patterns used for 1736Pathname Expansion, 1737the four varieties of parameter expansion for substring processing and the 1738.Ic case 1739command. 1740.Ss Shell Patterns 1741A pattern consists of normal characters, which match themselves, 1742and meta-characters. 1743The meta-characters are 1744.Ql * , 1745.Ql \&? , 1746and 1747.Ql \&[ . 1748These characters lose their special meanings if they are quoted. 1749When command or variable substitution is performed and the dollar sign 1750or back quotes are not double-quoted, the value of the 1751variable or the output of the command is scanned for these 1752characters and they are turned into meta-characters. 1753.Pp 1754An asterisk 1755.Pq Ql * 1756matches any string of characters. 1757A question mark 1758.Pq Ql \&? 1759matches any single character. 1760A left bracket 1761.Pq Ql \&[ 1762introduces a character class. 1763The end of the character class is indicated by a 1764.Ql \&] ; 1765if the 1766.Ql \&] 1767is missing then the 1768.Ql \&[ 1769matches a 1770.Ql \&[ 1771rather than introducing a character class. 1772A character class matches any of the characters between the square brackets. 1773A locale-dependent range of characters may be specified using a minus sign. 1774A named class of characters (see 1775.Xr wctype 3 ) 1776may be specified by surrounding the name with 1777.Ql \&[: 1778and 1779.Ql :\&] . 1780For example, 1781.Ql \&[\&[:alpha:\&]\&] 1782is a shell pattern that matches a single letter. 1783The character class may be complemented by making an exclamation point 1784.Pq Ql !\& 1785the first character of the character class. 1786A caret 1787.Pq Ql ^ 1788has the same effect but is non-standard. 1789.Pp 1790To include a 1791.Ql \&] 1792in a character class, make it the first character listed 1793(after the 1794.Ql \&! 1795or 1796.Ql ^ , 1797if any). 1798To include a 1799.Ql - , 1800make it the first or last character listed. 1801.Ss Built-in Commands 1802This section lists the built-in commands. 1803.Bl -tag -width indent 1804.It Ic \&: 1805A null command that returns a 0 (true) exit value. 1806.It Ic \&. Ar file 1807The commands in the specified file are read and executed by the shell. 1808The 1809.Ic return 1810command may be used to return to the 1811.Ic \&. 1812command's caller. 1813If 1814.Ar file 1815contains any 1816.Ql / 1817characters, it is used as is. 1818Otherwise, the shell searches the 1819.Va PATH 1820for the file. 1821If it is not found in the 1822.Va PATH , 1823it is sought in the current working directory. 1824.It Ic \&[ 1825A built-in equivalent of 1826.Xr test 1 . 1827.It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc Ar ... Oc 1828If 1829.Ar name Ns = Ns Ar string 1830is specified, the shell defines the alias 1831.Ar name 1832with value 1833.Ar string . 1834If just 1835.Ar name 1836is specified, the value of the alias 1837.Ar name 1838is printed. 1839With no arguments, the 1840.Ic alias 1841built-in command prints the names and values of all defined aliases 1842(see 1843.Ic unalias ) . 1844Alias values are written with appropriate quoting so that they are 1845suitable for re-input to the shell. 1846Also see the 1847.Sx Aliases 1848subsection. 1849.It Ic bg Op Ar job ... 1850Continue the specified jobs 1851(or the current job if no jobs are given) 1852in the background. 1853.It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc 1854List or alter key bindings for the line editor. 1855This command is documented in 1856.Xr editrc 5 . 1857.It Ic break Op Ar num 1858See the 1859.Sx Flow-Control Constructs 1860subsection. 1861.It Ic builtin Ar cmd Op Ar arg ... 1862Execute the specified built-in command, 1863.Ar cmd . 1864This is useful when the user wishes to override a shell function 1865with the same name as a built-in command. 1866.It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory 1867Switch to the specified 1868.Ar directory , 1869or to the directory specified in the 1870.Va HOME 1871environment variable if no 1872.Ar directory 1873is specified. 