1.\"- 2.\" SPDX-License-Identifier: BSD-3-Clause 3.\" 4.\" Copyright (c) 1991, 1993 5.\" The Regents of the University of California. All rights reserved. 6.\" 7.\" This code is derived from software contributed to Berkeley by 8.\" Kenneth Almquist. 9.\" 10.\" Redistribution and use in source and binary forms, with or without 11.\" modification, are permitted provided that the following conditions 12.\" are met: 13.\" 1. Redistributions of source code must retain the above copyright 14.\" notice, this list of conditions and the following disclaimer. 15.\" 2. Redistributions in binary form must reproduce the above copyright 16.\" notice, this list of conditions and the following disclaimer in the 17.\" documentation and/or other materials provided with the distribution. 18.\" 3. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.Dd November 20, 2024 35.Dt SH 1 36.Os 37.Sh NAME 38.Nm sh 39.Nd command interpreter (shell) 40.Sh SYNOPSIS 41.Nm 42.Op Fl /+abCEefhIilmnPpTuVvx 43.Op Fl /+o Ar longname 44.Oo 45.Ar script 46.Op Ar arg ... 47.Oc 48.Nm 49.Op Fl /+abCEefhIilmnPpTuVvx 50.Op Fl /+o Ar longname 51.Fl c Ar string 52.Oo 53.Ar name 54.Op Ar arg ... 55.Oc 56.Nm 57.Op Fl /+abCEefhIilmnPpTuVvx 58.Op Fl /+o Ar longname 59.Fl s 60.Op Ar arg ... 61.Sh DESCRIPTION 62The 63.Nm 64utility is the standard command interpreter for the system. 65The current version of 66.Nm 67is close to the 68.St -p1003.1 69specification for the shell. 70It only supports features 71designated by POSIX, 72plus a few Berkeley extensions. 73This man page is not intended to be a tutorial nor a complete 74specification of the shell. 75.Ss Overview 76The shell is a command that reads lines from 77either a file or the terminal, interprets them, and 78generally executes other commands. 79It is the program that is started when a user logs into the system, 80although a user can select a different shell with the 81.Xr chsh 1 82command. 83The shell 84implements a language that has flow control constructs, 85a macro facility that provides a variety of features in 86addition to data storage, along with built-in history and line 87editing capabilities. 88It incorporates many features to 89aid interactive use and has the advantage that the interpretative 90language is common to both interactive and non-interactive 91use (shell scripts). 92That is, commands can be typed directly 93to the running shell or can be put into a file, 94which can be executed directly by the shell. 95.Ss Invocation 96.\" 97.\" XXX This next sentence is incredibly confusing. 98.\" 99If no arguments are present and if the standard input of the shell 100is connected to a terminal 101(or if the 102.Fl i 103option is set), 104the shell is considered an interactive shell. 105An interactive shell 106generally prompts before each command and handles programming 107and command errors differently (as described below). 108When first starting, the shell inspects argument 0, and 109if it begins with a dash 110.Pq Ql - , 111the shell is also considered a login shell. 112This is normally done automatically by the system 113when the user first logs in. 114A login shell first reads commands 115from the files 116.Pa /etc/profile 117and then 118.Pa .profile 119in a user's home directory, 120if they exist. 121If the environment variable 122.Ev ENV 123is set on entry to a shell, or is set in the 124.Pa .profile 125of a login shell, the shell then subjects its value to parameter expansion 126and arithmetic expansion and reads commands from the named file. 127Therefore, a user should place commands that are to be executed only 128at login time in the 129.Pa .profile 130file, and commands that are executed for every shell inside the 131.Ev ENV 132file. 133The user can set the 134.Ev ENV 135variable to some file by placing the following line in the file 136.Pa .profile 137in the home directory, 138substituting for 139.Pa .shrc 140the filename desired: 141.Pp 142.Dl "ENV=$HOME/.shrc; export ENV" 143.Pp 144The first non-option argument specified on the command line 145will be treated as the 146name of a file from which to read commands (a shell script), and 147the remaining arguments are set as the positional parameters 148of the shell 149.Li ( $1 , $2 , 150etc.). 151Otherwise, the shell reads commands 152from its standard input. 153.Pp 154Unlike older versions of 155.Nm 156the 157.Ev ENV 158script is only sourced on invocation of interactive shells. 159This 160closes a well-known, and sometimes easily exploitable security 161hole related to poorly thought out 162.Ev ENV 163scripts. 164.Ss Argument List Processing 165All of the single letter options to 166.Nm 167have a corresponding long name, 168with the exception of 169.Fl c 170and 171.Fl /+o . 172These long names are provided next to the single letter options 173in the descriptions below. 174The long name for an option may be specified as an argument to the 175.Fl /+o 176option of 177.Nm . 178Once the shell is running, 179the long name for an option may be specified as an argument to the 180.Fl /+o 181option of the 182.Ic set 183built-in command 184(described later in the section called 185.Sx Built-in Commands ) . 186Introducing an option with a dash 187.Pq Ql - 188enables the option, 189while using a plus 190.Pq Ql + 191disables the option. 192A 193.Dq Li -- 194or plain 195.Ql - 196will stop option processing and will force the remaining 197words on the command line to be treated as arguments. 198The 199.Fl /+o 200and 201.Fl c 202options do not have long names. 203They take arguments and are described after the single letter options. 204.Bl -tag -width indent 205.It Fl a Li allexport 206Flag variables for export when assignments are made to them. 207.It Fl b Li notify 208Enable asynchronous notification of background job 209completion. 210(UNIMPLEMENTED) 211.It Fl C Li noclobber 212Do not overwrite existing files with 213.Ql > . 214.It Fl E Li emacs 215Enable the built-in 216.Xr emacs 1 Pq Pa ports/editors/emacs 217command line editor (disables the 218.Fl V 219option if it has been set; 220set automatically when interactive on terminals). 221.It Fl e Li errexit 222Exit immediately if any untested command fails in non-interactive mode. 223The exit status of a command is considered to be 224explicitly tested if the command is part of the list used to control 225an 226.Ic if , elif , while , 227or 228.Ic until ; 229if the command is the left 230hand operand of an 231.Dq Li && 232or 233.Dq Li || 234operator; or if the command is a pipeline preceded by the 235.Ic !\& 236keyword. 237If a shell function is executed and its exit status is explicitly 238tested, all commands of the function are considered to be tested as 239well. 240.Pp 241It is recommended to check for failures explicitly 242instead of relying on 243.Fl e 244because it tends to behave in unexpected ways, 245particularly in larger scripts. 246.It Fl f Li noglob 247Disable pathname expansion. 248.It Fl h Li trackall 249A do-nothing option for POSIX compliance. 250.It Fl I Li ignoreeof 251Ignore 252.Dv EOF Ap s 253from input when in interactive mode. 254.It Fl i Li interactive 255Force the shell to behave interactively. 256.It Fl l 257Force the shell to act as if it has been invoked as a login shell. 258.It Fl m Li monitor 259Turn on job control (set automatically when interactive). 260A new process group is created for each pipeline (called a job). 261It is possible to suspend jobs or to have them run in the foreground or 262in the background. 263In a non-interactive shell, 264this option can be set even if no terminal is available 265and is useful to place processes in separate process groups. 266.It Fl n Li noexec 267If not interactive, read commands but do not 268execute them. 269This is useful for checking the 270syntax of shell scripts. 271.It Fl P Li physical 272Change the default for the 273.Ic cd 274and 275.Ic pwd 276commands from 277.Fl L 278(logical directory layout) 279to 280.Fl P 281(physical directory layout). 282.It Fl p Li privileged 283Turn on privileged mode. 284This mode is enabled on startup 285if either the effective user or group ID is not equal to the 286real user or group ID. 287Turning this mode off sets the 288effective user and group IDs to the real user and group IDs. 289When this mode is enabled for interactive shells, the file 290.Pa /etc/suid_profile 291is sourced instead of 292.Pa ~/.profile 293after 294.Pa /etc/profile 295is sourced, and the contents of the 296.Ev ENV 297variable are ignored. 298.It Fl s Li stdin 299Read commands from standard input (set automatically 300if no file arguments are present). 301This option has 302no effect when set after the shell has already started 303running (i.e., when set with the 304.Ic set 305command). 306.It Fl T Li trapsasync 307When waiting for a child, execute traps immediately. 308If this option is not set, 309traps are executed after the child exits, 310as specified in 311.St -p1003.2 . 312This nonstandard option is useful for putting guarding shells around 313children that block signals. 314The surrounding shell may kill the child 315or it may just return control to the tty and leave the child alone, 316like this: 317.Bd -literal -offset indent 318sh -T -c "trap 'exit 1' 2 ; some-blocking-program" 319.Ed 320.It Fl u Li nounset 321Write a message to standard error when attempting 322to expand a variable, a positional parameter or 323the special parameter 324.Va \&! 325that is not set, and if the 326shell is not interactive, exit immediately. 327.It Fl V Li vi 328Enable the built-in 329.Xr vi 1 330command line editor (disables 331.Fl E 332if it has been set). 333.It Fl v Li verbose 334The shell writes its input to standard error 335as it is read. 336Useful for debugging. 337.It Fl x Li xtrace 338Write each command 339(preceded by the value of the 340.Va PS4 341variable subjected to parameter expansion and arithmetic expansion) 342to standard error before it is executed. 343Useful for debugging. 344.It Li nolog 345Another do-nothing option for POSIX compliance. 