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. All advertising materials mentioning features or use of this software 17.\" must display the following acknowledgement: 18.\" This product includes software developed by the University of 19.\" California, Berkeley and its contributors. 20.\" 4. Neither the name of the University nor the names of its contributors 21.\" may be used to endorse or promote products derived from this software 22.\" without specific prior written permission. 23.\" 24.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 25.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 26.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 27.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 28.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 29.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 30.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 31.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 32.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 33.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 34.\" SUCH DAMAGE. 35.\" 36.\" from: @(#)sh.1 8.6 (Berkeley) 5/4/95 37.\" $FreeBSD: src/bin/sh/sh.1,v 1.175 2011/11/05 21:56:45 jilles Exp $ 38.\" 39.Dd December 25, 2011 40.Dt SH 1 41.Os 42.Sh NAME 43.Nm sh 44.Nd command interpreter (shell) 45.Sh SYNOPSIS 46.Nm 47.Op Fl /+abCEefIimnPpTuVvx 48.Op Fl /+o Ar longname 49.Oo 50.Ar script 51.Op Ar arg ... 52.Oc 53.Nm 54.Op Fl /+abCEefIimnPpTuVvx 55.Op Fl /+o Ar longname 56.Fl c Ar string 57.Oo 58.Ar name 59.Op Ar arg ... 60.Oc 61.Nm 62.Op Fl /+abCEefIimnPpTuVvx 63.Op Fl /+o Ar longname 64.Fl s 65.Op Ar arg ... 66.Sh DESCRIPTION 67The 68.Nm 69utility is the standard command interpreter for the system. 70The current version of 71.Nm 72is close to the 73.St -p1003.1 74specification for the shell. 75It only supports features 76designated by 77.Tn POSIX , 78plus a few Berkeley extensions. 79This man page is not intended to be a tutorial nor a complete 80specification of the shell. 81.Ss Overview 82The shell is a command that reads lines from 83either a file or the terminal, interprets them, and 84generally executes other commands. 85It is the program that is started when a user logs into the system, 86although a user can select a different shell with the 87.Xr chsh 1 88command. 89The shell 90implements a language that has flow control constructs, 91a macro facility that provides a variety of features in 92addition to data storage, along with built-in history and line 93editing capabilities. 94It incorporates many features to 95aid interactive use and has the advantage that the interpretative 96language is common to both interactive and non-interactive 97use (shell scripts). 98That is, commands can be typed directly 99to the running shell or can be put into a file, 100which can be executed directly by the shell. 101.Ss Invocation 102.\" 103.\" XXX This next sentence is incredibly confusing. 104.\" 105If no arguments are present and if the standard input of the shell 106is connected to a terminal 107(or if the 108.Fl i 109option is set), 110the shell is considered an interactive shell. 111An interactive shell 112generally prompts before each command and handles programming 113and command errors differently (as described below). 114When first starting, the shell inspects argument 0, and 115if it begins with a dash 116.Pq Ql - , 117the shell is also considered a login shell. 118This is normally done automatically by the system 119when the user first logs in. 120A login shell first reads commands 121from the files 122.Pa /etc/profile 123and then 124.Pa .profile 125in a user's home directory, 126if they exist. 127If the environment variable 128.Ev ENV 129is set on entry to a shell, or is set in the 130.Pa .profile 131of a login shell, the shell then subjects its value to parameter expansion 132and arithmetic expansion and reads commands from the named file. 133Therefore, a user should place commands that are to be executed only 134at login time in the 135.Pa .profile 136file, and commands that are executed for every shell inside the 137.Ev ENV 138file. 139The user can set the 140.Ev ENV 141variable to some file by placing the following line in the file 142.Pa .profile 143in the home directory, 144substituting for 145.Pa .shinit 146the filename desired: 147.Pp 148.Dl "ENV=$HOME/.shinit; export ENV" 149.Pp 150The first non-option argument specified on the command line 151will be treated as the 152name of a file from which to read commands (a shell script), and 153the remaining arguments are set as the positional parameters 154of the shell 155.Li ( $1 , $2 , 156etc.). 157Otherwise, the shell reads commands 158from its standard input. 159.Pp 160Unlike older versions of 161.Nm 162the 163.Ev ENV 164script is only sourced on invocation of interactive shells. 165This 166closes a well-known, and sometimes easily exploitable security 167hole related to poorly thought out 168.Ev ENV 169scripts. 170.Ss Argument List Processing 171All of the single letter options to 172.Nm 173have a corresponding long name, 174with the exception of 175.Fl c 176and 177.Fl /+o . 178These long names are provided next to the single letter options 179in the descriptions below. 180The long name for an option may be specified as an argument to the 181.Fl /+o 182option of 183.Nm . 184Once the shell is running, 185the long name for an option may be specified as an argument to the 186.Fl /+o 187option of the 188.Ic set 189built-in command 190(described later in the section called 191.Sx Built-in Commands ) . 192Introducing an option with a dash 193.Pq Ql - 194enables the option, 195while using a plus 196.Pq Ql + 197disables the option. 198A 199.Dq Li -- 200or plain 201.Ql - 202will stop option processing and will force the remaining 203words on the command line to be treated as arguments. 204The 205.Fl /+o 206and 207.Fl c 208options do not have long names. 209They take arguments and are described after the single letter options. 210.Bl -tag -width indent 211.It Fl a Li allexport 212Flag variables for export when assignments are made to them. 213.It Fl b Li notify 214Enable asynchronous notification of background job 215completion. 216(UNIMPLEMENTED) 217.It Fl C Li noclobber 218Do not overwrite existing files with 219.Ql > . 220.It Fl E Li emacs 221Enable the built-in 222.Xr emacs 1 223command line editor (disables the 224.Fl V 225option if it has been set; 226set automatically when interactive on terminals). 227.It Fl e Li errexit 228Exit immediately if any untested command fails in non-interactive mode. 229The exit status of a command is considered to be 230explicitly tested if the command is part of the list used to control 231an 232.Ic if , elif , while , 233or 234.Ic until ; 235if the command is the left 236hand operand of an 237.Dq Li && 238or 239.Dq Li || 240operator; or if the command is a pipeline preceded by the 241.Ic !\& 242operator. 243If a shell function is executed and its exit status is explicitly 244tested, all commands of the function are considered to be tested as 245well. 246.It Fl f Li noglob 247Disable pathname expansion. 248.It Fl h Li trackall 249A do-nothing option for 250.Tn POSIX 251compliance. 252.It Fl I Li ignoreeof 253Ignore 254.Dv EOF Ap s 255from input when in interactive mode. 256.It Fl i Li interactive 257Force the shell to behave interactively. 258.It Fl m Li monitor 259Turn on job control (set automatically when interactive). 260.It Fl n Li noexec 261If not interactive, read commands but do not 262execute them. 263This is useful for checking the 264syntax of shell scripts. 265.It Fl P Li physical 266Change the default for the 267.Ic cd 268and 269.Ic pwd 270commands from 271.Fl L 272(logical directory layout) 273to 274.Fl P 275(physical directory layout). 276.It Fl p Li privileged 277Turn on privileged mode. 278This mode is enabled on startup 279if either the effective user or group ID is not equal to the 280real user or group ID. 281Turning this mode off sets the 282effective user and group IDs to the real user and group IDs. 283When this mode is enabled for interactive shells, the file 284.Pa /etc/suid_profile 285is sourced instead of 286.Pa ~/.profile 287after 288.Pa /etc/profile 289is sourced, and the contents of the 290.Ev ENV 291variable are ignored. 292.It Fl s Li stdin 293Read commands from standard input (set automatically 294if no file arguments are present). 295This option has 296no effect when set after the shell has already started 297running (i.e., when set with the 298.Ic set 299command). 300.It Fl T Li trapsasync 301When waiting for a child, execute traps immediately. 302If this option is not set, 303traps are executed after the child exits, 304as specified in 305.St -p1003.2 . 306This nonstandard option is useful for putting guarding shells around 307children that block signals. 308The surrounding shell may kill the child 309or it may just return control to the tty and leave the child alone, 310like this: 311.Bd -literal -offset indent 312sh -T -c "trap 'exit 1' 2 ; some-blocking-program" 313.Ed 314.It Fl u Li nounset 315Write a message to standard error when attempting 316to expand a variable, a positional parameter or 317the special parameter 318.Va \&! 319that is not set, and if the 320shell is not interactive, exit immediately. 321.It Fl V Li vi 322Enable the built-in 323.Xr vi 1 324command line editor (disables 325.Fl E 326if it has been set). 327.It Fl v Li verbose 328The shell writes its input to standard error 329as it is read. 330Useful for debugging. 331.It Fl x Li xtrace 332Write each command 333(preceded by the value of the 334.Va PS4 335variable subjected to parameter expansion and arithmetic expansion) 336to standard error before it is executed. 337Useful for debugging. 338.It "\ \ " Em tabcomplete 339Enables filename completion in the command line editor. 