1874If 1875.Ar directory 1876does not begin with 1877.Pa / , \&. , 1878or 1879.Pa .. , 1880then the directories listed in the 1881.Va CDPATH 1882variable will be 1883searched for the specified 1884.Ar directory . 1885If 1886.Va CDPATH 1887is unset, the current directory is searched. 1888The format of 1889.Va CDPATH 1890is the same as that of 1891.Va PATH . 1892In an interactive shell, 1893the 1894.Ic cd 1895command will print out the name of the directory 1896that it actually switched to 1897if this is different from the name that the user gave. 1898These may be different either because the 1899.Va CDPATH 1900mechanism was used or because a symbolic link was crossed. 1901.Pp 1902If the 1903.Fl P 1904option is specified, 1905.Pa .. 1906is handled physically and symbolic links are resolved before 1907.Pa .. 1908components are processed. 1909If the 1910.Fl L 1911option is specified, 1912.Pa .. 1913is handled logically. 1914This is the default. 1915.Pp 1916The 1917.Fl e 1918option causes 1919.Ic cd 1920to return exit status 1 if the full pathname of the new directory 1921cannot be determined reliably or at all. 1922Normally this is not considered an error, 1923although a warning is printed. 1924.It Ic chdir 1925A synonym for the 1926.Ic cd 1927built-in command. 1928.It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ... 1929.It Ic command Oo Fl p Oc Fl v Ar utility 1930.It Ic command Oo Fl p Oc Fl V Ar utility 1931The first form of invocation executes the specified 1932.Ar utility , 1933ignoring shell functions in the search. 1934If 1935.Ar utility 1936is a special builtin, 1937it is executed as if it were a regular builtin. 1938.Pp 1939If the 1940.Fl p 1941option is specified, the command search is performed using a 1942default value of 1943.Va PATH 1944that is guaranteed to find all of the standard utilities. 1945.Pp 1946If the 1947.Fl v 1948option is specified, 1949.Ar utility 1950is not executed but a description of its interpretation by the shell is 1951printed. 1952For ordinary commands the output is the path name; for shell built-in 1953commands, shell functions and keywords only the name is written. 1954Aliases are printed as 1955.Dq Ic alias Ar name Ns = Ns Ar value . 1956.Pp 1957The 1958.Fl V 1959option is identical to 1960.Fl v 1961except for the output. 1962It prints 1963.Dq Ar utility Ic is Ar description 1964where 1965.Ar description 1966is either 1967the path name to 1968.Ar utility , 1969a special shell builtin, 1970a shell builtin, 1971a shell function, 1972a shell keyword 1973or 1974an alias for 1975.Ar value . 1976.It Ic continue Op Ar num 1977See the 1978.Sx Flow-Control Constructs 1979subsection. 1980.It Ic echo Oo Fl e | n Oc Op Ar string ... 1981Print a space-separated list of the arguments to the standard output 1982and append a newline character. 1983.Bl -tag -width indent 1984.It Fl n 1985Suppress the output of the trailing newline. 1986.It Fl e 1987Process C-style backslash escape sequences. 1988The 1989.Ic echo 1990command understands the following character escapes: 1991.Bl -tag -width indent 1992.It \ea 1993Alert (ring the terminal bell) 1994.It \eb 1995Backspace 1996.It \ec 1997Suppress the trailing newline (this has the side-effect of truncating the 1998line if it is not the last character) 1999.It \ee 2000The ESC character 2001.Tn ( ASCII 20020x1b) 2003.It \ef 2004Formfeed 2005.It \en 2006Newline 2007.It \er 2008Carriage return 2009.It \et 2010Horizontal tab 2011.It \ev 2012Vertical tab 2013.It \e\e 2014Literal backslash 2015.It \e0nnn 2016(Zero) The character whose octal value is 2017.Ar nnn 2018.El 2019.Pp 2020If 2021.Ar string 2022is not enclosed in quotes then the backslash itself must be escaped 2023with a backslash to protect it from the shell. 2024For example 2025.Bd -literal -offset indent 2026$ echo -e "a\evb" 2027a 2028 b 2029$ echo -e a\e\evb 2030a 2031 b 2032$ echo -e "a\e\eb" 2033a\eb 2034$ echo -e a\e\e\e\eb 2035a\eb 2036.Ed 2037.El 2038.Pp 2039Only one of the 2040.Fl e 2041and 2042.Fl n 2043options may be specified. 2044.It Ic eval Ar string ... 2045Concatenate all the arguments with spaces. 2046Then re-parse and execute the command. 