346It only has a long name. 347.It Li pipefail 348Change the exit status of a pipeline to the last non-zero exit status of 349any command in the pipeline, if any. 350Since an exit due to 351.Dv SIGPIPE 352counts as a non-zero exit status, 353this option may cause non-zero exit status for successful pipelines 354if a command such as 355.Xr head 1 356in the pipeline terminates with status 0 without reading its 357input completely. 358This option only has a long name. 359.It Li verify 360Set 361.Dv O_VERIFY 362when sourcing files or loading profiles. 363.\" See also 364.\" .Xr mac_veriexec 4 . TODO Does not exist; write it. 365.El 366.Pp 367The 368.Fl c 369option causes the commands to be read from the 370.Ar string 371operand instead of from the standard input. 372Keep in mind that this option only accepts a single string as its 373argument, hence multi-word strings must be quoted. 374.Pp 375The 376.Fl /+o 377option takes as its only argument the long name of an option 378to be enabled or disabled. 379For example, the following two invocations of 380.Nm 381both enable the built-in 382.Xr emacs 1 Pq Pa ports/editors/emacs 383command line editor: 384.Bd -literal -offset indent 385set -E 386set -o emacs 387.Ed 388.Pp 389If used without an argument, the 390.Fl o 391option displays the current option settings in a human-readable format. 392If 393.Cm +o 394is used without an argument, the current option settings are output 395in a format suitable for re-input into the shell. 396.Ss Lexical Structure 397The shell reads input in terms of lines from a file and breaks 398it up into words at whitespace (blanks and tabs), and at 399certain sequences of 400characters called 401.Dq operators , 402which are special to the shell. 403There are two types of operators: control operators and 404redirection operators (their meaning is discussed later). 405The following is a list of valid operators: 406.Bl -tag -width indent 407.It Control operators: 408.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 409.It Li & Ta Li && Ta Li \&( Ta Li \&) Ta Li \en 410.It Li ;; Ta Li ;& Ta Li \&; Ta Li \&| Ta Li || 411.El 412.It Redirection operators: 413.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 414.It Li < Ta Li > Ta Li << Ta Li >> Ta Li <> 415.It Li <& Ta Li >& Ta Li <<- Ta Li >| Ta \& 416.El 417.El 418.Pp 419The character 420.Ql # 421introduces a comment if used at the beginning of a word. 422The word starting with 423.Ql # 424and the rest of the line are ignored. 425.Pp 426ASCII 427.Dv NUL 428characters (character code 0) are not allowed in shell input. 429.Ss Quoting 430Quoting is used to remove the special meaning of certain characters 431or words to the shell, such as operators, whitespace, keywords, 432or alias names. 433.Pp 434There are four types of quoting: matched single quotes, 435dollar-single quotes, 436matched double quotes, and backslash. 437.Bl -tag -width indent 438.It Single Quotes 439Enclosing characters in single quotes preserves the literal 440meaning of all the characters (except single quotes, making 441it impossible to put single-quotes in a single-quoted string). 442.It Dollar-Single Quotes 443Enclosing characters between 444.Li $' 445and 446.Li ' 447preserves the literal meaning of all characters 448except backslashes and single quotes. 449A backslash introduces a C-style escape sequence: 450.Bl -tag -width xUnnnnnnnn 451.It \ea 452Alert (ring the terminal bell) 453.It \eb 454Backspace 455.It \ec Ns Ar c 456The control character denoted by 457.Li ^ Ns Ar c 458in 459.Xr stty 1 . 460If 461.Ar c 462is a backslash, it must be doubled. 463.It \ee 464The ESC character (ASCII 0x1b) 465.It \ef 466Formfeed 467.It \en 468Newline 469.It \er 470Carriage return 471.It \et 472Horizontal tab 473.It \ev 474Vertical tab 475.It \e\e 476Literal backslash 477.It \e\&' 478Literal single-quote 479.It \e\&" 480Literal double-quote 481.It \e Ns Ar nnn 482The byte whose octal value is 483.Ar nnn 484(one to three digits) 485.It \ex Ns Ar nn 486The byte whose hexadecimal value is 487.Ar nn 488(one or more digits only the last two of which are used) 489.It \eu Ns Ar nnnn 490The Unicode code point 491.Ar nnnn 492(four hexadecimal digits) 493.It \eU Ns Ar nnnnnnnn 494The Unicode code point 495.Ar nnnnnnnn 496(eight hexadecimal digits) 497.El 498.Pp 499The sequences for Unicode code points are currently only useful with 500UTF-8 locales. 501They reject code point 0 and UTF-16 surrogates. 502.Pp 503If an escape sequence would produce a byte with value 0, 504that byte and the rest of the string until the matching single-quote 505are ignored. 506.Pp 507Any other string starting with a backslash is an error. 508.It Double Quotes 509Enclosing characters within double quotes preserves the literal 510meaning of all characters except dollar sign 511.Pq Ql $ , 512backquote 513.Pq Ql ` , 514and backslash 515.Pq Ql \e . 516The backslash inside double quotes is historically weird. 517It remains literal unless it precedes the following characters, 518which it serves to quote: 519.Pp 520.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 521.It Li $ Ta Li ` Ta Li \&" Ta Li \e Ta Li \en 522.El 523.It Backslash 524A backslash preserves the literal meaning of the following 525character, with the exception of the newline character 526.Pq Ql \en . 527A backslash preceding a newline is treated as a line continuation. 528.El 529.Ss Keywords 530Keywords or reserved words are words that have special meaning to the 531shell and are recognized at the beginning of a line and 532after a control operator. 533The following are keywords: 534.Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center 535.It Li \&! Ta { Ta } Ta Ic case Ta Ic do 536.It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi 537.It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while 538.El 539.Ss Aliases 540An alias is a name and corresponding value set using the 541.Ic alias 542built-in command. 543Wherever the command word of a simple command may occur, 544and after checking for keywords if a keyword may occur, the shell 545checks the word to see if it matches an alias. 546If it does, it replaces it in the input stream with its value. 547For example, if there is an alias called 548.Dq Li lf 549with the value 550.Dq Li "ls -F" , 551then the input 552.Pp 553.Dl "lf foobar" 554.Pp 555would become 556.Pp 557.Dl "ls -F foobar" 558.Pp 559Aliases are also recognized after an alias 560whose value ends with a space or tab. 561For example, if there is also an alias called 562.Dq Li nohup 563with the value 564.Dq Li "nohup " , 565then the input 566.Pp 567.Dl "nohup lf foobar" 568.Pp 569would become 570.Pp 571.Dl "nohup ls -F foobar" 572.Pp 573Aliases provide a convenient way for naive users to 574create shorthands for commands without having to learn how 575to create functions with arguments. 576Using aliases in scripts is discouraged 577because the command that defines them must be executed 578before the code that uses them is parsed. 579This is fragile and not portable. 580.Pp 581An alias name may be escaped in a command line, so that it is not 582replaced by its alias value, by using quoting characters within or 583adjacent to the alias name. 584This is most often done by prefixing 585an alias name with a backslash to execute a function, built-in, or 586normal program with the same name. 587See the 588.Sx Quoting 589subsection. 590.Ss Commands 591The shell interprets the words it reads according to a 592language, the specification of which is outside the scope 593of this man page (refer to the BNF in the 594.St -p1003.2 595document). 596Essentially though, a line is read and if 597the first word of the line (or after a control operator) 598is not a keyword, then the shell has recognized a 599simple command. 600Otherwise, a complex command or some 601other special construct may have been recognized. 602.Ss Simple Commands 603If a simple command has been recognized, the shell performs 604the following actions: 605.Bl -enum 606.It 607Leading words of the form 608.Dq Li name=value 609are stripped off and assigned to the environment of 610the simple command 611(they do not affect expansions). 612Redirection operators and 613their arguments (as described below) are stripped 614off and saved for processing. 615.It 616The remaining words are expanded as described in 617the section called 618.Sx Word Expansions , 619and the first remaining word is considered the command 620name and the command is located. 621The remaining 622words are considered the arguments of the command. 623If no command name resulted, then the 624.Dq Li name=value 625variable assignments recognized in 1) affect the 626current shell. 627.It 628Redirections are performed as described in 629the next section. 630.El 631.Ss Redirections 632Redirections are used to change where a command reads its input 633or sends its output. 634In general, redirections open, close, or 635duplicate an existing reference to a file. 636The overall format 637used for redirection is: 638.Pp 639.D1 Oo Ar n Oc Ar redir-op file 640.Pp 641The 642.Ar redir-op 643is one of the redirection operators mentioned 644previously. 645The following gives some examples of how these 646operators can be used. 647Note that stdin and stdout are commonly used abbreviations 648for standard input and standard output respectively. 649.Bl -tag -width "1234567890XX" -offset indent 650.It Oo Ar n Oc Ns Li > Ar file 651redirect stdout (or file descriptor 652.Ar n ) 653to 654.Ar file 655.It Oo Ar n Oc Ns Li >| Ar file 656same as above, but override the 657.Fl C 658option 659.It Oo Ar n Oc Ns Li >> Ar file 660append stdout (or file descriptor 661.Ar n ) 662to 663.Ar file 664.It Oo Ar n Oc Ns Li < Ar file 665redirect stdin (or file descriptor 666.Ar n ) 667from 668.Ar file 669.It Oo Ar n Oc Ns Li <> Ar file 670redirect stdin (or file descriptor 671.Ar n ) 672to and from 673.Ar file 674.It Oo Ar n1 Oc Ns Li <& Ns Ar n2 675duplicate stdin (or file descriptor 676.Ar n1 ) 677from file descriptor 678.Ar n2 679.It Oo Ar n Oc Ns Li <&- 680close stdin (or file descriptor 681.Ar n ) 682.It Oo Ar n1 Oc Ns Li >& Ns Ar n2 683duplicate stdout (or file descriptor 684.Ar n1 ) 685to file descriptor 686.Ar n2 687.It Oo Ar n Oc Ns Li >&- 688close stdout (or file descriptor 689.Ar n ) 690.El 691.Pp 692The following redirection is often called a 693.Dq here-document . 