340Typing a tab character will extend the current input word to match a 341filename. 342If more than one filename matches it is only extended to be the common prefix. 343Typing a second tab character will list all the matching names. 344Turned on by default in an interactive shell. 345.El 346.Pp 347The 348.Fl c 349option causes the commands to be read from the 350.Ar string 351operand instead of from the standard input. 352Keep in mind that this option only accepts a single string as its 353argument, hence multi-word strings must be quoted. 354.Pp 355The 356.Fl /+o 357option takes as its only argument the long name of an option 358to be enabled or disabled. 359For example, the following two invocations of 360.Nm 361both enable the built-in 362.Xr emacs 1 363command line editor: 364.Bd -literal -offset indent 365set -E 366set -o emacs 367.Ed 368.Pp 369If used without an argument, the 370.Fl o 371option displays the current option settings in a human-readable format. 372If 373.Cm +o 374is used without an argument, the current option settings are output 375in a format suitable for re-input into the shell. 376.Ss Lexical Structure 377The shell reads input in terms of lines from a file and breaks 378it up into words at whitespace (blanks and tabs), and at 379certain sequences of 380characters called 381.Dq operators , 382which are special to the shell. 383There are two types of operators: control operators and 384redirection operators (their meaning is discussed later). 385The following is a list of valid operators: 386.Bl -tag -width indent 387.It Control operators: 388.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 389.It Li & Ta Li && Ta Li ( Ta Li ) Ta Li \en 390.It Li ;; Ta Li ;& Ta Li ; Ta Li | Ta Li || 391.El 392.It Redirection operators: 393.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 394.It Li < Ta Li > Ta Li << Ta Li >> Ta Li <> 395.It Li <& Ta Li >& Ta Li <<- Ta Li >| 396.El 397.El 398.Pp 399The character 400.Ql # 401introduces a comment if used at the beginning of a word. 402The word starting with 403.Ql # 404and the rest of the line are ignored. 405.Pp 406.Tn ASCII 407.Dv NUL 408characters (character code 0) are not allowed in shell input. 409.Ss Quoting 410Quoting is used to remove the special meaning of certain characters 411or words to the shell, such as operators, whitespace, keywords, 412or alias names. 413.Pp 414There are four types of quoting: matched single quotes, 415dollar-single quotes, 416matched double quotes, and backslash. 417.Bl -tag -width indent 418.It Single Quotes 419Enclosing characters in single quotes preserves the literal 420meaning of all the characters (except single quotes, making 421it impossible to put single-quotes in a single-quoted string). 422.It Dollar-Single Quotes 423Enclosing characters between 424.Li $' 425and 426.Li ' 427preserves the literal meaning of all characters 428except backslashes and single quotes. 429A backslash introduces a C-style escape sequence: 430.Bl -tag -width xUnnnnnnnn 431.It \ea 432Alert (ring the terminal bell) 433.It \eb 434Backspace 435.It \ec Ns Ar c 436The control character denoted by 437.Li ^ Ns Ar c 438in 439.Xr stty 1 . 440If 441.Ar c 442is a backslash, it must be doubled. 443.It \ee 444The ESC character 445.Tn ( ASCII 4460x1b) 447.It \ef 448Formfeed 449.It \en 450Newline 451.It \er 452Carriage return 453.It \et 454Horizontal tab 455.It \ev 456Vertical tab 457.It \e\e 458Literal backslash 459.It \e\&' 460Literal single-quote 461.It \e\&" 462Literal double-quote 463.It \e Ns Ar nnn 464The byte whose octal value is 465.Ar nnn 466(one to three digits) 467.It \ex Ns Ar nn 468The byte whose hexadecimal value is 469.Ar nn 470(one or more digits only the last two of which are used) 471.It \eu Ns Ar nnnn 472The Unicode code point 473.Ar nnnn 474(four hexadecimal digits) 475.It \eU Ns Ar nnnnnnnn 476The Unicode code point 477.Ar nnnnnnnn 478(eight hexadecimal digits) 479.El 480.Pp 481The sequences for Unicode code points are currently only useful with 482UTF-8 locales. 483They reject code point 0 and UTF-16 surrogates. 484.Pp 485If an escape sequence would produce a byte with value 0, 486that byte and the rest of the string until the matching single-quote 487are ignored. 488.Pp 489Any other string starting with a backslash is an error. 490.It Double Quotes 491Enclosing characters within double quotes preserves the literal 492meaning of all characters except dollar sign 493.Pq Ql $ , 494backquote 495.Pq Ql ` , 496and backslash 497.Pq Ql \e . 498The backslash inside double quotes is historically weird. 499It remains literal unless it precedes the following characters, 500which it serves to quote: 501.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 502.It Li $ Ta Li ` Ta Li \&" Ta Li \e\ Ta Li \en 503.El 504.It Backslash 505A backslash preserves the literal meaning of the following 506character, with the exception of the newline character 507.Pq Ql \en . 508A backslash preceding a newline is treated as a line continuation. 509.El 510.Ss Keywords 511Keywords or reserved words are words that have special meaning to the 512shell and are recognized at the beginning of a line and 513after a control operator. 514The following are keywords: 515.Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center 516.It Li \&! Ta { Ta } Ta Ic case Ta Ic do 517.It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi 518.It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while 519.El 520.Ss Aliases 521An alias is a name and corresponding value set using the 522.Ic alias 523built-in command. 524Wherever the command word of a simple command may occur, 525and after checking for keywords if a keyword may occur, the shell 526checks the word to see if it matches an alias. 527If it does, it replaces it in the input stream with its value. 528For example, if there is an alias called 529.Dq Li lf 530with the value 531.Dq Li "ls -F" , 532then the input 533.Pp 534.Dl "lf foobar" 535.Pp 536would become 537.Pp 538.Dl "ls -F foobar" 539.Pp 540Aliases provide a convenient way for naive users to 541create shorthands for commands without having to learn how 542to create functions with arguments. 543Using aliases in scripts is discouraged 544because the command that defines them must be executed 545before the code that uses them is parsed. 546This is fragile and not portable. 547.Pp 548An alias name may be escaped in a command line, so that it is not 549replaced by its alias value, by using quoting characters within or 550adjacent to the alias name. 551This is most often done by prefixing 552an alias name with a backslash to execute a function, built-in, or 553normal program with the same name. 554See the 555.Sx Quoting 556subsection. 557.Ss Commands 558The shell interprets the words it reads according to a 559language, the specification of which is outside the scope 560of this man page (refer to the BNF in the 561.St -p1003.2 562document). 563Essentially though, a line is read and if 564the first word of the line (or after a control operator) 565is not a keyword, then the shell has recognized a 566simple command. 567Otherwise, a complex command or some 568other special construct may have been recognized. 569.Ss Simple Commands 570If a simple command has been recognized, the shell performs 571the following actions: 572.Bl -enum 573.It 574Leading words of the form 575.Dq Li name=value 576are stripped off and assigned to the environment of 577the simple command. 578Redirection operators and 579their arguments (as described below) are stripped 580off and saved for processing. 581.It 582The remaining words are expanded as described in 583the section called 584.Sx Word Expansions , 585and the first remaining word is considered the command 586name and the command is located. 587The remaining 588words are considered the arguments of the command. 589If no command name resulted, then the 590.Dq Li name=value 591variable assignments recognized in 1) affect the 592current shell. 593.It 594Redirections are performed as described in 595the next section. 596.El 597.Ss Redirections 598Redirections are used to change where a command reads its input 599or sends its output. 600In general, redirections open, close, or 601duplicate an existing reference to a file. 602The overall format 603used for redirection is: 604.Pp 605.D1 Oo Ar n Oc Ar redir-op file 606.Pp 607The 608.Ar redir-op 609is one of the redirection operators mentioned 610previously. 611The following gives some examples of how these 612operators can be used. 613Note that stdin and stdout are commonly used abbreviations 614for standard input and standard output respectively. 615.Bl -tag -width "1234567890XX" -offset indent 616.It Oo Ar n Oc Ns Li > Ar file 617redirect stdout (or file descriptor 618.Ar n ) 619to 620.Ar file 621.It Oo Ar n Oc Ns Li >| Ar file 622same as above, but override the 623.Fl C 624option 625.It Oo Ar n Oc Ns Li >> Ar file 626append stdout (or file descriptor 627.Ar n ) 628to 629.Ar file 630.It Oo Ar n Oc Ns Li < Ar file 631redirect stdin (or file descriptor 632.Ar n ) 633from 634.Ar file 635.It Oo Ar n Oc Ns Li <> Ar file 636redirect stdin (or file descriptor 637.Ar n ) 638to and from 639.Ar file 640.It Oo Ar n1 Oc Ns Li <& Ns Ar n2 641duplicate stdin (or file descriptor 642.Ar n1 ) 643from file descriptor 644.Ar n2 645.It Oo Ar n Oc Ns Li <&- 646close stdin (or file descriptor 647.Ar n ) 648.It Oo Ar n1 Oc Ns Li >& Ns Ar n2 649duplicate stdout (or file descriptor 650.Ar n1 ) 651to file descriptor 652.Ar n2 653.It Oo Ar n Oc Ns Li >&- 654close stdout (or file descriptor 655.Ar n ) 656.El 657.Pp 658The following redirection is often called a 659.Dq here-document . 660.Bd -unfilled -offset indent 661.Oo Ar n Oc Ns Li << Ar delimiter 662.D1 Ar here-doc-text 663.D1 ... 664.Ar delimiter 665.Ed 666.Pp 667All the text on successive lines up to the delimiter is 668saved away and made available to the command on standard 669input, or file descriptor 670.Ar n 671if it is specified. 