2047.It Ic exec Op Ar command Op Ar arg ... 2048Unless 2049.Ar command 2050is omitted, 2051the shell process is replaced with the specified program 2052(which must be a real program, not a shell built-in command or function). 2053Any redirections on the 2054.Ic exec 2055command are marked as permanent, 2056so that they are not undone when the 2057.Ic exec 2058command finishes. 2059.It Ic exit Op Ar exitstatus 2060Terminate the shell process. 2061If 2062.Ar exitstatus 2063is given 2064it is used as the exit status of the shell. 2065Otherwise, if the shell is executing an 2066.Cm EXIT 2067trap, the exit status of the last command before the trap is used; 2068if the shell is executing a trap for a signal, 2069the shell exits by resending the signal to itself. 2070Otherwise, the exit status of the preceding command is used. 2071The exit status should be an integer between 0 and 255. 2072.It Ic export Ar name ... 2073.It Ic export Op Fl p 2074The specified names are exported so that they will 2075appear in the environment of subsequent commands. 2076The only way to un-export a variable is to 2077.Ic unset 2078it. 2079The shell allows the value of a variable to be set 2080at the same time as it is exported by writing 2081.Pp 2082.D1 Ic export Ar name Ns = Ns Ar value 2083.Pp 2084With no arguments the 2085.Ic export 2086command lists the names 2087of all exported variables. 2088If the 2089.Fl p 2090option is specified, the exported variables are printed as 2091.Dq Ic export Ar name Ns = Ns Ar value 2092lines, suitable for re-input to the shell. 2093.It Ic false 2094A null command that returns a non-zero (false) exit value. 2095.It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last 2096.It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last 2097.It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first 2098The 2099.Ic fc 2100built-in command lists, or edits and re-executes, 2101commands previously entered to an interactive shell. 2102.Bl -tag -width indent 2103.It Fl e Ar editor 2104Use the editor named by 2105.Ar editor 2106to edit the commands. 2107The 2108.Ar editor 2109string is a command name, 2110subject to search via the 2111.Va PATH 2112variable. 2113The value in the 2114.Va FCEDIT 2115variable is used as a default when 2116.Fl e 2117is not specified. 2118If 2119.Va FCEDIT 2120is null or unset, the value of the 2121.Va EDITOR 2122variable is used. 2123If 2124.Va EDITOR 2125is null or unset, 2126.Xr ed 1 2127is used as the editor. 2128.It Fl l No (ell) 2129List the commands rather than invoking 2130an editor on them. 2131The commands are written in the 2132sequence indicated by the 2133.Ar first 2134and 2135.Ar last 2136operands, as affected by 2137.Fl r , 2138with each command preceded by the command number. 2139.It Fl n 2140Suppress command numbers when listing with 2141.Fl l . 2142.It Fl r 2143Reverse the order of the commands listed 2144(with 2145.Fl l ) 2146or edited 2147(with neither 2148.Fl l 2149nor 2150.Fl s ) . 2151.It Fl s 2152Re-execute the command without invoking an editor. 2153.It Ar first 2154.It Ar last 2155Select the commands to list or edit. 2156The number of previous commands that can be accessed 2157are determined by the value of the 2158.Va HISTSIZE 2159variable. 2160The value of 2161.Ar first 2162or 2163.Ar last 2164or both are one of the following: 2165.Bl -tag -width indent 2166.It Oo Cm + Oc Ns Ar num 2167A positive number representing a command number; 2168command numbers can be displayed with the 2169.Fl l 2170option. 2171.It Fl Ar num 2172A negative decimal number representing the 2173command that was executed 2174.Ar num 2175of 2176commands previously. 2177For example, \-1 is the immediately previous command. 2178.It Ar string 2179A string indicating the most recently entered command 2180that begins with that string. 2181If the 2182.Ar old Ns = Ns Ar new 2183operand is not also specified with 2184.Fl s , 2185the string form of the first operand cannot contain an embedded equal sign. 2186.El 2187.El 2188.Pp 2189The following variables affect the execution of 2190.Ic fc : 2191.Bl -tag -width ".Va HISTSIZE" 2192.It Va FCEDIT 2193Name of the editor to use for history editing. 