694.Bd -unfilled -offset indent 695.Oo Ar n Oc Ns Li << Ar delimiter 696.Ar here-doc-text 697.Ar ... 698.Ar delimiter 699.Ed 700.Pp 701All the text on successive lines up to the delimiter is 702saved away and made available to the command on standard 703input, or file descriptor 704.Ar n 705if it is specified. 706If the 707.Ar delimiter 708as specified on the initial line is quoted, then the 709.Ar here-doc-text 710is treated literally, otherwise the text is subjected to 711parameter expansion, command substitution, and arithmetic 712expansion (as described in the section on 713.Sx Word Expansions ) . 714If the operator is 715.Dq Li <<- 716instead of 717.Dq Li << , 718then leading tabs 719in the 720.Ar here-doc-text 721are stripped. 722.Ss Search and Execution 723There are three types of commands: shell functions, 724built-in commands, and normal programs. 725The command is searched for (by name) in that order. 726The three types of commands are all executed in a different way. 727.Pp 728When a shell function is executed, all of the shell positional 729parameters (except 730.Li $0 , 731which remains unchanged) are 732set to the arguments of the shell function. 733The variables which are explicitly placed in the environment of 734the command (by placing assignments to them before the 735function name) are made local to the function and are set 736to the values given. 737Then the command given in the function definition is executed. 738The positional parameters are restored to their original values 739when the command completes. 740This all occurs within the current shell. 741.Pp 742Shell built-in commands are executed internally to the shell, without 743spawning a new process. 744There are two kinds of built-in commands: regular and special. 745Assignments before special builtins persist after they finish 746executing and assignment errors, redirection errors and certain 747operand errors cause a script to be aborted. 748Special builtins cannot be overridden with a function. 749Both regular and special builtins can affect the shell in ways 750normal programs cannot. 751.Pp 752Otherwise, if the command name does not match a function 753or built-in command, the command is searched for as a normal 754program in the file system (as described in the next section). 755When a normal program is executed, the shell runs the program, 756passing the arguments and the environment to the program. 757If the program is not a normal executable file 758(i.e., if it does not begin with the 759.Dq "magic number" 760whose ASCII representation is 761.Dq Li #! , 762resulting in an 763.Er ENOEXEC 764return value from 765.Xr execve 2 ) 766but appears to be a text file, 767the shell will run a new instance of 768.Nm 769to interpret it. 770.Pp 771Note that previous versions of this document 772and the source code itself misleadingly and sporadically 773refer to a shell script without a magic number 774as a 775.Dq "shell procedure" . 776.Ss Path Search 777When locating a command, the shell first looks to see if 778it has a shell function by that name. 779Then it looks for a 780built-in command by that name. 781If a built-in command is not found, 782one of two things happen: 783.Bl -enum 784.It 785Command names containing a slash are simply executed without 786performing any searches. 787.It 788The shell searches each entry in the 789.Va PATH 790variable 791in turn for the command. 792The value of the 793.Va PATH 794variable should be a series of 795entries separated by colons. 796Each entry consists of a 797directory name. 798The current directory 799may be indicated implicitly by an empty directory name, 800or explicitly by a single period. 801.El 802.Ss Command Exit Status 803Each command has an exit status that can influence the behavior 804of other shell commands. 805The paradigm is that a command exits 806with zero for normal or success, and non-zero for failure, 807error, or a false indication. 808The man page for each command 809should indicate the various exit codes and what they mean. 810Additionally, the built-in commands return exit codes, as does 811an executed shell function. 812.Pp 813If a command is terminated by a signal, its exit status is greater than 128. 814The signal name can be found by passing the exit status to 815.Li kill -l . 816.Pp 817If there is no command word, 818the exit status is the exit status of the last command substitution executed, 819or zero if the command does not contain any command substitutions. 820.Ss Complex Commands 821Complex commands are combinations of simple commands 822with control operators or keywords, together creating a larger complex 823command. 824More generally, a command is one of the following: 825.Bl -item -offset indent 826.It 827simple command 828.It 829pipeline 830.It 831list or compound-list 832.It 833compound command 834.It 835function definition 836.El 837.Pp 838Unless otherwise stated, the exit status of a command is 839that of the last simple command executed by the command, 840or zero if no simple command was executed. 841.Ss Pipelines 842A pipeline is a sequence of one or more commands separated 843by the control operator 844.Ql \&| . 845The standard output of all but 846the last command is connected to the standard input 847of the next command. 848The standard output of the last 849command is inherited from the shell, as usual. 850.Pp 851The format for a pipeline is: 852.Pp 853.D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ... 854.Pp 855The standard output of 856.Ar command1 857is connected to the standard input of 858.Ar command2 . 859The standard input, standard output, or 860both of a command is considered to be assigned by the 861pipeline before any redirection specified by redirection 862operators that are part of the command. 863.Pp 864Note that unlike some other shells, 865.Nm 866executes each process in a pipeline with more than one command 867in a subshell environment and as a child of the 868.Nm 869process. 870.Pp 871If the pipeline is not in the background (discussed later), 872the shell waits for all commands to complete. 873.Pp 874If the keyword 875.Ic !\& 876does not precede the pipeline, the 877exit status is the exit status of the last command specified 878in the pipeline if the 879.Cm pipefail 880option is not set or all commands returned zero, 881or the last non-zero exit status of any command in the pipeline otherwise. 882Otherwise, the exit status is the logical 883NOT of that exit status. 884That is, if 885that status is zero, the exit status is 1; if 886that status is greater than zero, the exit status 887is zero. 888.Pp 889Because pipeline assignment of standard input or standard 890output or both takes place before redirection, it can be 891modified by redirection. 892For example: 893.Pp 894.Dl "command1 2>&1 | command2" 895.Pp 896sends both the standard output and standard error of 897.Ar command1 898to the standard input of 899.Ar command2 . 900.Pp 901A 902.Ql \&; 903or newline terminator causes the preceding 904AND-OR-list 905(described below in the section called 906.Sx Short-Circuit List Operators ) 907to be executed sequentially; 908an 909.Ql & 910causes asynchronous execution of the preceding AND-OR-list. 911.Ss Background Commands (&) 912If a command is terminated by the control operator ampersand 913.Pq Ql & , 914the shell executes the command in a subshell environment (see 915.Sx Grouping Commands Together 916below) and asynchronously; 917the shell does not wait for the command to finish 918before executing the next command. 919.Pp 920The format for running a command in background is: 921.Pp 922.D1 Ar command1 Li & Op Ar command2 Li & Ar ... 923.Pp 924If the shell is not interactive, the standard input of an 925asynchronous command is set to 926.Pa /dev/null . 927.Pp 928The exit status is zero. 929.Ss Lists (Generally Speaking) 930A list is a sequence of zero or more commands separated by 931newlines, semicolons, or ampersands, 932and optionally terminated by one of these three characters. 933The commands in a 934list are executed in the order they are written. 935If command is followed by an ampersand, the shell starts the 936command and immediately proceeds onto the next command; 937otherwise it waits for the command to terminate before 938proceeding to the next one. 939.Ss Short-Circuit List Operators 940.Dq Li && 941and 942.Dq Li || 943are AND-OR list operators. 944.Dq Li && 945executes the first command, and then executes the second command 946if the exit status of the first command is zero. 947.Dq Li || 948is similar, but executes the second command if the exit 949status of the first command is nonzero. 950.Dq Li && 951and 952.Dq Li || 953both have the same priority. 954.Ss Flow-Control Constructs (if, while, for, case) 955The syntax of the 956.Ic if 957command is: 958.Bd -unfilled -offset indent -compact 959.Ic if Ar list 960.Ic then Ar list 961.Oo Ic elif Ar list 962.Ic then Ar list Oc Ar ... 963.Op Ic else Ar list 964.Ic fi 965.Ed 966.Pp 967The exit status is that of selected 968.Ic then 969or 970.Ic else 971list, 972or zero if no list was selected. 973.Pp 974The syntax of the 975.Ic while 976command is: 977.Bd -unfilled -offset indent -compact 978.Ic while Ar list 979.Ic do Ar list 980.Ic done 981.Ed 982.Pp 983The two lists are executed repeatedly while the exit status of the 984first list is zero. 985The 986.Ic until 987command is similar, but has the word 988.Ic until 989in place of 990.Ic while , 991which causes it to 992repeat until the exit status of the first list is zero. 993.Pp 994The exit status is that of the last execution of the second list, 995or zero if it was never executed. 996.Pp 997The syntax of the 998.Ic for 999command is: 1000.Bd -unfilled -offset indent -compact 1001.Ic for Ar variable Op Ic in Ar word ... 