672If the 673.Ar delimiter 674as specified on the initial line is quoted, then the 675.Ar here-doc-text 676is treated literally, otherwise the text is subjected to 677parameter expansion, command substitution, and arithmetic 678expansion (as described in the section on 679.Sx Word Expansions ) . 680If the operator is 681.Dq Li <<- 682instead of 683.Dq Li << , 684then leading tabs 685in the 686.Ar here-doc-text 687are stripped. 688.Ss Search and Execution 689There are three types of commands: shell functions, 690built-in commands, and normal programs. 691The command is searched for (by name) in that order. 692The three types of commands are all executed in a different way. 693.Pp 694When a shell function is executed, all of the shell positional 695parameters (except 696.Li $0 , 697which remains unchanged) are 698set to the arguments of the shell function. 699The variables which are explicitly placed in the environment of 700the command (by placing assignments to them before the 701function name) are made local to the function and are set 702to the values given. 703Then the command given in the function definition is executed. 704The positional parameters are restored to their original values 705when the command completes. 706This all occurs within the current shell. 707.Pp 708Shell built-in commands are executed internally to the shell, without 709spawning a new process. 710There are two kinds of built-in commands: regular and special. 711Assignments before special builtins persist after they finish 712executing and assignment errors, redirection errors and certain 713operand errors cause a script to be aborted. 714Special builtins cannot be overridden with a function. 715Both regular and special builtins can affect the shell in ways 716normal programs cannot. 717.Pp 718Otherwise, if the command name does not match a function 719or built-in command, the command is searched for as a normal 720program in the file system (as described in the next section). 721When a normal program is executed, the shell runs the program, 722passing the arguments and the environment to the program. 723If the program is not a normal executable file 724(i.e., if it does not begin with the 725.Dq "magic number" 726whose 727.Tn ASCII 728representation is 729.Dq Li #! , 730resulting in an 731.Er ENOEXEC 732return value from 733.Xr execve 2 ) 734but appears to be a text file, 735the shell will run a new instance of 736.Nm 737to interpret it. 738.Pp 739Note that previous versions of this document 740and the source code itself misleadingly and sporadically 741refer to a shell script without a magic number 742as a 743.Dq "shell procedure" . 744.Ss Path Search 745When locating a command, the shell first looks to see if 746it has a shell function by that name. 747Then it looks for a 748built-in command by that name. 749If a built-in command is not found, 750one of two things happen: 751.Bl -enum 752.It 753Command names containing a slash are simply executed without 754performing any searches. 755.It 756The shell searches each entry in the 757.Va PATH 758variable 759in turn for the command. 760The value of the 761.Va PATH 762variable should be a series of 763entries separated by colons. 764Each entry consists of a 765directory name. 766The current directory 767may be indicated implicitly by an empty directory name, 768or explicitly by a single period. 769.El 770.Ss Command Exit Status 771Each command has an exit status that can influence the behavior 772of other shell commands. 773The paradigm is that a command exits 774with zero for normal or success, and non-zero for failure, 775error, or a false indication. 776The man page for each command 777should indicate the various exit codes and what they mean. 778Additionally, the built-in commands return exit codes, as does 779an executed shell function. 780.Pp 781If a command is terminated by a signal, its exit status is 128 plus 782the signal number. 783Signal numbers are defined in the header file 784.In sys/signal.h . 785.Ss Complex Commands 786Complex commands are combinations of simple commands 787with control operators or keywords, together creating a larger complex 788command. 789More generally, a command is one of the following: 790.Bl -item -offset indent 791.It 792simple command 793.It 794pipeline 795.It 796list or compound-list 797.It 798compound command 799.It 800function definition 801.El 802.Pp 803Unless otherwise stated, the exit status of a command is 804that of the last simple command executed by the command. 805.Ss Pipelines 806A pipeline is a sequence of one or more commands separated 807by the control operator 808.Ql \&| . 809The standard output of all but 810the last command is connected to the standard input 811of the next command. 812The standard output of the last 813command is inherited from the shell, as usual. 814.Pp 815The format for a pipeline is: 816.Pp 817.D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ... 818.Pp 819The standard output of 820.Ar command1 821is connected to the standard input of 822.Ar command2 . 823The standard input, standard output, or 824both of a command is considered to be assigned by the 825pipeline before any redirection specified by redirection 826operators that are part of the command. 827.Pp 828Note that unlike some other shells, 829.Nm 830executes each process in a pipeline with more than one command 831in a subshell environment and as a child of the 832.Nm 833process. 834.Pp 835If the pipeline is not in the background (discussed later), 836the shell waits for all commands to complete. 837.Pp 838If the keyword 839.Ic !\& 840does not precede the pipeline, the 841exit status is the exit status of the last command specified 842in the pipeline. 843Otherwise, the exit status is the logical 844NOT of the exit status of the last command. 845That is, if 846the last command returns zero, the exit status is 1; if 847the last command returns greater than zero, the exit status 848is zero. 849.Pp 850Because pipeline assignment of standard input or standard 851output or both takes place before redirection, it can be 852modified by redirection. 853For example: 854.Pp 855.Dl "command1 2>&1 | command2" 856.Pp 857sends both the standard output and standard error of 858.Ar command1 859to the standard input of 860.Ar command2 . 861.Pp 862A 863.Ql \&; 864or newline terminator causes the preceding 865AND-OR-list 866(described below in the section called 867.Sx Short-Circuit List Operators ) 868to be executed sequentially; 869an 870.Ql & 871causes asynchronous execution of the preceding AND-OR-list. 872.Ss Background Commands (&) 873If a command is terminated by the control operator ampersand 874.Pq Ql & , 875the shell executes the command in a subshell environment (see 876.Sx Grouping Commands Together 877below) and asynchronously; 878the shell does not wait for the command to finish 879before executing the next command. 880.Pp 881The format for running a command in background is: 882.Pp 883.D1 Ar command1 Li & Op Ar command2 Li & Ar ... 884.Pp 885If the shell is not interactive, the standard input of an 886asynchronous command is set to 887.Pa /dev/null . 888.Ss Lists (Generally Speaking) 889A list is a sequence of zero or more commands separated by 890newlines, semicolons, or ampersands, 891and optionally terminated by one of these three characters. 892The commands in a 893list are executed in the order they are written. 894If command is followed by an ampersand, the shell starts the 895command and immediately proceeds onto the next command; 896otherwise it waits for the command to terminate before 897proceeding to the next one. 898.Ss Short-Circuit List Operators 899.Dq Li && 900and 901.Dq Li || 902are AND-OR list operators. 903.Dq Li && 904executes the first command, and then executes the second command 905if the exit status of the first command is zero. 906.Dq Li || 907is similar, but executes the second command if the exit 908status of the first command is nonzero. 909.Dq Li && 910and 911.Dq Li || 912both have the same priority. 913.Ss Flow-Control Constructs (if, while, for, case) 914The syntax of the 915.Ic if 916command is: 917.Bd -unfilled -offset indent -compact 918.Ic if Ar list 919.Ic then Ar list 920.Oo Ic elif Ar list 921.Ic then Ar list Oc Ar ... 922.Op Ic else Ar list 923.Ic fi 924.Ed 925.Pp 926The syntax of the 927.Ic while 928command is: 929.Bd -unfilled -offset indent -compact 930.Ic while Ar list 931.Ic do Ar list 932.Ic done 933.Ed 934.Pp 935The two lists are executed repeatedly while the exit status of the 936first list is zero. 937The 938.Ic until 939command is similar, but has the word 940.Ic until 941in place of 942.Ic while , 943which causes it to 944repeat until the exit status of the first list is zero. 945.Pp 946The syntax of the 947.Ic for 948command is: 949.Bd -unfilled -offset indent -compact 950.Ic for Ar variable Op Ic in Ar word ... 951.Ic do Ar list 952.Ic done 953.Ed 954.Pp 955If 956.Ic in 957and the following words are omitted, 958.Ic in Li \&"$@\&" 959is used instead. 960The words are expanded, and then the list is executed 961repeatedly with the variable set to each word in turn. 962The 963.Ic do 964and 965.Ic done 966commands may be replaced with 967.Ql { 968and 969.Ql } . 970.Pp 971The syntax of the 972.Ic break 973and 974.Ic continue 975commands is: 976.D1 Ic break Op Ar num 977.D1 Ic continue Op Ar num 978.Pp 979The 980.Ic break 981command terminates the 982.Ar num 983innermost 984.Ic for 985or 986.Ic while 987loops. 988The 989.Ic continue 990command continues with the next iteration of the innermost loop. 991These are implemented as special built-in commands. 992.Pp 993The syntax of the 994.Ic case 995command is: 996.Bd -unfilled -offset indent -compact 997.Ic case Ar word Ic in 998.Ar pattern Ns Li ) Ar list Li ;; 999.Ar ... 