2194.It Va HISTSIZE 2195The number of previous commands that are accessible. 2196.El 2197.It Ic fg Op Ar job 2198Move the specified 2199.Ar job 2200or the current job to the foreground. 2201.It Ic getopts Ar optstring var 2202The 2203.Tn POSIX 2204.Ic getopts 2205command. 2206The 2207.Ic getopts 2208command deprecates the older 2209.Xr getopt 1 2210command. 2211The first argument should be a series of letters, each possibly 2212followed by a colon which indicates that the option takes an argument. 2213The specified variable is set to the parsed option. 2214The index of 2215the next argument is placed into the shell variable 2216.Va OPTIND . 2217If an option takes an argument, it is placed into the shell variable 2218.Va OPTARG . 2219If an invalid option is encountered, 2220.Ar var 2221is set to 2222.Ql \&? . 2223It returns a false value (1) when it encounters the end of the options. 2224.It Ic hash Oo Fl rv Oc Op Ar command ... 2225The shell maintains a hash table which remembers the locations of commands. 2226With no arguments whatsoever, the 2227.Ic hash 2228command prints out the contents of this table. 2229.Pp 2230With arguments, the 2231.Ic hash 2232command removes each specified 2233.Ar command 2234from the hash table (unless they are functions) and then locates it. 2235With the 2236.Fl v 2237option, 2238.Ic hash 2239prints the locations of the commands as it finds them. 2240The 2241.Fl r 2242option causes the 2243.Ic hash 2244command to delete all the entries in the hash table except for functions. 2245.It Ic jobid Op Ar job 2246Print the process IDs of the processes in the specified 2247.Ar job . 2248If the 2249.Ar job 2250argument is omitted, use the current job. 2251.It Ic jobs Oo Fl lps Oc Op Ar job ... 2252Print information about the specified jobs, or all jobs if no 2253.Ar job 2254argument is given. 2255The information printed includes job ID, status and command name. 2256.Pp 2257If the 2258.Fl l 2259option is specified, the PID of each job is also printed. 2260If the 2261.Fl p 2262option is specified, only the process IDs for the process group leaders 2263are printed, one per line. 2264If the 2265.Fl s 2266option is specified, only the PIDs of the job commands are printed, one per 2267line. 2268.It Ic kill 2269A built-in equivalent of 2270.Xr kill 1 2271that additionally supports sending signals to jobs. 2272.It Ic local Oo Ar variable ... Oc Op Fl 2273See the 2274.Sx Functions 2275subsection. 2276.It Ic printf 2277A built-in equivalent of 2278.Xr printf 1 . 2279.It Ic pwd Op Fl L | P 2280Print the path of the current directory. 2281The built-in command may 2282differ from the program of the same name because the 2283built-in command remembers what the current directory 2284is rather than recomputing it each time. 2285This makes 2286it faster. 2287However, if the current directory is 2288renamed, 2289the built-in version of 2290.Xr pwd 1 2291will continue to print the old name for the directory. 2292.Pp 2293If the 2294.Fl P 2295option is specified, symbolic links are resolved. 2296If the 2297.Fl L 2298option is specified, the shell's notion of the current directory 2299is printed (symbolic links are not resolved). 2300This is the default. 2301.It Ic read Oo Fl p Ar prompt Oc Oo 2302.Fl t Ar timeout Oc Oo Fl er Oc Ar variable ... 2303The 2304.Ar prompt 2305is printed if the 2306.Fl p 2307option is specified 2308and the standard input is a terminal. 2309Then a line is 2310read from the standard input. 2311The trailing newline 2312is deleted from the line and the line is split as 2313described in the section on 2314.Sx White Space Splitting (Field Splitting) 2315above, and 2316the pieces are assigned to the variables in order. 2317If there are more pieces than variables, the remaining 2318pieces (along with the characters in 2319.Va IFS 2320that separated them) 2321are assigned to the last variable. 2322If there are more variables than pieces, the remaining 2323variables are assigned the null string. 