1002.Ic do Ar list 1003.Ic done 1004.Ed 1005.Pp 1006If 1007.Ic in 1008and the following words are omitted, 1009.Ic in Li \&"$@\&" 1010is used instead. 1011The words are expanded, and then the list is executed 1012repeatedly with the variable set to each word in turn. 1013The 1014.Ic do 1015and 1016.Ic done 1017commands may be replaced with 1018.Ql { 1019and 1020.Ql } . 1021.Pp 1022The syntax of the 1023.Ic break 1024and 1025.Ic continue 1026commands is: 1027.D1 Ic break Op Ar num 1028.D1 Ic continue Op Ar num 1029.Pp 1030The 1031.Ic break 1032command terminates the 1033.Ar num 1034innermost 1035.Ic for 1036or 1037.Ic while 1038loops. 1039The 1040.Ic continue 1041command continues with the next iteration of the innermost loop. 1042These are implemented as special built-in commands. 1043.Pp 1044The syntax of the 1045.Ic case 1046command is: 1047.Bd -unfilled -offset indent -compact 1048.Ic case Ar word Ic in 1049.Ar pattern ) Ar list Li ;; 1050.Ar ... 1051.Ic esac 1052.Ed 1053.Pp 1054The pattern can actually be one or more patterns 1055(see 1056.Sx Shell Patterns 1057described later), 1058separated by 1059.Ql \&| 1060characters. 1061Tilde expansion, parameter expansion, command substitution, 1062arithmetic expansion and quote removal are applied to the word. 1063Then, each pattern is expanded in turn using tilde expansion, 1064parameter expansion, command substitution and arithmetic expansion and 1065the expanded form of the word is checked against it. 1066If a match is found, the corresponding list is executed. 1067If the selected list is terminated by the control operator 1068.Ql ;& 1069instead of 1070.Ql ;; , 1071execution continues with the next list, 1072continuing until a list terminated with 1073.Ql ;; 1074or the end of the 1075.Ic case 1076command. 1077.Ss Grouping Commands Together 1078Commands may be grouped by writing either 1079.Sm off 1080.Bd -literal -offset indent 1081.Po Ar list Pc 1082.Ed 1083.Sm on 1084.Pp 1085or 1086.Bd -literal -offset indent 1087.No { Ar list ; } 1088.Ed 1089.Pp 1090The first form executes the commands in a subshell environment. 1091A subshell environment has its own copy of: 1092.Bl -enum 1093.It 1094The current working directory as set by 1095.Ic cd . 1096.It 1097The file creation mask as set by 1098.Ic umask . 1099.It 1100Resource limits as set by 1101.Ic ulimit . 1102.It 1103References to open files. 1104.It 1105Traps as set by 1106.Ic trap . 1107.It 1108Known jobs. 1109.It 1110Positional parameters and variables. 1111.It 1112Shell options. 1113.It 1114Shell functions. 1115.It 1116Shell aliases. 1117.El 1118.Pp 1119These are copied from the parent shell environment, 1120except that trapped (but not ignored) signals are reset to the default action 1121and known jobs are cleared. 1122Any changes do not affect the parent shell environment. 1123.Pp 1124A subshell environment may be implemented as a child process or differently. 1125If job control is enabled in an interactive shell, 1126commands grouped in parentheses can be suspended and continued as a unit. 1127.Pp 1128For compatibility with other shells, 1129two open parentheses in sequence should be separated by whitespace. 1130.Pp 1131The second form never forks another shell, 1132so it is slightly more efficient. 1133Grouping commands together this way allows the user to 1134redirect their output as though they were one program: 1135.Bd -literal -offset indent 1136{ echo -n "hello"; echo " world"; } > greeting 1137.Ed 1138.Ss Functions 1139The syntax of a function definition is 1140.Pp 1141.D1 Ar name Li \&( \&) Ar command 1142.Pp 1143A function definition is an executable statement; when 1144executed it installs a function named 1145.Ar name 1146and returns an 1147exit status of zero. 1148The 1149.Ar command 1150is normally a list 1151enclosed between 1152.Ql { 1153and 1154.Ql } . 1155.Pp 1156Variables may be declared to be local to a function by 1157using the 1158.Ic local 1159command. 1160This should appear as the first statement of a function, 1161and the syntax is: 1162.Pp 1163.D1 Ic local Oo Ar variable ... Oc Op Fl 1164.Pp 1165The 1166.Ic local 1167command is implemented as a built-in command. 1168The exit status is zero 1169unless the command is not in a function or a variable name is invalid. 1170.Pp 1171When a variable is made local, it inherits the initial 1172value and exported and readonly flags from the variable 1173with the same name in the surrounding scope, if there is 1174one. 1175Otherwise, the variable is initially unset. 1176The shell 1177uses dynamic scoping, so that if the variable 1178.Va x 1179is made local to function 1180.Em f , 1181which then calls function 1182.Em g , 1183references to the variable 1184.Va x 1185made inside 1186.Em g 1187will refer to the variable 1188.Va x 1189declared inside 1190.Em f , 1191not to the global variable named 1192.Va x . 1193.Pp 1194The only special parameter that can be made local is 1195.Ql - . 1196Making 1197.Ql - 1198local causes any shell options 1199(including those that only have long names) 1200that are 1201changed via the 1202.Ic set 1203command inside the function to be 1204restored to their original values when the function 1205returns. 1206.Pp 1207The syntax of the 1208.Ic return 1209command is 1210.Pp 1211.D1 Ic return Op Ar exitstatus 1212.Pp 1213It terminates the current executional scope, returning from the closest 1214nested function or sourced script; 1215if no function or sourced script is being executed, 1216it exits the shell instance. 1217The 1218.Ic return 1219command is implemented as a special built-in command. 1220.Ss Variables and Parameters 1221The shell maintains a set of parameters. 1222A parameter 1223denoted by a name 1224(consisting solely 1225of alphabetics, numerics, and underscores, 1226and starting with an alphabetic or an underscore) 1227is called a variable. 1228When starting up, 1229the shell turns all environment variables with valid names into shell 1230variables. 1231New variables can be set using the form 1232.Pp 1233.D1 Ar name Ns = Ns Ar value 1234.Pp 1235A parameter can also be denoted by a number 1236or a special character as explained below. 1237.Pp 1238Assignments are expanded differently from other words: 1239tilde expansion is also performed after the equals sign and after any colon 1240and usernames are also terminated by colons, 1241and field splitting and pathname expansion are not performed. 1242.Pp 1243This special expansion applies not only to assignments that form a simple 1244command by themselves or precede a command word, 1245but also to words passed to the 1246.Ic export , 1247.Ic local 1248or 1249.Ic readonly 1250built-in commands that have this form. 1251For this, the builtin's name must be literal 1252(not the result of an expansion) 1253and may optionally be preceded by one or more literal instances of 1254.Ic command 1255without options. 1256.Ss Positional Parameters 1257A positional parameter is a parameter denoted by a number greater than zero. 1258The shell sets these initially to the values of its command line 1259arguments that follow the name of the shell script. 1260The 1261.Ic set 1262built-in command can also be used to set or reset them. 1263.Ss Special Parameters 1264Special parameters are parameters denoted by a single special character 1265or the digit zero. 1266They are shown in the following list, exactly as they would appear in input 1267typed by the user or in the source of a shell script. 1268.Bl -hang 1269.It Li $* 1270Expands to the positional parameters, starting from one. 1271When 1272the expansion occurs within a double-quoted string 1273it expands to a single field with the value of each parameter 1274separated by the first character of the 1275.Va IFS 1276variable, 1277or by a space if 1278.Va IFS 1279is unset. 1280.It Li $@ 1281Expands to the positional parameters, starting from one. 1282When 1283the expansion occurs within double-quotes, each positional 1284parameter expands as a separate argument. 1285If there are no positional parameters, the 1286expansion of 1287.Li @ 1288generates zero arguments, even when 1289.Li @ 1290is double-quoted. 1291What this basically means, for example, is 1292if 1293.Li $1 1294is 1295.Dq Li abc 1296and 1297.Li $2 1298is 1299.Dq Li "def ghi" , 1300then 1301.Li \&"$@\&" 1302expands to 1303the two arguments: 1304.Bd -literal -offset indent 1305"abc" "def ghi" 1306.Ed 1307.It Li $# 1308Expands to the number of positional parameters. 1309.It Li $? 1310Expands to the exit status of the most recent pipeline. 1311.It Li $- 1312(hyphen) Expands to the current option flags (the single-letter 1313option names concatenated into a string) as specified on 1314invocation, by the 1315.Ic set 1316built-in command, or implicitly 1317by the shell. 1318.It Li $$ 1319Expands to the process ID of the invoked shell. 1320A subshell 1321retains the same value of 1322.Va $ 1323as its parent. 1324.It Li $! 1325Expands to the process ID of the most recent background 1326command executed from the current shell. 1327For a 1328pipeline, the process ID is that of the last command in the 1329pipeline. 1330If this parameter is referenced, the shell will remember 1331the process ID and its exit status until the 1332.Ic wait 1333built-in command reports completion of the process. 1334.It Li $0 1335(zero) Expands to the name of the shell script if passed on the command line, 1336the 1337.Ar name 1338operand if given (with 1339.Fl c ) 1340or otherwise argument 0 passed to the shell. 1341.El 1342.Ss Special Variables 1343The following variables are set by the shell or 1344have special meaning to it: 1345.Bl -tag -width ".Va HISTSIZE" 1346.It Va CDPATH 1347The search path used with the 1348.Ic cd 1349built-in. 1350.It Va EDITOR 1351The fallback editor used with the 1352.Ic fc 1353built-in. 1354If not set, the default editor is 1355.Xr ed 1 . 1356.It Va FCEDIT 1357The default editor used with the 1358.Ic fc 1359built-in. 1360.It Va HISTFILE 1361File used for persistent history storage. 