1000.Ic esac 1001.Ed 1002.Pp 1003The pattern can actually be one or more patterns 1004(see 1005.Sx Shell Patterns 1006described later), 1007separated by 1008.Ql \&| 1009characters. 1010Tilde expansion, parameter expansion, command substitution, 1011arithmetic expansion and quote removal are applied to the word. 1012Then, each pattern is expanded in turn using tilde expansion, 1013parameter expansion, command substitution and arithmetic expansion and 1014the expanded form of the word is checked against it. 1015If a match is found, the corresponding list is executed. 1016If the selected list is terminated by the control operator 1017.Ql ;& 1018instead of 1019.Ql ;; , 1020execution continues with the next list, 1021continuing until a list terminated with 1022.Ql ;; 1023or the end of the 1024.Ic case 1025command. 1026The exit code of the 1027.Ic case 1028command is the exit code of the last command executed in the list or 1029zero if no patterns were matched. 1030.Ss Grouping Commands Together 1031Commands may be grouped by writing either 1032.Pp 1033.D1 Li \&( Ns Ar list Ns Li \%) 1034.Pp 1035or 1036.Pp 1037.D1 Li { Ar list Ns Li \&; } 1038.Pp 1039The first form executes the commands in a subshell environment. 1040A subshell environment has its own copy of: 1041.Bl -enum 1042.It 1043The current working directory as set by 1044.Ic cd . 1045.It 1046The file creation mask as set by 1047.Ic umask . 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 1074The second form never forks another shell, 1075so it is slightly more efficient. 1076Grouping commands together this way allows the user to 1077redirect their output as though they were one program: 1078.Bd -literal -offset indent 1079{ echo -n "hello"; echo " world"; } > greeting 1080.Ed 1081.Ss Functions 1082The syntax of a function definition is 1083.Pp 1084.D1 Ar name Li \&( \&) Ar command 1085.Pp 1086A function definition is an executable statement; when 1087executed it installs a function named 1088.Ar name 1089and returns an 1090exit status of zero. 1091The 1092.Ar command 1093is normally a list 1094enclosed between 1095.Ql { 1096and 1097.Ql } . 1098.Pp 1099Variables may be declared to be local to a function by 1100using the 1101.Ic local 1102command. 1103This should appear as the first statement of a function, 1104and the syntax is: 1105.Pp 1106.D1 Ic local Oo Ar variable ... Oc Op Fl 1107.Pp 1108The 1109.Ic local 1110command is implemented as a built-in command. 1111.Pp 1112When a variable is made local, it inherits the initial 1113value and exported and readonly flags from the variable 1114with the same name in the surrounding scope, if there is 1115one. 1116Otherwise, the variable is initially unset. 1117The shell 1118uses dynamic scoping, so that if the variable 1119.Va x 1120is made local to function 1121.Em f , 1122which then calls function 1123.Em g , 1124references to the variable 1125.Va x 1126made inside 1127.Em g 1128will refer to the variable 1129.Va x 1130declared inside 1131.Em f , 1132not to the global variable named 1133.Va x . 1134.Pp 1135The only special parameter that can be made local is 1136.Ql - . 1137Making 1138.Ql - 1139local causes any shell options that are 1140changed via the 1141.Ic set 1142command inside the function to be 1143restored to their original values when the function 1144returns. 1145.Pp 1146The syntax of the 1147.Ic return 1148command is 1149.Pp 1150.D1 Ic return Op Ar exitstatus 1151.Pp 1152It terminates the current executional scope, returning from the previous 1153nested function, sourced script, or shell instance, in that order. 1154The 1155.Ic return 1156command is implemented as a special built-in command. 1157.Ss Variables and Parameters 1158The shell maintains a set of parameters. 1159A parameter 1160denoted by a name is called a variable. 1161When starting up, 1162the shell turns all the environment variables into shell 1163variables. 1164New variables can be set using the form 1165.Pp 1166.D1 Ar name Ns = Ns Ar value 1167.Pp 1168Variables set by the user must have a name consisting solely 1169of alphabetics, numerics, and underscores. 1170The first letter of a variable name must not be numeric. 1171A parameter can also be denoted by a number 1172or a special character as explained below. 1173.Pp 1174Assignments are expanded differently from other words: 1175tilde expansion is also performed after the equals sign and after any colon 1176and usernames are also terminated by colons, 1177and field splitting and pathname expansion are not performed. 1178.Ss Positional Parameters 1179A positional parameter is a parameter denoted by a number greater than zero. 1180The shell sets these initially to the values of its command line 1181arguments that follow the name of the shell script. 1182The 1183.Ic set 1184built-in command can also be used to set or reset them. 1185.Ss Special Parameters 1186Special parameters are parameters denoted by a single special character 1187or the digit zero. 1188They are shown in the following list, exactly as they would appear in input 1189typed by the user or in the source of a shell script. 1190.Bl -hang 1191.It Li $* 1192Expands to the positional parameters, starting from one. 1193When 1194the expansion occurs within a double-quoted string 1195it expands to a single field with the value of each parameter 1196separated by the first character of the 1197.Va IFS 1198variable, 1199or by a space if 1200.Va IFS 1201is unset. 1202.It Li $@ 1203Expands to the positional parameters, starting from one. 1204When 1205the expansion occurs within double-quotes, each positional 1206parameter expands as a separate argument. 1207If there are no positional parameters, the 1208expansion of 1209.Li @ 1210generates zero arguments, even when 1211.Li @ 1212is double-quoted. 1213What this basically means, for example, is 1214if 1215.Li $1 1216is 1217.Dq Li abc 1218and 1219.Li $2 1220is 1221.Dq Li "def ghi" , 1222then 1223.Li \&"$@\&" 1224expands to 1225the two arguments: 1226.Bd -literal -offset indent 1227"abc" "def ghi" 1228.Ed 1229.It Li $# 1230Expands to the number of positional parameters. 1231.It Li $? 1232Expands to the exit status of the most recent pipeline. 1233.It Li $- 1234(hyphen) Expands to the current option flags (the single-letter 1235option names concatenated into a string) as specified on 1236invocation, by the 1237.Ic set 1238built-in command, or implicitly 1239by the shell. 1240.It Li $$ 1241Expands to the process ID of the invoked shell. 1242A subshell 1243retains the same value of 1244.Va $ 1245as its parent. 1246.It Li $! 1247Expands to the process ID of the most recent background 1248command executed from the current shell. 1249For a 1250pipeline, the process ID is that of the last command in the 1251pipeline. 1252If this parameter is referenced, the shell will remember 1253the process ID and its exit status until the 1254.Ic wait 1255built-in command reports completion of the process. 1256.It Li $0 1257(zero) Expands to the name of the shell script if passed on the command line, 1258the 1259.Ar name 1260operand if given (with 1261.Fl c ) 1262or otherwise argument 0 passed to the shell. 1263.El 1264.Ss Special Variables 1265The following variables are set by the shell or 1266have special meaning to it: 1267.Bl -tag -width ".Va HISTSIZE" 1268.It Va CDPATH 1269The search path used with the 1270.Ic cd 1271built-in. 1272.It Va EDITOR 1273The fallback editor used with the 1274.Ic fc 1275built-in. 1276If not set, the default editor is 1277.Xr ed 1 . 1278.It Va FCEDIT 1279The default editor used with the 1280.Ic fc 1281built-in. 1282.It Va HISTSIZE 1283The number of previous commands that are accessible. 1284.It Va HOME 1285The user's home directory, 1286used in tilde expansion and as a default directory for the 1287.Ic cd 1288built-in. 1289.It Va IFS 1290Input Field Separators. 1291The default value is 1292.Aq space , 1293.Aq tab , 1294and 1295.Aq newline 1296in that order. 1297This default also applies if 1298.Va IFS 1299is unset, but not if it is set to the empty string. 1300See the 1301.Sx White Space Splitting 1302section for more details. 1303.It Va LINENO 1304The current line number in the script or function. 1305.It Va MAIL 1306The name of a mail file, that will be checked for the arrival of new 1307mail. 1308Overridden by 1309.Va MAILPATH . 1310.It Va MAILPATH 1311A colon 1312.Pq Ql \&: 1313separated list of file names, for the shell to check for incoming 1314mail. 1315This variable overrides the 1316.Va MAIL 1317setting. 1318There is a maximum of 10 mailboxes that can be monitored at once. 1319.It Va PATH 1320The default search path for executables. 1321See the 1322.Sx Path Search 1323section for details. 1324.It Va PPID 1325The parent process ID of the invoked shell. 1326This is set at startup 1327unless this variable is in the environment. 1328A later change of parent process ID is not reflected. 1329A subshell retains the same value of 1330.Va PPID . 1331.It Va PS1 1332The primary prompt string, which defaults to 1333.Dq Li "$ " , 1334unless you are the superuser, in which case it defaults to 1335.Dq Li "# " . 1336.It Va PS2 1337The secondary prompt string, which defaults to 1338.Dq Li "> " . 1339.It Va PS4 1340The prefix for the trace output (if 1341.Fl x 1342is active). 1343The default is 1344.Dq Li "+ " . 1345.El 1346.Ss Word Expansions 1347This clause describes the various expansions that are 1348performed on words. 1349Not all expansions are performed on 1350every word, as explained later. 1351.Pp 1352Tilde expansions, parameter expansions, command substitutions, 1353arithmetic expansions, and quote removals that occur within 1354a single word expand to a single field. 1355It is only field 1356splitting or pathname expansion that can create multiple 1357fields from a single word. 1358The single exception to this rule is 1359the expansion of the special parameter 1360.Va @ 1361within double-quotes, 1362as was described above. 