2324.Pp 2325Backslashes are treated specially, unless the 2326.Fl r 2327option is 2328specified. 2329If a backslash is followed by 2330a newline, the backslash and the newline will be 2331deleted. 2332If a backslash is followed by any other 2333character, the backslash will be deleted and the following 2334character will be treated as though it were not in 2335.Va IFS , 2336even if it is. 2337.Pp 2338If the 2339.Fl t 2340option is specified and the 2341.Ar timeout 2342elapses before a complete line of input is supplied, 2343the 2344.Ic read 2345command will return an exit status of 1 without assigning any values. 2346The 2347.Ar timeout 2348value may optionally be followed by one of 2349.Ql s , 2350.Ql m 2351or 2352.Ql h 2353to explicitly specify seconds, minutes or hours. 2354If none is supplied, 2355.Ql s 2356is assumed. 2357.Pp 2358The 2359.Fl e 2360option exists only for backward compatibility with older scripts. 2361.It Ic readonly Oo Fl p Oc Op Ar name ... 2362Each specified 2363.Ar name 2364is marked as read only, 2365so that it cannot be subsequently modified or unset. 2366The shell allows the value of a variable to be set 2367at the same time as it is marked read only 2368by using the following form: 2369.Pp 2370.D1 Ic readonly Ar name Ns = Ns Ar value 2371.Pp 2372With no arguments the 2373.Ic readonly 2374command lists the names of all read only variables. 2375If the 2376.Fl p 2377option is specified, the read-only variables are printed as 2378.Dq Ic readonly Ar name Ns = Ns Ar value 2379lines, suitable for re-input to the shell. 2380.It Ic return Op Ar exitstatus 2381See the 2382.Sx Functions 2383subsection. 2384.It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo 2385.Fl c Ar string Oc Op Fl - Ar arg ... 2386The 2387.Ic set 2388command performs three different functions: 2389.Bl -item 2390.It 2391With no arguments, it lists the values of all shell variables. 2392.It 2393If options are given, 2394either in short form or using the long 2395.Dq Fl /+o Ar longname 2396form, 2397it sets or clears the specified options as described in the section called 2398.Sx Argument List Processing . 2399.It 2400If the 2401.Dq Fl - 2402option is specified, 2403.Ic set 2404will replace the shell's positional parameters with the subsequent 2405arguments. 2406If no arguments follow the 2407.Dq Fl - 2408option, 2409all the positional parameters will be cleared, 2410which is equivalent to executing the command 2411.Dq Li "shift $#" . 2412The 2413.Dq Fl - 2414flag may be omitted when specifying arguments to be used 2415as positional replacement parameters. 2416This is not recommended, 2417because the first argument may begin with a dash 2418.Pq Ql - 2419or a plus 2420.Pq Ql + , 2421which the 2422.Ic set 2423command will interpret as a request to enable or disable options. 2424.El 2425.It Ic setvar Ar variable value 2426Assigns the specified 2427.Ar value 2428to the specified 2429.Ar variable . 2430The 2431.Ic setvar 2432command is intended to be used in functions that 2433assign values to variables whose names are passed as parameters. 2434In general it is better to write 2435.Dq Ar variable Ns = Ns Ar value 2436rather than using 2437.Ic setvar . 2438.It Ic shift Op Ar n 2439Shift the positional parameters 2440.Ar n 2441times, or once if 2442.Ar n 2443is not specified. 2444A shift sets the value of 2445.Li $1 2446to the value of 2447.Li $2 , 2448the value of 2449.Li $2 2450to the value of 2451.Li $3 , 2452and so on, 2453decreasing the value of 2454.Li $# 2455by one. 2456If there are zero positional parameters, shifting does not do anything. 2457.It Ic test 2458A built-in equivalent of 2459.Xr test 1 . 2460.It Ic times 2461Print the amount of time spent executing the shell process and its children. 2462The first output line shows the user and system times for the shell process 2463itself, the second one contains the user and system times for the 2464children. 2465.It Ic trap Oo Ar action Oc Ar signal ... 2466.It Ic trap Fl l 2467Cause the shell to parse and execute 2468.Ar action 2469when any specified 2470.Ar signal 2471is received. 