1362If unset 1363.Pa ~/.sh_history 1364will be used. 1365If set but empty or 1366.Va HISTSIZE 1367is set to 0 1368the shell will not load and save the history. 1369.It Va HISTSIZE 1370The number of previous commands that are accessible. 1371.It Va HOME 1372The user's home directory, 1373used in tilde expansion and as a default directory for the 1374.Ic cd 1375built-in. 1376.It Va IFS 1377Input Field Separators. 1378This is initialized at startup to 1379.Aq space , 1380.Aq tab , 1381and 1382.Aq newline 1383in that order. 1384This value also applies if 1385.Va IFS 1386is unset, but not if it is set to the empty string. 1387See the 1388.Sx White Space Splitting 1389section for more details. 1390.It Va LINENO 1391The current line number in the script or function. 1392.It Va MAIL 1393The name of a mail file, that will be checked for the arrival of new 1394mail. 1395Overridden by 1396.Va MAILPATH . 1397.It Va MAILPATH 1398A colon 1399.Pq Ql \&: 1400separated list of file names, for the shell to check for incoming 1401mail. 1402This variable overrides the 1403.Va MAIL 1404setting. 1405There is a maximum of 10 mailboxes that can be monitored at once. 1406.It Va OPTIND 1407The index of the next argument to be processed by 1408.Ic getopts . 1409This is initialized to 1 at startup. 1410.It Va PATH 1411The default search path for executables. 1412See the 1413.Sx Path Search 1414section for details. 1415.It Va PPID 1416The parent process ID of the invoked shell. 1417This is set at startup 1418unless this variable is in the environment. 1419A later change of parent process ID is not reflected. 1420A subshell retains the same value of 1421.Va PPID . 1422.It Va PS1 1423The primary prompt string, which defaults to 1424.Dq Li "$ " , 1425unless you are the superuser, in which case it defaults to 1426.Dq Li "# " . 1427.Va PS1 1428may include any of the following formatting sequences, 1429which are replaced by the given information: 1430.Bl -tag -width indent 1431.It Li \eD{format} 1432The current time in 1433.Xr strftime 3 1434.Ar format . 1435The braces are required. 1436Empty 1437.Ar format 1438is equivalent to 1439\&%X, 1440national representation of the time. 1441.It Li \eH 1442This system's fully-qualified hostname (FQDN). 1443.It Li \eh 1444This system's hostname. 1445.It Li \eu 1446User name. 1447.It Li \eW 1448The final component of the current working directory. 1449.It Li \ew 1450The entire path of the current working directory. 1451.It Li \e$ 1452Superuser status. 1453.Dq Li "$" 1454for normal users and 1455.Dq Li "#" 1456for superusers. 1457.It Li \e\e 1458A literal backslash. 1459.It Li \e[ 1460Start of a sequence of non-printing characters (used, for example, 1461to embed ANSI CSI sequences into the prompt). 1462.It Li \e] 1463End of a sequence of non-printing characters. 1464.El 1465.Pp 1466The following special and non-printing characters are supported 1467within the sequence of non-printing characters: 1468.Bl -tag -width indent 1469.It Li \ea 1470Emits ASCII BEL (0x07, 007) character. 1471.It Li \ee 1472Emits ASCII ESC (0x1b, 033) character. 1473.It Li \er 1474Emits ASCII CR (0x0d, 015) character. 1475.It Li \en 1476Emits CRLF sequence. 1477.El 1478.It Va PS2 1479The secondary prompt string, which defaults to 1480.Dq Li "> " . 1481.Va PS2 1482may include any of the formatting sequences from 1483.Va PS1 . 1484.It Va PS4 1485The prefix for the trace output (if 1486.Fl x 1487is active). 1488The default is 1489.Dq Li "+ " . 1490.El 1491.Ss Word Expansions 1492This clause describes the various expansions that are 1493performed on words. 1494Not all expansions are performed on 1495every word, as explained later. 1496.Pp 1497Tilde expansions, parameter expansions, command substitutions, 1498arithmetic expansions, and quote removals that occur within 1499a single word expand to a single field. 1500It is only field 1501splitting or pathname expansion that can create multiple 1502fields from a single word. 1503The single exception to this rule is 1504the expansion of the special parameter 1505.Va @ 1506within double-quotes, 1507as was described above. 1508.Pp 1509The order of word expansion is: 1510.Bl -enum 1511.It 1512Tilde Expansion, Parameter Expansion, Command Substitution, 1513Arithmetic Expansion (these all occur at the same time). 1514.It 1515Field Splitting is performed on fields generated by step (1) 1516unless the 1517.Va IFS 1518variable is null. 1519.It 1520Pathname Expansion (unless the 1521.Fl f 1522option is in effect). 1523.It 1524Quote Removal. 1525.El 1526.Pp 1527The 1528.Ql $ 1529character is used to introduce parameter expansion, command 1530substitution, or arithmetic expansion. 1531.Ss Tilde Expansion (substituting a user's home directory) 1532A word beginning with an unquoted tilde character 1533.Pq Ql ~ 1534is 1535subjected to tilde expansion. 1536All the characters up to a slash 1537.Pq Ql / 1538or the end of the word are treated as a username 1539and are replaced with the user's home directory. 1540If the 1541username is missing (as in 1542.Pa ~/foobar ) , 1543the tilde is replaced with the value of the 1544.Va HOME 1545variable (the current user's home directory). 1546.Ss Parameter Expansion 1547The format for parameter expansion is as follows: 1548.Pp 1549.D1 Li ${ Ns Ar expression Ns Li } 1550.Pp 1551where 1552.Ar expression 1553consists of all characters until the matching 1554.Ql } . 1555Any 1556.Ql } 1557escaped by a backslash or within a single-quoted or double-quoted 1558string, and characters in 1559embedded arithmetic expansions, command substitutions, and variable 1560expansions, are not examined in determining the matching 1561.Ql } . 1562If the variants with 1563.Ql + , 1564.Ql - , 1565.Ql = 1566or 1567.Ql ?\& 1568occur within a double-quoted string, 1569as an extension there may be unquoted parts 1570(via double-quotes inside the expansion); 1571.Ql } 1572within such parts are also not examined in determining the matching 1573.Ql } . 1574.Pp 1575The simplest form for parameter expansion is: 1576.Pp 1577.D1 Li ${ Ns Ar parameter Ns Li } 1578.Pp 1579The value, if any, of 1580.Ar parameter 1581is substituted. 1582.Pp 1583The parameter name or symbol can be enclosed in braces, which are 1584optional except for positional parameters with more than one digit or 1585when parameter is followed by a character that could be interpreted as 1586part of the name. 1587If a parameter expansion occurs inside double-quotes: 1588.Bl -enum 1589.It 1590Field splitting is not performed on the results of the 1591expansion, with the exception of the special parameter 1592.Va @ . 1593.It 1594Pathname expansion is not performed on the results of the 1595expansion. 1596.El 1597.Pp 1598In addition, a parameter expansion can be modified by using one of the 1599following formats. 1600.Bl -tag -width indent 1601.It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li } 1602Use Default Values. 1603If 1604.Ar parameter 1605is unset or null, the expansion of 1606.Ar word 1607is substituted; otherwise, the value of 1608.Ar parameter 1609is substituted. 1610.It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li } 1611Assign Default Values. 1612If 1613.Ar parameter 1614is unset or null, the expansion of 1615.Ar word 1616is assigned to 1617.Ar parameter . 1618In all cases, the 1619final value of 1620.Ar parameter 1621is substituted. 1622Quoting inside 1623.Ar word 1624does not prevent field splitting or pathname expansion. 1625Only variables, not positional 1626parameters or special parameters, can be 1627assigned in this way. 1628.It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li } 1629Indicate Error if Null or Unset. 1630If 1631.Ar parameter 1632is unset or null, the expansion of 1633.Ar word 1634(or a message indicating it is unset if 1635.Ar word 1636is omitted) is written to standard 1637error and the shell exits with a nonzero 1638exit status. 1639Otherwise, the value of 1640.Ar parameter 1641is substituted. 1642An 1643interactive shell need not exit. 1644.It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li } 1645Use Alternate Value. 1646If 1647.Ar parameter 1648is unset or null, null is substituted; 1649otherwise, the expansion of 1650.Ar word 1651is substituted. 1652.El 1653.Pp 1654In the parameter expansions shown previously, use of the colon in the 1655format results in a test for a parameter that is unset or null; omission 1656of the colon results in a test for a parameter that is only unset. 1657.Pp 1658The 1659.Ar word 1660inherits the type of quoting 1661(unquoted, double-quoted or here-document) 1662from the surroundings, 1663with the exception that a backslash that quotes a closing brace is removed 1664during quote removal. 1665.Bl -tag -width indent 1666.It Li ${# Ns Ar parameter Ns Li } 1667String Length. 1668The length in characters of 1669the value of 1670.Ar parameter . 1671.El 1672.Pp 1673The following four varieties of parameter expansion provide for substring 1674processing. 1675In each case, pattern matching notation 1676(see 1677.Sx Shell Patterns ) , 1678rather than regular expression notation, 1679is used to evaluate the patterns. 1680If parameter is one of the special parameters 1681.Va * 1682or 1683.Va @ , 1684the result of the expansion is unspecified. 1685Enclosing the full parameter expansion string in double-quotes does not 1686cause the following four varieties of pattern characters to be quoted, 1687whereas quoting characters within the braces has this effect. 1688.Bl -tag -width indent 1689.It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li } 1690Remove Smallest Suffix Pattern. 1691The 1692.Ar word 1693is expanded to produce a pattern. 1694The 1695parameter expansion then results in 1696.Ar parameter , 1697with the smallest portion of the 1698suffix matched by the pattern deleted. 1699.It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li } 1700Remove Largest Suffix Pattern. 1701The 1702.Ar word 1703is expanded to produce a pattern. 1704The 1705parameter expansion then results in 1706.Ar parameter , 1707with the largest portion of the 1708suffix matched by the pattern deleted. 