1363.Pp 1364The order of word expansion is: 1365.Bl -enum 1366.It 1367Tilde Expansion, Parameter Expansion, Command Substitution, 1368Arithmetic Expansion (these all occur at the same time). 1369.It 1370Field Splitting is performed on fields generated by step (1) 1371unless the 1372.Va IFS 1373variable is null. 1374.It 1375Pathname Expansion (unless the 1376.Fl f 1377option is in effect). 1378.It 1379Quote Removal. 1380.El 1381.Pp 1382The 1383.Ql $ 1384character is used to introduce parameter expansion, command 1385substitution, or arithmetic expansion. 1386.Ss Tilde Expansion (substituting a user's home directory) 1387A word beginning with an unquoted tilde character 1388.Pq Ql ~ 1389is 1390subjected to tilde expansion. 1391All the characters up to a slash 1392.Pq Ql / 1393or the end of the word are treated as a username 1394and are replaced with the user's home directory. 1395If the 1396username is missing (as in 1397.Pa ~/foobar ) , 1398the tilde is replaced with the value of the 1399.Va HOME 1400variable (the current user's home directory). 1401.Ss Parameter Expansion 1402The format for parameter expansion is as follows: 1403.Pp 1404.D1 Li ${ Ns Ar expression Ns Li } 1405.Pp 1406where 1407.Ar expression 1408consists of all characters until the matching 1409.Ql } . 1410Any 1411.Ql } 1412escaped by a backslash or within a single-quoted or double-quoted 1413string, and characters in 1414embedded arithmetic expansions, command substitutions, and variable 1415expansions, are not examined in determining the matching 1416.Ql } . 1417If the variants with 1418.Ql + , 1419.Ql - , 1420.Ql = 1421or 1422.Ql ?\& 1423occur within a double-quoted string, 1424as an extension there may be unquoted parts 1425(via double-quotes inside the expansion); 1426.Ql } 1427within such parts are also not examined in determining the matching 1428.Ql } . 1429.Pp 1430The simplest form for parameter expansion is: 1431.Pp 1432.D1 Li ${ Ns Ar parameter Ns Li } 1433.Pp 1434The value, if any, of 1435.Ar parameter 1436is substituted. 1437.Pp 1438The parameter name or symbol can be enclosed in braces, which are 1439optional except for positional parameters with more than one digit or 1440when parameter is followed by a character that could be interpreted as 1441part of the name. 1442If a parameter expansion occurs inside double-quotes: 1443.Bl -enum 1444.It 1445Field splitting is not performed on the results of the 1446expansion, with the exception of the special parameter 1447.Va @ . 1448.It 1449Pathname expansion is not performed on the results of the 1450expansion. 1451.El 1452.Pp 1453In addition, a parameter expansion can be modified by using one of the 1454following formats. 1455.Bl -tag -width indent 1456.It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li } 1457Use Default Values. 1458If 1459.Ar parameter 1460is unset or null, the expansion of 1461.Ar word 1462is substituted; otherwise, the value of 1463.Ar parameter 1464is substituted. 1465.It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li } 1466Assign Default Values. 1467If 1468.Ar parameter 1469is unset or null, the expansion of 1470.Ar word 1471is assigned to 1472.Ar parameter . 1473In all cases, the 1474final value of 1475.Ar parameter 1476is substituted. 1477Quoting inside 1478.Ar word 1479does not prevent field splitting or pathname expansion. 1480Only variables, not positional 1481parameters or special parameters, can be 1482assigned in this way. 1483.It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li } 1484Indicate Error if Null or Unset. 1485If 1486.Ar parameter 1487is unset or null, the expansion of 1488.Ar word 1489(or a message indicating it is unset if 1490.Ar word 1491is omitted) is written to standard 1492error and the shell exits with a nonzero 1493exit status. 1494Otherwise, the value of 1495.Ar parameter 1496is substituted. 1497An 1498interactive shell need not exit. 1499.It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li } 1500Use Alternate Value. 1501If 1502.Ar parameter 1503is unset or null, null is substituted; 1504otherwise, the expansion of 1505.Ar word 1506is substituted. 1507.El 1508.Pp 1509In the parameter expansions shown previously, use of the colon in the 1510format results in a test for a parameter that is unset or null; omission 1511of the colon results in a test for a parameter that is only unset. 1512.Pp 1513The 1514.Ar word 1515inherits the type of quoting 1516(unquoted, double-quoted or here-document) 1517from the surroundings, 1518with the exception that a backslash that quotes a closing brace is removed 1519during quote removal. 1520.Bl -tag -width indent 1521.It Li ${# Ns Ar parameter Ns Li } 1522String Length. 1523The length in characters of 1524the value of 1525.Ar parameter . 1526.El 1527.Pp 1528The following four varieties of parameter expansion provide for substring 1529processing. 1530In each case, pattern matching notation 1531(see 1532.Sx Shell Patterns ) , 1533rather than regular expression notation, 1534is used to evaluate the patterns. 1535If parameter is one of the special parameters 1536.Va * 1537or 1538.Va @ , 1539the result of the expansion is unspecified. 1540Enclosing the full parameter expansion string in double-quotes does not 1541cause the following four varieties of pattern characters to be quoted, 1542whereas quoting characters within the braces has this effect. 1543.Bl -tag -width indent 1544.It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li } 1545Remove Smallest Suffix Pattern. 1546The 1547.Ar word 1548is expanded to produce a pattern. 1549The 1550parameter expansion then results in 1551.Ar parameter , 1552with the smallest portion of the 1553suffix matched by the pattern deleted. 1554.It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li } 1555Remove Largest Suffix Pattern. 1556The 1557.Ar word 1558is expanded to produce a pattern. 1559The 1560parameter expansion then results in 1561.Ar parameter , 1562with the largest portion of the 1563suffix matched by the pattern deleted. 1564.It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li } 1565Remove Smallest Prefix Pattern. 1566The 1567.Ar word 1568is expanded to produce a pattern. 1569The 1570parameter expansion then results in 1571.Ar parameter , 1572with the smallest portion of the 1573prefix matched by the pattern deleted. 1574.It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li } 1575Remove Largest Prefix Pattern. 1576The 1577.Ar word 1578is expanded to produce a pattern. 1579The 1580parameter expansion then results in 1581.Ar parameter , 1582with the largest portion of the 1583prefix matched by the pattern deleted. 1584.El 1585.Ss Command Substitution 1586Command substitution allows the output of a command to be substituted in 1587place of the command name itself. 1588Command substitution occurs when 1589the command is enclosed as follows: 1590.Pp 1591.D1 Li $( Ns Ar command Ns Li )\& 1592.Pp 1593or the backquoted version: 1594.Pp 1595.D1 Li ` Ns Ar command Ns Li ` 1596.Pp 1597The shell expands the command substitution by executing command 1598and replacing the command substitution 1599with the standard output of the command, 1600removing sequences of one or more newlines at the end of the substitution. 1601Embedded newlines before the end of the output are not removed; 1602however, during field splitting, they may be translated into spaces 1603depending on the value of 1604.Va IFS 1605and the quoting that is in effect. 1606The command is executed in a subshell environment, 1607except that the built-in commands 1608.Ic jobid , 1609.Ic jobs , 1610and 1611.Ic trap 1612return information about the parent shell environment 1613and 1614.Ic times 1615returns information about the same process 1616if they are the only command in a command substitution. 1617.Ss Arithmetic Expansion 1618Arithmetic expansion provides a mechanism for evaluating an arithmetic 1619expression and substituting its value. 1620The format for arithmetic expansion is as follows: 1621.Pp 1622.D1 Li $(( Ns Ar expression Ns Li )) 1623.Pp 1624The 1625.Ar expression 1626is treated as if it were in double-quotes, except 1627that a double-quote inside the expression is not treated specially. 1628The 1629shell expands all tokens in the 1630.Ar expression 1631for parameter expansion, 1632command substitution, 1633arithmetic expansion 1634and quote removal. 1635.Pp 1636The allowed expressions are a subset of C expressions, 1637summarized below. 1638.Bl -tag -width "Variables" -offset indent 1639.It Values 1640All values are of type 1641.Ft intmax_t . 1642.It Constants 1643Decimal, octal (starting with 1644.Li 0 ) 1645and hexadecimal (starting with 1646.Li 0x ) 1647integer constants. 1648.It Variables 1649Shell variables can be read and written 1650and contain integer constants. 1651.It Unary operators 1652.Li "! ~ + -" 1653.It Binary operators 1654.Li "* / % + - << >> < <= > >= == != & ^ | && ||" 1655.It Assignment operators 1656.Li "= += -= *= /= %= <<= >>= &= ^= |=" 1657.It Conditional operator 1658.Li "? :" 1659.El 1660.Pp 1661The result of the expression is substituted in decimal. 1662.Ss White Space Splitting (Field Splitting) 1663In certain contexts, 1664after parameter expansion, command substitution, and 1665arithmetic expansion the shell scans the results of 1666expansions and substitutions that did not occur in double-quotes for 1667field splitting and multiple fields can result. 1668.Pp 1669Characters in 1670.Va IFS 1671that are whitespace 1672.Po 1673.Aq space , 1674.Aq tab , 1675and 1676.Aq newline 1677.Pc 1678are treated differently from other characters in 1679.Va IFS . 1680.Pp 1681Whitespace in 1682.Va IFS 1683at the beginning or end of a word is discarded. 1684.Pp 1685Subsequently, a field is delimited by either 1686.Bl -enum 1687.It 1688a non-whitespace character in 1689.Va IFS 1690with any whitespace in 1691.Va IFS 1692surrounding it, or 1693.It 1694one or more whitespace characters in 1695.Va IFS . 