2472The signals are specified by name or number. 2473In addition, the pseudo-signal 2474.Cm EXIT 2475may be used to specify an 2476.Ar action 2477that is performed when the shell terminates. 2478The 2479.Ar action 2480may be an empty string or a dash 2481.Pq Ql - ; 2482the former causes the specified signal to be ignored 2483and the latter causes the default action to be taken. 2484Omitting the 2485.Ar action 2486is another way to request the default action, for compatibility reasons this 2487usage is not recommended though. 2488In a subshell or utility environment, 2489the shell resets trapped (but not ignored) signals to the default action. 2490The 2491.Ic trap 2492command has no effect on signals that were ignored on entry to the shell. 2493.Pp 2494Option 2495.Fl l 2496causes the 2497.Ic trap 2498command to display a list of valid signal names. 2499.It Ic true 2500A null command that returns a 0 (true) exit value. 2501.It Ic type Op Ar name ... 2502Interpret each 2503.Ar name 2504as a command and print the resolution of the command search. 2505Possible resolutions are: 2506shell keyword, alias, special shell builtin, shell builtin, command, 2507tracked alias 2508and not found. 2509For aliases the alias expansion is printed; 2510for commands and tracked aliases 2511the complete pathname of the command is printed. 2512.It Ic ulimit Oo Fl HSabcdflmnstuv Oc Op Ar limit 2513Set or display resource limits (see 2514.Xr getrlimit 2 ) . 2515If 2516.Ar limit 2517is specified, the named resource will be set; 2518otherwise the current resource value will be displayed. 2519.Pp 2520If 2521.Fl H 2522is specified, the hard limits will be set or displayed. 2523While everybody is allowed to reduce a hard limit, 2524only the superuser can increase it. 2525The 2526.Fl S 2527option 2528specifies the soft limits instead. 2529When displaying limits, 2530only one of 2531.Fl S 2532or 2533.Fl H 2534can be given. 2535The default is to display the soft limits, 2536and to set both the hard and the soft limits. 2537.Pp 2538Option 2539.Fl a 2540causes the 2541.Ic ulimit 2542command to display all resources. 2543The parameter 2544.Ar limit 2545is not acceptable in this mode. 2546.Pp 2547The remaining options specify which resource value is to be 2548displayed or modified. 2549They are mutually exclusive. 2550.Bl -tag -width indent 2551.It Fl b Ar sbsize 2552The maximum size of socket buffer usage, in bytes. 2553.It Fl c Ar coredumpsize 2554The maximal size of core dump files, in 512-byte blocks. 2555.It Fl d Ar datasize 2556The maximal size of the data segment of a process, in kilobytes. 2557.It Fl f Ar filesize 2558The maximal size of a file, in 512-byte blocks. 2559.It Fl l Ar lockedmem 2560The maximal size of memory that can be locked by a process, in 2561kilobytes. 2562.It Fl m Ar memoryuse 2563The maximal resident set size of a process, in kilobytes. 2564.It Fl n Ar nofiles 2565The maximal number of descriptors that could be opened by a process. 2566.It Fl s Ar stacksize 2567The maximal size of the stack segment, in kilobytes. 2568.It Fl t Ar time 2569The maximal amount of CPU time to be used by each process, in seconds. 2570.It Fl u Ar userproc 2571The maximal number of simultaneous processes for this user ID. 2572.It Fl v Ar virtualmem 2573The maximal virtual size of a process, in kilobytes. 2574.El 2575.It Ic umask Oo Fl S Oc Op Ar mask 2576Set the file creation mask (see 2577.Xr umask 2 ) 2578to the octal or symbolic (see 2579.Xr chmod 1 ) 2580value specified by 2581.Ar mask . 2582If the argument is omitted, the current mask value is printed. 2583If the 2584.Fl S 2585option is specified, the output is symbolic, otherwise the output is octal. 2586.It Ic unalias Oo Fl a Oc Op Ar name ... 2587The specified alias names are removed. 2588If 2589.Fl a 2590is specified, all aliases are removed. 2591.It Ic unset Oo Fl fv Oc Ar name ... 2592The specified variables or functions are unset and unexported. 2593If the 2594.Fl v 2595option is specified or no options are given, the 2596.Ar name 2597arguments are treated as variable names. 