1709.It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li } 1710Remove Smallest Prefix Pattern. 1711The 1712.Ar word 1713is expanded to produce a pattern. 1714The 1715parameter expansion then results in 1716.Ar parameter , 1717with the smallest portion of the 1718prefix matched by the pattern deleted. 1719.It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li } 1720Remove Largest Prefix Pattern. 1721The 1722.Ar word 1723is expanded to produce a pattern. 1724The 1725parameter expansion then results in 1726.Ar parameter , 1727with the largest portion of the 1728prefix matched by the pattern deleted. 1729.El 1730.Ss Command Substitution 1731Command substitution allows the output of a command to be substituted in 1732place of the command name itself. 1733Command substitution occurs when 1734the command is enclosed as follows: 1735.Pp 1736.D1 Li $( Ns Ar command Ns Li )\& 1737.Pp 1738or the backquoted version: 1739.Pp 1740.D1 Li ` Ns Ar command Ns Li ` 1741.Pp 1742The shell expands the command substitution by executing command 1743and replacing the command substitution 1744with the standard output of the command, 1745removing sequences of one or more newlines at the end of the substitution. 1746Embedded newlines before the end of the output are not removed; 1747however, during field splitting, they may be translated into spaces 1748depending on the value of 1749.Va IFS 1750and the quoting that is in effect. 1751The command is executed in a subshell environment, 1752except that the built-in commands 1753.Ic jobid , 1754.Ic jobs , 1755and 1756.Ic trap 1757return information about the parent shell environment 1758and 1759.Ic times 1760returns information about the same process 1761if they are the only command in a command substitution. 1762.Pp 1763If a command substitution of the 1764.Li $( 1765form begins with a subshell, 1766the 1767.Li $( 1768and 1769.Li (\& 1770must be separated by whitespace 1771to avoid ambiguity with arithmetic expansion. 1772.Ss Arithmetic Expansion 1773Arithmetic expansion provides a mechanism for evaluating an arithmetic 1774expression and substituting its value. 1775The format for arithmetic expansion is as follows: 1776.Pp 1777.D1 Li $(( Ns Ar expression Ns Li )) 1778.Pp 1779The 1780.Ar expression 1781is treated as if it were in double-quotes, except 1782that a double-quote inside the expression is not treated specially. 1783The 1784shell expands all tokens in the 1785.Ar expression 1786for parameter expansion, 1787command substitution, 1788arithmetic expansion 1789and quote removal. 1790.Pp 1791The allowed expressions are a subset of C expressions, 1792summarized below. 1793.Bl -tag -width "Variables" -offset indent 1794.It Values 1795All values are of type 1796.Ft intmax_t . 1797.It Constants 1798Decimal, octal (starting with 1799.Li 0 ) 1800and hexadecimal (starting with 1801.Li 0x ) 1802integer constants. 1803.It Variables 1804Shell variables can be read and written 1805and contain integer constants. 1806.It Unary operators 1807.Li "! ~ + -" 1808.It Binary operators 1809.Li "* / % + - << >> < <= > >= == != & ^ | && ||"\& 1810.It Assignment operators 1811.Li "= += -= *= /= %= <<= >>= &= ^= |=" 1812.It Conditional operator 1813.Li "? :"\& 1814.El 1815.Pp 1816The result of the expression is substituted in decimal. 1817.Ss White Space Splitting (Field Splitting) 1818In certain contexts, 1819after parameter expansion, command substitution, and 1820arithmetic expansion the shell scans the results of 1821expansions and substitutions that did not occur in double-quotes for 1822field splitting and multiple fields can result. 1823.Pp 1824Characters in 1825.Va IFS 1826that are whitespace 1827.Po 1828.Aq space , 1829.Aq tab , 1830and 1831.Aq newline 1832.Pc 1833are treated differently from other characters in 1834.Va IFS . 1835.Pp 1836Whitespace in 1837.Va IFS 1838at the beginning or end of a word is discarded. 1839.Pp 1840Subsequently, a field is delimited by either 1841.Bl -enum 1842.It 1843a non-whitespace character in 1844.Va IFS 1845with any whitespace in 1846.Va IFS 1847surrounding it, or 1848.It 1849one or more whitespace characters in 1850.Va IFS . 1851.El 1852.Pp 1853If a word ends with a non-whitespace character in 1854.Va IFS , 1855there is no empty field after this character. 1856.Pp 1857If no field is delimited, the word is discarded. 1858In particular, if a word consists solely of an unquoted substitution 1859and the result of the substitution is null, 1860it is removed by field splitting even if 1861.Va IFS 1862is null. 1863.Ss Pathname Expansion (File Name Generation) 1864Unless the 1865.Fl f 1866option is set, 1867file name generation is performed 1868after word splitting is complete. 1869Each word is 1870viewed as a series of patterns, separated by slashes. 1871The 1872process of expansion replaces the word with the names of 1873all existing files whose names can be formed by replacing 1874each pattern with a string that matches the specified pattern. 1875There are two restrictions on this: first, a pattern cannot match 1876a string containing a slash, and second, 1877a pattern cannot match a string starting with a period 1878unless the first character of the pattern is a period. 1879The next section describes the patterns used for 1880Pathname Expansion, 1881the four varieties of parameter expansion for substring processing and the 1882.Ic case 1883command. 1884.Ss Shell Patterns 1885A pattern consists of normal characters, which match themselves, 1886and meta-characters. 1887The meta-characters are 1888.Ql * , 1889.Ql \&? , 1890and 1891.Ql \&[ . 1892These characters lose their special meanings if they are quoted. 1893When command or variable substitution is performed and the dollar sign 1894or back quotes are not double-quoted, the value of the 1895variable or the output of the command is scanned for these 1896characters and they are turned into meta-characters. 1897.Pp 1898An asterisk 1899.Pq Ql * 1900matches any string of characters. 1901A question mark 1902.Pq Ql \&? 1903matches any single character. 1904A left bracket 1905.Pq Ql \&[ 1906introduces a character class. 1907The end of the character class is indicated by a 1908.Ql \&] ; 1909if the 1910.Ql \&] 1911is missing then the 1912.Ql \&[ 1913matches a 1914.Ql \&[ 1915rather than introducing a character class. 1916A character class matches any of the characters between the square brackets. 1917A locale-dependent range of characters may be specified using a minus sign. 1918A named class of characters (see 1919.Xr wctype 3 ) 1920may be specified by surrounding the name with 1921.Ql \&[:\& 1922and 1923.Ql :\&] . 1924For example, 1925.Ql \&[\&[:alpha:\&]\&] 1926is a shell pattern that matches a single letter. 1927The character class may be complemented by making an exclamation point 1928.Pq Ql !\& 1929the first character of the character class. 1930A caret 1931.Pq Ql ^ 1932has the same effect but is non-standard. 1933.Pp 1934To include a 1935.Ql \&] 1936in a character class, make it the first character listed 1937(after the 1938.Ql \&! 1939or 1940.Ql ^ , 1941if any). 1942To include a 1943.Ql - , 1944make it the first or last character listed. 1945.Ss Built-in Commands 1946This section lists the built-in commands. 1947.Bl -tag -width indent 1948.It Ic \&: 1949A null command that returns a 0 (true) exit value. 1950.It Ic \&. Ar file 1951The commands in the specified file are read and executed by the shell. 1952The 1953.Ic return 1954command may be used to return to the 1955.Ic \&. 1956command's caller. 1957If 1958.Ar file 1959contains any 1960.Ql / 1961characters, it is used as is. 1962Otherwise, the shell searches the 1963.Va PATH 1964for the file. 1965If it is not found in the 1966.Va PATH , 1967it is sought in the current working directory. 1968.It Ic \&[ 1969A built-in equivalent of 1970.Xr test 1 . 1971.It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc 1972If 1973.Ar name Ns = Ns Ar string 1974is specified, the shell defines the alias 1975.Ar name 1976with value 1977.Ar string . 1978If just 1979.Ar name 1980is specified, the value of the alias 1981.Ar name 1982is printed. 1983With no arguments, the 1984.Ic alias 1985built-in command prints the names and values of all defined aliases 1986(see 1987.Ic unalias ) . 1988Alias values are written with appropriate quoting so that they are 1989suitable for re-input to the shell. 1990Also see the 1991.Sx Aliases 1992subsection. 1993.It Ic bg Op Ar job ... 1994Continue the specified jobs 1995(or the current job if no jobs are given) 1996in the background. 1997.It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc 1998List or alter key bindings for the line editor. 1999This command is documented in 2000.Xr editrc 5 . 2001.It Ic break Op Ar num 2002See the 2003.Sx Flow-Control Constructs 2004subsection. 2005.It Ic builtin Ar cmd Op Ar arg ... 2006Execute the specified built-in command, 2007.Ar cmd . 2008This is useful when the user wishes to override a shell function 2009with the same name as a built-in command. 2010.It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory 2011.It Ic cd Fl 2012Switch to the specified 2013.Ar directory , 2014to the directory specified in the 2015.Va HOME 2016environment variable if no 2017.Ar directory 2018is specified or 2019to the directory specified in the 2020.Va OLDPWD 2021environment variable if 2022.Ar directory 2023is 2024.Fl . 2025If 2026.Ar directory 2027does not begin with 2028.Pa / , \&. , 2029or 2030.Pa .. , 2031then the directories listed in the 2032.Va CDPATH 2033variable will be 2034searched for the specified 2035.Ar directory . 2036If 2037.Va CDPATH 2038is unset, the current directory is searched. 2039The format of 2040.Va CDPATH 2041is the same as that of 2042.Va PATH . 2043In an interactive shell, 2044the 2045.Ic cd 2046command will print out the name of the directory 2047that it actually switched to 2048if the 2049.Va CDPATH 2050mechanism was used or if 2051.Ar directory 2052was 2053.Fl . 2054.Pp 2055If the 2056.Fl P 2057option is specified, 2058.Pa .. 2059is handled physically and symbolic links are resolved before 2060.Pa .. 