1696.El 1697.Pp 1698If a word ends with a non-whitespace character in 1699.Va IFS , 1700there is no empty field after this character. 1701.Pp 1702If no field is delimited, the word is discarded. 1703In particular, if a word consists solely of an unquoted substitution 1704and the result of the substitution is null, 1705it is removed by field splitting even if 1706.Va IFS 1707is null. 1708.Ss Pathname Expansion (File Name Generation) 1709Unless the 1710.Fl f 1711option is set, 1712file name generation is performed 1713after word splitting is complete. 1714Each word is 1715viewed as a series of patterns, separated by slashes. 1716The 1717process of expansion replaces the word with the names of 1718all existing files whose names can be formed by replacing 1719each pattern with a string that matches the specified pattern. 1720There are two restrictions on this: first, a pattern cannot match 1721a string containing a slash, and second, 1722a pattern cannot match a string starting with a period 1723unless the first character of the pattern is a period. 1724The next section describes the patterns used for 1725Pathname Expansion, 1726the four varieties of parameter expansion for substring processing and the 1727.Ic case 1728command. 1729.Ss Shell Patterns 1730A pattern consists of normal characters, which match themselves, 1731and meta-characters. 1732The meta-characters are 1733.Ql * , 1734.Ql \&? , 1735and 1736.Ql \&[ . 1737These characters lose their special meanings if they are quoted. 1738When command or variable substitution is performed and the dollar sign 1739or back quotes are not double-quoted, the value of the 1740variable or the output of the command is scanned for these 1741characters and they are turned into meta-characters. 1742.Pp 1743An asterisk 1744.Pq Ql * 1745matches any string of characters. 1746A question mark 1747.Pq Ql \&? 1748matches any single character. 1749A left bracket 1750.Pq Ql \&[ 1751introduces a character class. 1752The end of the character class is indicated by a 1753.Ql \&] ; 1754if the 1755.Ql \&] 1756is missing then the 1757.Ql \&[ 1758matches a 1759.Ql \&[ 1760rather than introducing a character class. 1761A character class matches any of the characters between the square brackets. 1762A locale-dependent range of characters may be specified using a minus sign. 1763A named class of characters (see 1764.Xr wctype 3 ) 1765may be specified by surrounding the name with 1766.Ql \&[: 1767and 1768.Ql :\&] . 1769For example, 1770.Ql \&[\&[:alpha:\&]\&] 1771is a shell pattern that matches a single letter. 1772The character class may be complemented by making an exclamation point 1773.Pq Ql !\& 1774the first character of the character class. 1775A caret 1776.Pq Ql ^ 1777has the same effect but is non-standard. 1778.Pp 1779To include a 1780.Ql \&] 1781in a character class, make it the first character listed 1782(after the 1783.Ql \&! 1784or 1785.Ql ^ , 1786if any). 1787To include a 1788.Ql - , 1789make it the first or last character listed. 1790.Ss Built-in Commands 1791This section lists the built-in commands. 1792.Bl -tag -width indent 1793.It Ic \&: 1794A null command that returns a 0 (true) exit value. 1795.It Ic \&. Ar file 1796The commands in the specified file are read and executed by the shell. 1797The 1798.Ic return 1799command may be used to return to the 1800.Ic \&. 1801command's caller. 1802If 1803.Ar file 1804contains any 1805.Ql / 1806characters, it is used as is. 1807Otherwise, the shell searches the 1808.Va PATH 1809for the file. 1810If it is not found in the 1811.Va PATH , 1812it is sought in the current working directory. 1813.It Ic \&[ 1814A built-in equivalent of 1815.Xr test 1 . 1816.It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc Ar ... Oc 1817If 1818.Ar name Ns = Ns Ar string 1819is specified, the shell defines the alias 1820.Ar name 1821with value 1822.Ar string . 1823If just 1824.Ar name 1825is specified, the value of the alias 1826.Ar name 1827is printed. 1828With no arguments, the 1829.Ic alias 1830built-in command prints the names and values of all defined aliases 1831(see 1832.Ic unalias ) . 1833Alias values are written with appropriate quoting so that they are 1834suitable for re-input to the shell. 1835Also see the 1836.Sx Aliases 1837subsection. 1838.It Ic bg Op Ar job ... 1839Continue the specified jobs 1840(or the current job if no jobs are given) 1841in the background. 1842.It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc 1843List or alter key bindings for the line editor. 1844This command is documented in 1845.Xr editrc 5 . 1846.It Ic break Op Ar num 1847See the 1848.Sx Flow-Control Constructs 1849subsection. 1850.It Ic builtin Ar cmd Op Ar arg ... 1851Execute the specified built-in command, 1852.Ar cmd . 1853This is useful when the user wishes to override a shell function 1854with the same name as a built-in command. 1855.It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory 1856Switch to the specified 1857.Ar directory , 1858or to the directory specified in the 1859.Va HOME 1860environment variable if no 1861.Ar directory 1862is specified. 1863If 1864.Ar directory 1865does not begin with 1866.Pa / , \&. , 1867or 1868.Pa .. , 1869then the directories listed in the 1870.Va CDPATH 1871variable will be 1872searched for the specified 1873.Ar directory . 1874If 1875.Va CDPATH 1876is unset, the current directory is searched. 1877The format of 1878.Va CDPATH 1879is the same as that of 1880.Va PATH . 1881In an interactive shell, 1882the 1883.Ic cd 1884command will print out the name of the directory 1885that it actually switched to 1886if this is different from the name that the user gave. 1887These may be different either because the 1888.Va CDPATH 1889mechanism was used or because a symbolic link was crossed. 1890.Pp 1891If the 1892.Fl P 1893option is specified, 1894.Pa .. 1895is handled physically and symbolic links are resolved before 1896.Pa .. 1897components are processed. 1898If the 1899.Fl L 1900option is specified, 1901.Pa .. 1902is handled logically. 1903This is the default. 1904.Pp 1905The 1906.Fl e 1907option causes 1908.Ic cd 1909to return exit status 1 if the full pathname of the new directory 1910cannot be determined reliably or at all. 1911Normally this is not considered an error, 1912although a warning is printed. 1913.It Ic chdir 1914A synonym for the 1915.Ic cd 1916built-in command. 1917.It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ... 1918.It Ic command Oo Fl p Oc Fl v Ar utility 1919.It Ic command Oo Fl p Oc Fl V Ar utility 1920The first form of invocation executes the specified 1921.Ar utility , 1922ignoring shell functions in the search. 1923If 1924.Ar utility 1925is a special builtin, 1926it is executed as if it were a regular builtin. 1927.Pp 1928If the 1929.Fl p 1930option is specified, the command search is performed using a 1931default value of 1932.Va PATH 1933that is guaranteed to find all of the standard utilities. 1934.Pp 1935If the 1936.Fl v 1937option is specified, 1938.Ar utility 1939is not executed but a description of its interpretation by the shell is 1940printed. 1941For ordinary commands the output is the path name; for shell built-in 1942commands, shell functions and keywords only the name is written. 1943Aliases are printed as 1944.Dq Ic alias Ar name Ns = Ns Ar value . 1945.Pp 1946The 1947.Fl V 1948option is identical to 1949.Fl v 1950except for the output. 1951It prints 1952.Dq Ar utility Ic is Ar description 1953where 1954.Ar description 1955is either 1956the path name to 1957.Ar utility , 1958a special shell builtin, 1959a shell builtin, 1960a shell function, 1961a shell keyword 1962or 1963an alias for 1964.Ar value . 1965.It Ic continue Op Ar num 1966See the 1967.Sx Flow-Control Constructs 1968subsection. 1969.It Ic echo Oo Fl e | n Oc Op Ar string ... 1970Print a space-separated list of the arguments to the standard output 1971and append a newline character. 1972.Bl -tag -width indent 1973.It Fl n 1974Suppress the output of the trailing newline. 1975.It Fl e 1976Process C-style backslash escape sequences. 1977The 1978.Ic echo 1979command understands the following character escapes: 1980.Bl -tag -width indent 1981.It \ea 1982Alert (ring the terminal bell) 1983.It \eb 1984Backspace 1985.It \ec 1986Suppress the trailing newline (this has the side-effect of truncating the 1987line if it is not the last character) 1988.It \ee 1989The ESC character 1990.Tn ( ASCII 19910x1b) 1992.It \ef 1993Formfeed 1994.It \en 1995Newline 1996.It \er 1997Carriage return 1998.It \et 1999Horizontal tab 2000.It \ev 2001Vertical tab 2002.It \e\e 2003Literal backslash 2004.It \e0nnn 2005(Zero) The character whose octal value is 2006.Ar nnn 2007.El 2008.Pp 2009If 2010.Ar string 2011is not enclosed in quotes then the backslash itself must be escaped 2012with a backslash to protect it from the shell. 2013For example 2014.Bd -literal -offset indent 2015$ echo -e "a\evb" 2016a 2017 b 2018$ echo -e a\e\evb 2019a 2020 b 2021$ echo -e "a\e\eb" 2022a\eb 2023$ echo -e a\e\e\e\eb 2024a\eb 2025.Ed 2026.El 2027.Pp 2028Only one of the 2029.Fl e 2030and 2031.Fl n 2032options may be specified. 2033.It Ic eval Ar string ... 2034Concatenate all the arguments with spaces. 2035Then re-parse and execute the command. 2036.It Ic exec Op Ar command Op Ar arg ... 2037Unless 2038.Ar command 2039is omitted, 2040the shell process is replaced with the specified program 2041(which must be a real program, not a shell built-in command or function). 2042Any redirections on the 2043.Ic exec 2044command are marked as permanent, 2045so that they are not undone when the 2046.Ic exec 2047command finishes. 2048.It Ic exit Op Ar exitstatus 2049Terminate the shell process. 2050If 2051.Ar exitstatus 2052is given 2053it is used as the exit status of the shell. 