2598If the 2599.Fl f 2600option is specified, the 2601.Ar name 2602arguments are treated as function names. 2603.It Ic wait Op Ar job 2604Wait for the specified 2605.Ar job 2606to complete and return the exit status of the last process in the 2607.Ar job . 2608If the argument is omitted, wait for all jobs to complete 2609and return an exit status of zero. 2610.El 2611.Ss Commandline Editing 2612When 2613.Nm 2614is being used interactively from a terminal, the current command 2615and the command history 2616(see 2617.Ic fc 2618in 2619.Sx Built-in Commands ) 2620can be edited using 2621.Nm vi Ns -mode 2622command line editing. 2623This mode uses commands similar 2624to a subset of those described in the 2625.Xr vi 1 2626man page. 2627The command 2628.Dq Li "set -o vi" 2629(or 2630.Dq Li "set -V" ) 2631enables 2632.Nm vi Ns -mode 2633editing and places 2634.Nm 2635into 2636.Nm vi 2637insert mode. 2638With 2639.Nm vi Ns -mode 2640enabled, 2641.Nm 2642can be switched between insert mode and command mode by typing 2643.Aq ESC . 2644Hitting 2645.Aq return 2646while in command mode will pass the line to the shell. 2647.Pp 2648Similarly, the 2649.Dq Li "set -o emacs" 2650(or 2651.Dq Li "set -E" ) 2652command can be used to enable a subset of 2653.Nm emacs Ns -style 2654command line editing features. 2655.Sh ENVIRONMENT 2656The following environment variables affect the execution of 2657.Nm : 2658.Bl -tag -width ".Ev LANGXXXXXX" 2659.It Ev ENV 2660Initialization file for interactive shells. 2661.It Ev LANG , Ev LC_* 2662Locale settings. 2663These are inherited by children of the shell, 2664and is used in a limited manner by the shell itself. 2665.It Ev PWD 2666An absolute pathname for the current directory, 2667possibly containing symbolic links. 2668This is used and updated by the shell. 2669.It Ev TERM 2670The default terminal setting for the shell. 2671This is inherited by children of the shell, and is used in the history 2672editing modes. 2673.El 2674.Pp 2675Additionally, all environment variables are turned into shell variables 2676at startup, 2677which may affect the shell as described under 2678.Sx Special Variables . 2679.Sh FILES 2680.Bl -tag -width "/etc/suid_profileXX" -compact 2681.It Pa ~/.profile 2682User's login profile. 2683.It Pa /etc/profile 2684System login profile. 2685.It Pa /etc/shells 2686Shell database. 2687.It Pa /etc/suid_profile 2688Privileged shell profile. 2689.El 2690.Sh EXIT STATUS 2691Errors that are detected by the shell, such as a syntax error, will 2692cause the shell to exit with a non-zero exit status. 2693If the shell is not an interactive shell, the execution of the shell 2694file will be aborted. 2695Otherwise the shell will return the exit status of the last command 2696executed, or if the 2697.Ic exit 2698builtin is used with a numeric argument, it 2699will return the argument. 2700.Sh SEE ALSO 2701.Xr builtin 1 , 2702.Xr chsh 1 , 2703.Xr echo 1 , 2704.Xr ed 1 , 2705.Xr emacs 1 Pq Pa editors/emacs , 2706.Xr kill 1 , 2707.Xr printf 1 , 2708.Xr pwd 1 , 2709.Xr test 1 , 2710.Xr vi 1 , 2711.Xr execve 2 , 2712.Xr getrlimit 2 , 2713.Xr umask 2 , 2714.Xr wctype 3 , 2715.Xr editrc 5 , 2716.Xr shells 5 , 2717.Xr script 7 2718.Sh HISTORY 2719A 2720.Nm 2721command, the Thompson shell, appeared in 2722.At v1 . 2723It was superseded in 2724.At v7 2725by the Bourne shell, which inherited the name 2726.Nm . 2727.Pp 2728This version of 2729.Nm 2730was rewritten in 1989 under the 2731.Bx 2732license after the Bourne shell from 2733.At V.4 . 2734.Sh AUTHORS 2735This version of 2736.Nm 2737was originally written by 2738.An Kenneth Almquist . 2739.Sh BUGS 2740The 2741.Nm 2742utility does not recognize multibyte characters other than UTF-8. 2743Splitting using 2744.Va IFS 2745and the line editing library 2746.Xr editline 3 2747do not recognize multibyte characters. 2748.Pp 2749The characters generated by filename completion should probably be quoted 2750to ensure that the filename is still valid after the input line has been 2751processed. 2752