2061components are processed. 2062If the 2063.Fl L 2064option is specified, 2065.Pa .. 2066is handled logically. 2067This is the default. 2068.Pp 2069The 2070.Fl e 2071option causes 2072.Ic cd 2073to return exit status 1 if the full pathname of the new directory 2074cannot be determined reliably or at all. 2075Normally this is not considered an error, 2076although a warning is printed. 2077.Pp 2078If changing the directory fails, the exit status is greater than 1. 2079If the directory is changed, the exit status is 0, or also 1 if 2080.Fl e 2081was given. 2082.It Ic chdir 2083A synonym for the 2084.Ic cd 2085built-in command. 2086.It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ... 2087.It Ic command Oo Fl p Oc Fl v Ar utility 2088.It Ic command Oo Fl p Oc Fl V Ar utility 2089The first form of invocation executes the specified 2090.Ar utility , 2091ignoring shell functions in the search. 2092If 2093.Ar utility 2094is a special builtin, 2095it is executed as if it were a regular builtin. 2096.Pp 2097If the 2098.Fl p 2099option is specified, the command search is performed using a 2100default value of 2101.Va PATH 2102that is guaranteed to find all of the standard utilities. 2103.Pp 2104If the 2105.Fl v 2106option is specified, 2107.Ar utility 2108is not executed but a description of its interpretation by the shell is 2109printed. 2110For ordinary commands the output is the path name; for shell built-in 2111commands, shell functions and keywords only the name is written. 2112Aliases are printed as 2113.Dq Ic alias Ar name Ns = Ns Ar value . 2114.Pp 2115The 2116.Fl V 2117option is identical to 2118.Fl v 2119except for the output. 2120It prints 2121.Dq Ar utility Ic is Ar description 2122where 2123.Ar description 2124is either 2125the path name to 2126.Ar utility , 2127a special shell builtin, 2128a shell builtin, 2129a shell function, 2130a shell keyword 2131or 2132an alias for 2133.Ar value . 2134.It Ic continue Op Ar num 2135See the 2136.Sx Flow-Control Constructs 2137subsection. 2138.It Ic echo Oo Fl e | n Oc Op Ar string ... 2139Print a space-separated list of the arguments to the standard output 2140and append a newline character. 2141.Bl -tag -width indent 2142.It Fl n 2143Suppress the output of the trailing newline. 2144.It Fl e 2145Process C-style backslash escape sequences. 2146The 2147.Ic echo 2148command understands the following character escapes: 2149.Bl -tag -width indent 2150.It \ea 2151Alert (ring the terminal bell) 2152.It \eb 2153Backspace 2154.It \ec 2155Suppress the trailing newline (this has the side-effect of truncating the 2156line if it is not the last character) 2157.It \ee 2158The ESC character (ASCII 0x1b) 2159.It \ef 2160Formfeed 2161.It \en 2162Newline 2163.It \er 2164Carriage return 2165.It \et 2166Horizontal tab 2167.It \ev 2168Vertical tab 2169.It \e\e 2170Literal backslash 2171.It \e0nnn 2172(Zero) The character whose octal value is 2173.Ar nnn 2174.El 2175.Pp 2176If 2177.Ar string 2178is not enclosed in quotes then the backslash itself must be escaped 2179with a backslash to protect it from the shell. 2180For example 2181.Bd -literal -offset indent 2182$ echo -e "a\evb" 2183a 2184 b 2185$ echo -e a\e\evb 2186a 2187 b 2188$ echo -e "a\e\eb" 2189a\eb 2190$ echo -e a\e\e\e\eb 2191a\eb 2192.Ed 2193.El 2194.Pp 2195Only one of the 2196.Fl e 2197and 2198.Fl n 2199options may be specified. 2200.It Ic eval Ar string ... 2201Concatenate all the arguments with spaces. 2202Then re-parse and execute the command. 2203.It Ic exec Op Ar command Op arg ... 2204Unless 2205.Ar command 2206is omitted, 2207the shell process is replaced with the specified program 2208(which must be a real program, not a shell built-in command or function). 2209Any redirections on the 2210.Ic exec 2211command are marked as permanent, 2212so that they are not undone when the 2213.Ic exec 2214command finishes. 2215.It Ic exit Op Ar exitstatus 2216Terminate the shell process. 2217If 2218.Ar exitstatus 2219is given 2220it is used as the exit status of the shell. 2221Otherwise, if the shell is executing an 2222.Cm EXIT 2223trap, the exit status of the last command before the trap is used; 2224if the shell is executing a trap for a signal, 2225the shell exits by resending the signal to itself. 2226Otherwise, the exit status of the preceding command is used. 2227The exit status should be an integer between 0 and 255. 2228.It Ic export Ar name ... 2229.It Ic export Op Fl p 2230The specified names are exported so that they will 2231appear in the environment of subsequent commands. 2232The only way to un-export a variable is to 2233.Ic unset 2234it. 2235The shell allows the value of a variable to be set 2236at the same time as it is exported by writing 2237.Pp 2238.D1 Ic export Ar name Ns = Ns Ar value 2239.Pp 2240With no arguments the 2241.Ic export 2242command lists the names 2243of all exported variables. 2244If the 2245.Fl p 2246option is specified, the exported variables are printed as 2247.Dq Ic export Ar name Ns = Ns Ar value 2248lines, suitable for re-input to the shell. 2249.It Ic false 2250A null command that returns a non-zero (false) exit value. 2251.It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last 2252.It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last 2253.It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first 2254The 2255.Ic fc 2256built-in command lists, or edits and re-executes, 2257commands previously entered to an interactive shell. 2258.Bl -tag -width indent 2259.It Fl e Ar editor 2260Use the editor named by 2261.Ar editor 2262to edit the commands. 2263The 2264.Ar editor 2265string is a command name, 2266subject to search via the 2267.Va PATH 2268variable. 2269The value in the 2270.Va FCEDIT 2271variable is used as a default when 2272.Fl e 2273is not specified. 2274If 2275.Va FCEDIT 2276is null or unset, the value of the 2277.Va EDITOR 2278variable is used. 2279If 2280.Va EDITOR 2281is null or unset, 2282.Xr ed 1 2283is used as the editor. 2284.It Fl l No (ell) 2285List the commands rather than invoking 2286an editor on them. 2287The commands are written in the 2288sequence indicated by the 2289.Ar first 2290and 2291.Ar last 2292operands, as affected by 2293.Fl r , 2294with each command preceded by the command number. 2295.It Fl n 2296Suppress command numbers when listing with 2297.Fl l . 2298.It Fl r 2299Reverse the order of the commands listed 2300(with 2301.Fl l ) 2302or edited 2303(with neither 2304.Fl l 2305nor 2306.Fl s ) . 2307.It Fl s 2308Re-execute the command without invoking an editor. 2309.It Ar first 2310.It Ar last 2311Select the commands to list or edit. 2312The number of previous commands that can be accessed 2313are determined by the value of the 2314.Va HISTSIZE 2315variable. 2316The value of 2317.Ar first 2318or 2319.Ar last 2320or both are one of the following: 2321.Bl -tag -width indent 2322.It Oo Cm + Oc Ns Ar num 2323A positive number representing a command number; 2324command numbers can be displayed with the 2325.Fl l 2326option. 2327.It Fl Ar num 2328A negative decimal number representing the 2329command that was executed 2330.Ar num 2331of 2332commands previously. 2333For example, \-1 is the immediately previous command. 2334.It Ar string 2335A string indicating the most recently entered command 2336that begins with that string. 2337If the 2338.Ar old Ns = Ns Ar new 2339operand is not also specified with 2340.Fl s , 2341the string form of the first operand cannot contain an embedded equal sign. 2342.El 2343.El 2344.Pp 2345The following variables affect the execution of 2346.Ic fc : 2347.Bl -tag -width ".Va HISTSIZE" 2348.It Va FCEDIT 2349Name of the editor to use for history editing. 2350.It Va HISTSIZE 2351The number of previous commands that are accessible. 2352.El 2353.It Ic fg Op Ar job 2354Move the specified 2355.Ar job 2356or the current job to the foreground. 2357.It Ic getopts Ar optstring var 2358The POSIX 2359.Ic getopts 2360command. 2361The 2362.Ic getopts 2363command deprecates the older 2364.Xr getopt 1 2365command. 2366The first argument should be a series of letters, each possibly 2367followed by a colon which indicates that the option takes an argument. 2368The specified variable is set to the parsed option. 2369The index of 2370the next argument is placed into the shell variable 2371.Va OPTIND . 2372If an option takes an argument, it is placed into the shell variable 2373.Va OPTARG . 2374If an invalid option is encountered, 2375.Ar var 2376is set to 2377.Ql \&? . 2378It returns a false value (1) when it encounters the end of the options. 2379A new set of arguments may be parsed by assigning 2380.Li OPTIND=1 . 2381.It Ic hash Oo Fl rv Oc Op Ar command ... 2382The shell maintains a hash table which remembers the locations of commands. 2383With no arguments whatsoever, the 2384.Ic hash 2385command prints out the contents of this table. 2386.Pp 2387With arguments, the 2388.Ic hash 2389command removes each specified 2390.Ar command 2391from the hash table (unless they are functions) and then locates it. 2392With the 2393.Fl v 2394option, 2395.Ic hash 2396prints the locations of the commands as it finds them. 2397The 2398.Fl r 2399option causes the 2400.Ic hash 2401command to delete all the entries in the hash table except for functions. 2402.It Ic jobid Op Ar job 2403Print the process IDs of the processes in the specified 2404.Ar job . 2405If the 2406.Ar job 2407argument is omitted, use the current job. 2408.It Ic jobs Oo Fl lps Oc Op Ar job ... 2409Print information about the specified jobs, or all jobs if no 2410.Ar job 2411argument is given. 2412The information printed includes job ID, status and command name. 2413.Pp 2414If the 2415.Fl l 2416option is specified, the PID of each job is also printed. 2417If the 2418.Fl p 2419option is specified, only the process IDs for the process group leaders 2420are printed, one per line. 2421If the 2422.Fl s 2423option is specified, only the PIDs of the job commands are printed, one per 2424line. 2425.It Ic kill 2426A built-in equivalent of 2427.Xr kill 1 2428that additionally supports sending signals to jobs. 2429.It Ic local Oo Ar variable ... Oc Op Fl 2430See the 2431.Sx Functions 2432subsection. 