2054Otherwise, if the shell is executing an 2055.Cm EXIT 2056trap, the exit status of the last command before the trap is used; 2057if the shell is executing a trap for a signal, 2058the shell exits by resending the signal to itself. 2059Otherwise, the exit status of the preceding command is used. 2060The exit status should be an integer between 0 and 255. 2061.It Ic export Ar name ... 2062.It Ic export Op Fl p 2063The specified names are exported so that they will 2064appear in the environment of subsequent commands. 2065The only way to un-export a variable is to 2066.Ic unset 2067it. 2068The shell allows the value of a variable to be set 2069at the same time as it is exported by writing 2070.Pp 2071.D1 Ic export Ar name Ns = Ns Ar value 2072.Pp 2073With no arguments the 2074.Ic export 2075command lists the names 2076of all exported variables. 2077If the 2078.Fl p 2079option is specified, the exported variables are printed as 2080.Dq Ic export Ar name Ns = Ns Ar value 2081lines, suitable for re-input to the shell. 2082.It Ic false 2083A null command that returns a non-zero (false) exit value. 2084.It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last 2085.It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last 2086.It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first 2087The 2088.Ic fc 2089built-in command lists, or edits and re-executes, 2090commands previously entered to an interactive shell. 2091.Bl -tag -width indent 2092.It Fl e Ar editor 2093Use the editor named by 2094.Ar editor 2095to edit the commands. 2096The 2097.Ar editor 2098string is a command name, 2099subject to search via the 2100.Va PATH 2101variable. 2102The value in the 2103.Va FCEDIT 2104variable is used as a default when 2105.Fl e 2106is not specified. 2107If 2108.Va FCEDIT 2109is null or unset, the value of the 2110.Va EDITOR 2111variable is used. 2112If 2113.Va EDITOR 2114is null or unset, 2115.Xr ed 1 2116is used as the editor. 2117.It Fl l No (ell) 2118List the commands rather than invoking 2119an editor on them. 2120The commands are written in the 2121sequence indicated by the 2122.Ar first 2123and 2124.Ar last 2125operands, as affected by 2126.Fl r , 2127with each command preceded by the command number. 2128.It Fl n 2129Suppress command numbers when listing with 2130.Fl l . 2131.It Fl r 2132Reverse the order of the commands listed 2133(with 2134.Fl l ) 2135or edited 2136(with neither 2137.Fl l 2138nor 2139.Fl s ) . 2140.It Fl s 2141Re-execute the command without invoking an editor. 2142.It Ar first 2143.It Ar last 2144Select the commands to list or edit. 2145The number of previous commands that can be accessed 2146are determined by the value of the 2147.Va HISTSIZE 2148variable. 2149The value of 2150.Ar first 2151or 2152.Ar last 2153or both are one of the following: 2154.Bl -tag -width indent 2155.It Oo Cm + Oc Ns Ar num 2156A positive number representing a command number; 2157command numbers can be displayed with the 2158.Fl l 2159option. 2160.It Fl Ar num 2161A negative decimal number representing the 2162command that was executed 2163.Ar num 2164of 2165commands previously. 2166For example, \-1 is the immediately previous command. 2167.It Ar string 2168A string indicating the most recently entered command 2169that begins with that string. 2170If the 2171.Ar old Ns = Ns Ar new 2172operand is not also specified with 2173.Fl s , 2174the string form of the first operand cannot contain an embedded equal sign. 2175.El 2176.El 2177.Pp 2178The following variables affect the execution of 2179.Ic fc : 2180.Bl -tag -width ".Va HISTSIZE" 2181.It Va FCEDIT 2182Name of the editor to use for history editing. 2183.It Va HISTSIZE 2184The number of previous commands that are accessible. 2185.El 2186.It Ic fg Op Ar job 2187Move the specified 2188.Ar job 2189or the current job to the foreground. 2190.It Ic getopts Ar optstring var 2191The 2192.Tn POSIX 2193.Ic getopts 2194command. 2195The 2196.Ic getopts 2197command deprecates the older 2198.Xr getopt 1 2199command. 2200The first argument should be a series of letters, each possibly 2201followed by a colon which indicates that the option takes an argument. 2202The specified variable is set to the parsed option. 2203The index of 2204the next argument is placed into the shell variable 2205.Va OPTIND . 2206If an option takes an argument, it is placed into the shell variable 2207.Va OPTARG . 2208If an invalid option is encountered, 2209.Ar var 2210is set to 2211.Ql \&? . 2212It returns a false value (1) when it encounters the end of the options. 2213.It Ic hash Oo Fl rv Oc Op Ar command ... 2214The shell maintains a hash table which remembers the locations of commands. 2215With no arguments whatsoever, the 2216.Ic hash 2217command prints out the contents of this table. 2218Entries which have not been looked at since the last 2219.Ic cd 2220command are marked with an asterisk; 2221it is possible for these entries to be invalid. 2222.Pp 2223With arguments, the 2224.Ic hash 2225command removes each specified 2226.Ar command 2227from the hash table (unless they are functions) and then locates it. 2228With the 2229.Fl v 2230option, 2231.Ic hash 2232prints the locations of the commands as it finds them. 2233The 2234.Fl r 2235option causes the 2236.Ic hash 2237command to delete all the entries in the hash table except for functions. 2238.It Ic jobid Op Ar job 2239Print the process IDs of the processes in the specified 2240.Ar job . 2241If the 2242.Ar job 2243argument is omitted, use the current job. 2244.It Ic jobs Oo Fl lps Oc Op Ar job ... 2245Print information about the specified jobs, or all jobs if no 2246.Ar job 2247argument is given. 2248The information printed includes job ID, status and command name. 2249.Pp 2250If the 2251.Fl l 2252option is specified, the PID of each job is also printed. 2253If the 2254.Fl p 2255option is specified, only the process IDs for the process group leaders 2256are printed, one per line. 2257If the 2258.Fl s 2259option is specified, only the PIDs of the job commands are printed, one per 2260line. 2261.It Ic kill 2262A built-in equivalent of 2263.Xr kill 1 2264that additionally supports sending signals to jobs. 2265.It Ic local Oo Ar variable ... Oc Op Fl 2266See the 2267.Sx Functions 2268subsection. 2269.It Ic printf 2270A built-in equivalent of 2271.Xr printf 1 . 2272.It Ic pwd Op Fl L | P 2273Print the path of the current directory. 2274The built-in command may 2275differ from the program of the same name because the 2276built-in command remembers what the current directory 2277is rather than recomputing it each time. 2278This makes 2279it faster. 2280However, if the current directory is 2281renamed, 2282the built-in version of 2283.Xr pwd 1 2284will continue to print the old name for the directory. 2285.Pp 2286If the 2287.Fl P 2288option is specified, symbolic links are resolved. 2289If the 2290.Fl L 2291option is specified, the shell's notion of the current directory 2292is printed (symbolic links are not resolved). 2293This is the default. 2294.It Ic read Oo Fl p Ar prompt Oc Oo 2295.Fl t Ar timeout Oc Oo Fl er Oc Ar variable ... 2296The 2297.Ar prompt 2298is printed if the 2299.Fl p 2300option is specified 2301and the standard input is a terminal. 2302Then a line is 2303read from the standard input. 2304The trailing newline 2305is deleted from the line and the line is split as 2306described in the section on 2307.Sx White Space Splitting (Field Splitting) 2308above, and 2309the pieces are assigned to the variables in order. 2310If there are more pieces than variables, the remaining 2311pieces (along with the characters in 2312.Va IFS 2313that separated them) 2314are assigned to the last variable. 2315If there are more variables than pieces, the remaining 2316variables are assigned the null string. 2317.Pp 2318Backslashes are treated specially, unless the 2319.Fl r 2320option is 2321specified. 2322If a backslash is followed by 2323a newline, the backslash and the newline will be 2324deleted. 2325If a backslash is followed by any other 2326character, the backslash will be deleted and the following 2327character will be treated as though it were not in 2328.Va IFS , 2329even if it is. 2330.Pp 2331If the 2332.Fl t 2333option is specified and the 2334.Ar timeout 2335elapses before a complete line of input is supplied, 2336the 2337.Ic read 2338command will return an exit status of 1 without assigning any values. 2339The 2340.Ar timeout 2341value may optionally be followed by one of 2342.Ql s , 2343.Ql m 2344or 2345.Ql h 2346to explicitly specify seconds, minutes or hours. 2347If none is supplied, 2348.Ql s 2349is assumed. 2350.Pp 2351The 2352.Fl e 2353option exists only for backward compatibility with older scripts. 2354.It Ic readonly Oo Fl p Oc Op Ar name ... 2355Each specified 2356.Ar name 2357is marked as read only, 2358so that it cannot be subsequently modified or unset. 2359The shell allows the value of a variable to be set 2360at the same time as it is marked read only 2361by using the following form: 2362.Pp 2363.D1 Ic readonly Ar name Ns = Ns Ar value 2364.Pp 2365With no arguments the 2366.Ic readonly 2367command lists the names of all read only variables. 2368If the 2369.Fl p 2370option is specified, the read-only variables are printed as 2371.Dq Ic readonly Ar name Ns = Ns Ar value 2372lines, suitable for re-input to the shell. 2373.It Ic return Op Ar exitstatus 2374See the 2375.Sx Functions 2376subsection. 2377.It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo 2378.Fl c Ar string Oc Op Fl - Ar arg ... 2379The 2380.Ic set 2381command performs three different functions: 2382.Bl -item 2383.It 2384With no arguments, it lists the values of all shell variables. 2385.It 2386If options are given, 2387either in short form or using the long 2388.Dq Fl /+o Ar longname 2389form, 2390it sets or clears the specified options as described in the section called 2391.Sx Argument List Processing . 2392.It 2393If the 2394.Dq Fl - 2395option is specified, 2396.Ic set 2397will replace the shell's positional parameters with the subsequent 2398arguments. 2399If no arguments follow the 2400.Dq Fl - 2401option, 2402all the positional parameters will be cleared, 2403which is equivalent to executing the command 2404.Dq Li "shift $#" . 2405The 2406.Dq Fl - 2407flag may be omitted when specifying arguments to be used 2408as positional replacement parameters. 2409This is not recommended, 2410because the first argument may begin with a dash 2411.Pq Ql - 2412or a plus 2413.Pq Ql + , 2414which the 2415.Ic set 2416command will interpret as a request to enable or disable options. 2417.El 2418.It Ic setvar Ar variable value 2419Assigns the specified 2420.Ar value 2421to the specified 2422.Ar variable . 2423The 2424.Ic setvar 2425command is intended to be used in functions that 2426assign values to variables whose names are passed as parameters. 2427In general it is better to write 2428.Dq Ar variable Ns = Ns Ar value 2429rather than using 2430.Ic setvar . 2431.It Ic shift Op Ar n 2432Shift the positional parameters 2433.Ar n 2434times, or once if 2435.Ar n 2436is not specified. 2437A shift sets the value of 2438.Li $1 2439to the value of 2440.Li $2 , 2441the value of 2442.Li $2 2443to the value of 2444.Li $3 , 2445and so on, 2446decreasing the value of 2447.Li $# 2448by one. 2449If there are zero positional parameters, shifting does not do anything. 2450.It Ic test 2451A built-in equivalent of 2452.Xr test 1 . 2453.It Ic times 2454Print the amount of time spent executing the shell process and its children. 2455The first output line shows the user and system times for the shell process 2456itself, the second one contains the user and system times for the 2457children. 2458.It Ic trap Oo Ar action Oc Ar signal ... 2459.It Ic trap Fl l 2460Cause the shell to parse and execute 2461.Ar action 2462when any specified 2463.Ar signal 2464is received. 2465The signals are specified by name or number. 2466In addition, the pseudo-signal 2467.Cm EXIT 2468may be used to specify an 2469.Ar action 2470that is performed when the shell terminates. 2471The 2472.Ar action 2473may be an empty string or a dash 2474.Pq Ql - ; 2475the former causes the specified signal to be ignored 2476and the latter causes the default action to be taken. 2477Omitting the 2478.Ar action 2479is another way to request the default action, for compatibility reasons this 2480usage is not recommended though. 2481In a subshell or utility environment, 2482the shell resets trapped (but not ignored) signals to the default action. 2483The 2484.Ic trap 2485command has no effect on signals that were ignored on entry to the shell. 2486.Pp 2487Option 2488.Fl l 2489causes the 2490.Ic trap 2491command to display a list of valid signal names. 2492.It Ic true 2493A null command that returns a 0 (true) exit value. 2494.It Ic type Op Ar name ... 2495Interpret each 2496.Ar name 2497as a command and print the resolution of the command search. 2498Possible resolutions are: 2499shell keyword, alias, special shell builtin, shell builtin, command, 2500tracked alias 2501and not found. 2502For aliases the alias expansion is printed; 2503for commands and tracked aliases 2504the complete pathname of the command is printed. 2505.It Ic ulimit Oo Fl HSabcdflmnstuv Oc Op Ar limit 2506Set or display resource limits (see 2507.Xr getrlimit 2 ) . 2508If 2509.Ar limit 2510is specified, the named resource will be set; 2511otherwise the current resource value will be displayed. 2512.Pp 2513If 2514.Fl H 2515is specified, the hard limits will be set or displayed. 2516While everybody is allowed to reduce a hard limit, 2517only the superuser can increase it. 2518The 2519.Fl S 2520option 2521specifies the soft limits instead. 2522When displaying limits, 2523only one of 2524.Fl S 2525or 2526.Fl H 2527can be given. 2528The default is to display the soft limits, 2529and to set both the hard and the soft limits. 2530.Pp 2531Option 2532.Fl a 2533causes the 2534.Ic ulimit 2535command to display all resources. 2536The parameter 2537.Ar limit 2538is not acceptable in this mode. 2539.Pp 2540The remaining options specify which resource value is to be 2541displayed or modified. 2542They are mutually exclusive. 2543.Bl -tag -width indent 2544.It Fl b Ar sbsize 2545The maximum size of socket buffer usage, in bytes. 2546.It Fl c Ar coredumpsize 2547The maximal size of core dump files, in 512-byte blocks. 2548.It Fl d Ar datasize 2549The maximal size of the data segment of a process, in kilobytes. 2550.It Fl f Ar filesize 2551The maximal size of a file, in 512-byte blocks. 2552.It Fl l Ar lockedmem 2553The maximal size of memory that can be locked by a process, in 2554kilobytes. 2555.It Fl m Ar memoryuse 2556The maximal resident set size of a process, in kilobytes. 2557.It Fl n Ar nofiles 2558The maximal number of descriptors that could be opened by a process. 2559.It Fl s Ar stacksize 2560The maximal size of the stack segment, in kilobytes. 2561.It Fl t Ar time 2562The maximal amount of CPU time to be used by each process, in seconds. 2563.It Fl u Ar userproc 2564The maximal number of simultaneous processes for this user ID. 2565.It Fl v Ar virtualmem 2566The maximal virtual size of a process, in kilobytes. 2567.El 2568.It Ic umask Oo Fl S Oc Op Ar mask 2569Set the file creation mask (see 2570.Xr umask 2 ) 2571to the octal or symbolic (see 2572.Xr chmod 1 ) 2573value specified by 2574.Ar mask . 2575If the argument is omitted, the current mask value is printed. 2576If the 2577.Fl S 2578option is specified, the output is symbolic, otherwise the output is octal. 2579.It Ic unalias Oo Fl a Oc Op Ar name ... 2580The specified alias names are removed. 2581If 2582.Fl a 2583is specified, all aliases are removed. 2584.It Ic unset Oo Fl fv Oc Ar name ... 2585The specified variables or functions are unset and unexported. 2586If the 2587.Fl v 2588option is specified or no options are given, the 2589.Ar name 2590arguments are treated as variable names. 2591If the 2592.Fl f 2593option is specified, the 2594.Ar name 2595arguments are treated as function names. 2596.It Ic wait Op Ar job 2597Wait for the specified 2598.Ar job 2599to complete and return the exit status of the last process in the 2600.Ar job . 2601If the argument is omitted, wait for all jobs to complete 2602and return an exit status of zero. 2603.El 2604.Ss Commandline Editing 2605When 2606.Nm 2607is being used interactively from a terminal, the current command 2608and the command history 2609(see 2610.Ic fc 2611in 2612.Sx Built-in Commands ) 2613can be edited using 2614.Nm vi Ns -mode 2615command line editing. 2616This mode uses commands similar 2617to a subset of those described in the 2618.Xr vi 1 2619man page. 2620The command 2621.Dq Li "set -o vi" 2622(or 2623.Dq Li "set -V" ) 2624enables 2625.Nm vi Ns -mode 2626editing and places 2627.Nm 2628into 2629.Nm vi 2630insert mode. 2631With 2632.Nm vi Ns -mode 2633enabled, 2634.Nm 2635can be switched between insert mode and command mode by typing 2636.Aq ESC . 2637Hitting 2638.Aq return 2639while in command mode will pass the line to the shell. 2640.Pp 2641Similarly, the 2642.Dq Li "set -o emacs" 2643(or 2644.Dq Li "set -E" ) 2645command can be used to enable a subset of 2646.Nm emacs Ns -style 2647command line editing features. 2648.Sh ENVIRONMENT 2649The following environment variables affect the execution of 2650.Nm : 2651.Bl -tag -width ".Ev LANGXXXXXX" 2652.It Ev ENV 2653Initialization file for interactive shells. 2654.It Ev LANG , Ev LC_* 2655Locale settings. 2656These are inherited by children of the shell, 2657and is used in a limited manner by the shell itself. 2658.It Ev PWD 2659An absolute pathname for the current directory, 2660possibly containing symbolic links. 2661This is used and updated by the shell. 2662.It Ev TERM 2663The default terminal setting for the shell. 2664This is inherited by children of the shell, and is used in the history 2665editing modes. 2666.El 2667.Pp 2668Additionally, all environment variables are turned into shell variables 2669at startup, 2670which may affect the shell as described under 2671.Sx Special Variables . 2672.Sh EXIT STATUS 2673Errors that are detected by the shell, such as a syntax error, will 2674cause the shell to exit with a non-zero exit status. 2675If the shell is not an interactive shell, the execution of the shell 2676file will be aborted. 2677Otherwise the shell will return the exit status of the last command 2678executed, or if the 2679.Ic exit 2680builtin is used with a numeric argument, it 2681will return the argument. 2682.Sh SEE ALSO 2683.Xr builtin 1 , 2684.Xr chsh 1 , 2685.Xr echo 1 , 2686.Xr ed 1 , 2687.Xr emacs 1 Pq Pa pkgsrc/editors/emacs , 2688.Xr kill 1 , 2689.Xr printf 1 , 2690.Xr pwd 1 , 2691.Xr test 1 , 2692.Xr vi 1 , 2693.Xr execve 2 , 2694.Xr getrlimit 2 , 2695.Xr umask 2 , 2696.Xr wctype 3 , 2697.Xr editrc 5 , 2698.Xr script 7 2699.Sh HISTORY 2700A 2701.Nm 2702command, the Thompson shell, appeared in 2703.At v1 . 2704It was superseded in 2705.At v7 2706by the Bourne shell, which inherited the name 2707.Nm . 2708.Pp 2709This version of 2710.Nm 2711was rewritten in 1989 under the 2712.Bx 2713license after the Bourne shell from 2714.At V.4 . 2715.Sh AUTHORS 2716This version of 2717.Nm 2718was originally written by 2719.An Kenneth Almquist . 2720.Sh BUGS 2721The 2722.Nm 2723utility does not recognize multibyte characters other than UTF-8. 2724Splitting using 2725.Va IFS 2726and the line editing library 2727.Xr editline 3 2728do not recognize multibyte characters. 2729.Pp 2730The characters generated by filename completion should probably be quoted 2731to ensure that the filename is still valid after the input line has been 2732processed. 2733