2433.It Ic printf 2434A built-in equivalent of 2435.Xr printf 1 . 2436.It Ic pwd Op Fl L | P 2437Print the path of the current directory. 2438The built-in command may 2439differ from the program of the same name because the 2440built-in command remembers what the current directory 2441is rather than recomputing it each time. 2442This makes 2443it faster. 2444However, if the current directory is 2445renamed, 2446the built-in version of 2447.Xr pwd 1 2448will continue to print the old name for the directory. 2449.Pp 2450If the 2451.Fl P 2452option is specified, symbolic links are resolved. 2453If the 2454.Fl L 2455option is specified, the shell's notion of the current directory 2456is printed (symbolic links are not resolved). 2457This is the default. 2458.It Ic read Oo Fl p Ar prompt Oc Oo 2459.Fl t Ar timeout Oc Oo Fl er Oc Ar variable ... 2460The 2461.Ar prompt 2462is printed if the 2463.Fl p 2464option is specified 2465and the standard input is a terminal. 2466Then a line is 2467read from the standard input. 2468The trailing newline 2469is deleted from the line and the line is split as 2470described in the section on 2471.Sx White Space Splitting (Field Splitting)\& 2472above, and 2473the pieces are assigned to the variables in order. 2474If there are more pieces than variables, the remaining 2475pieces (along with the characters in 2476.Va IFS 2477that separated them) 2478are assigned to the last variable. 2479If there are more variables than pieces, the remaining 2480variables are assigned the null string. 2481.Pp 2482Backslashes are treated specially, unless the 2483.Fl r 2484option is 2485specified. 2486If a backslash is followed by 2487a newline, the backslash and the newline will be 2488deleted. 2489If a backslash is followed by any other 2490character, the backslash will be deleted and the following 2491character will be treated as though it were not in 2492.Va IFS , 2493even if it is. 2494.Pp 2495If the 2496.Fl t 2497option is specified and the 2498.Ar timeout 2499elapses before a complete line of input is supplied, 2500the 2501.Ic read 2502command will return an exit status as if terminated by 2503.Dv SIGALRM 2504without assigning any values. 2505The 2506.Ar timeout 2507value may optionally be followed by one of 2508.Ql s , 2509.Ql m 2510or 2511.Ql h 2512to explicitly specify seconds, minutes or hours. 2513If none is supplied, 2514.Ql s 2515is assumed. 2516.Pp 2517The 2518.Fl e 2519option exists only for backward compatibility with older scripts. 2520.Pp 2521The exit status is 0 on success, 1 on end of file, 2522between 2 and 128 if an error occurs 2523and greater than 128 if a trapped signal interrupts 2524.Ic read . 2525.It Ic readonly Oo Fl p Oc Op Ar name ... 2526Each specified 2527.Ar name 2528is marked as read only, 2529so that it cannot be subsequently modified or unset. 2530The shell allows the value of a variable to be set 2531at the same time as it is marked read only 2532by using the following form: 2533.Pp 2534.D1 Ic readonly Ar name Ns = Ns Ar value 2535.Pp 2536With no arguments the 2537.Ic readonly 2538command lists the names of all read only variables. 2539If the 2540.Fl p 2541option is specified, the read-only variables are printed as 2542.Dq Ic readonly Ar name Ns = Ns Ar value 2543lines, suitable for re-input to the shell. 2544.It Ic return Op Ar exitstatus 2545See the 2546.Sx Functions 2547subsection. 2548.It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname 2549.Oc Op Fl - Ar arg ... 2550The 2551.Ic set 2552command performs three different functions: 2553.Bl -item 2554.It 2555With no arguments, it lists the values of all shell variables. 2556.It 2557If options are given, 2558either in short form or using the long 2559.Dq Fl /+o Ar longname 2560form, 2561it sets or clears the specified options as described in the section called 2562.Sx Argument List Processing . 2563.It 2564If the 2565.Dq Fl - 2566option is specified, 2567.Ic set 2568will replace the shell's positional parameters with the subsequent 2569arguments. 2570If no arguments follow the 2571.Dq Fl - 2572option, 2573all the positional parameters will be cleared, 2574which is equivalent to executing the command 2575.Dq Li "shift $#" . 2576The 2577.Dq Fl - 2578flag may be omitted when specifying arguments to be used 2579as positional replacement parameters. 2580This is not recommended, 2581because the first argument may begin with a dash 2582.Pq Ql - 2583or a plus 2584.Pq Ql + , 2585which the 2586.Ic set 2587command will interpret as a request to enable or disable options. 2588.El 2589.It Ic setvar Ar variable value 2590Assigns the specified 2591.Ar value 2592to the specified 2593.Ar variable . 2594The 2595.Ic setvar 2596command is intended to be used in functions that 2597assign values to variables whose names are passed as parameters. 2598In general it is better to write 2599.Dq Ar variable Ns = Ns Ar value 2600rather than using 2601.Ic setvar . 2602.It Ic shift Op Ar n 2603Shift the positional parameters 2604.Ar n 2605times, or once if 2606.Ar n 2607is not specified. 2608A shift sets the value of 2609.Li $1 2610to the value of 2611.Li $2 , 2612the value of 2613.Li $2 2614to the value of 2615.Li $3 , 2616and so on, 2617decreasing the value of 2618.Li $# 2619by one. 2620For portability, shifting if there are zero positional parameters 2621should be avoided, since the shell may abort. 2622.It Ic test 2623A built-in equivalent of 2624.Xr test 1 . 2625.It Ic times 2626Print the amount of time spent executing the shell process and its children. 2627The first output line shows the user and system times for the shell process 2628itself, the second one contains the user and system times for the 2629children. 2630.It Ic trap Oo Ar action Oc Ar signal ... 2631.It Ic trap Fl l 2632Cause the shell to parse and execute 2633.Ar action 2634when any specified 2635.Ar signal 2636is received. 2637The signals are specified by name or number. 2638In addition, the pseudo-signal 2639.Cm EXIT 2640may be used to specify an 2641.Ar action 2642that is performed when the shell terminates. 2643The 2644.Ar action 2645may be an empty string or a dash 2646.Pq Ql - ; 2647the former causes the specified signal to be ignored 2648and the latter causes the default action to be taken. 2649Omitting the 2650.Ar action 2651and using only signal numbers is another way to request the default action. 2652In a subshell or utility environment, 2653the shell resets trapped (but not ignored) signals to the default action. 2654The 2655.Ic trap 2656command has no effect on signals that were ignored on entry to the shell. 2657.Pp 2658Option 2659.Fl l 2660causes the 2661.Ic trap 2662command to display a list of valid signal names. 2663.It Ic true 2664A null command that returns a 0 (true) exit value. 2665.It Ic type Op Ar name ... 2666Interpret each 2667.Ar name 2668as a command and print the resolution of the command search. 2669Possible resolutions are: 2670shell keyword, alias, special shell builtin, shell builtin, command, 2671tracked alias 2672and not found. 2673For aliases the alias expansion is printed; 2674for commands and tracked aliases 2675the complete pathname of the command is printed. 2676.It Ic ulimit Oo Fl HSabcdfklmnopstuvw Oc Op Ar limit 2677Set or display resource limits (see 2678.Xr getrlimit 2 ) . 2679If 2680.Ar limit 2681is specified, the named resource will be set; 2682otherwise the current resource value will be displayed. 2683.Pp 2684If 2685.Fl H 2686is specified, the hard limits will be set or displayed. 2687While everybody is allowed to reduce a hard limit, 2688only the superuser can increase it. 2689The 2690.Fl S 2691option 2692specifies the soft limits instead. 2693When displaying limits, 2694only one of 2695.Fl S 2696or 2697.Fl H 2698can be given. 2699The default is to display the soft limits, 2700and to set both the hard and the soft limits. 2701.Pp 2702Option 2703.Fl a 2704causes the 2705.Ic ulimit 2706command to display all resources. 2707The parameter 2708.Ar limit 2709is not acceptable in this mode. 2710.Pp 2711The remaining options specify which resource value is to be 2712displayed or modified. 2713They are mutually exclusive. 2714.Bl -tag -width indent 2715.It Fl b Ar sbsize 2716The maximum size of socket buffer usage, in bytes. 2717.It Fl c Ar coredumpsize 2718The maximal size of core dump files, in 512-byte blocks. 2719Setting 2720.Ar coredumpsize 2721to 0 prevents core dump files from being created. 2722.It Fl d Ar datasize 2723The maximal size of the data segment of a process, in kilobytes. 2724.It Fl f Ar filesize 2725The maximal size of a file, in 512-byte blocks. 2726.It Fl k Ar kqueues 2727The maximal number of kqueues 2728(see 2729.Xr kqueue 2 ) 2730for this user ID. 2731.It Fl l Ar lockedmem 2732The maximal size of memory that can be locked by a process, in 2733kilobytes. 2734.It Fl m Ar memoryuse 2735The maximal resident set size of a process, in kilobytes. 2736.It Fl n Ar nofiles 2737The maximal number of descriptors that could be opened by a process. 2738.It Fl o Ar umtxp 2739The maximal number of process-shared locks 2740(see 2741.Xr pthread 3 ) 2742for this user ID. 2743.It Fl p Ar pseudoterminals 2744The maximal number of pseudo-terminals for this user ID. 2745.It Fl s Ar stacksize 2746The maximal size of the stack segment, in kilobytes. 2747.It Fl t Ar time 2748The maximal amount of CPU time to be used by each process, in seconds. 2749.It Fl u Ar userproc 2750The maximal number of simultaneous processes for this user ID. 2751.It Fl v Ar virtualmem 2752The maximal virtual size of a process, in kilobytes. 2753.It Fl w Ar swapuse 2754The maximum amount of swap space reserved or used for this user ID, 2755in kilobytes. 2756.El 2757.It Ic umask Oo Fl S Oc Op Ar mask 2758Set the file creation mask (see 2759.Xr umask 2 ) 2760to the octal or symbolic (see 2761.Xr chmod 1 ) 2762value specified by 2763.Ar mask . 2764If the argument is omitted, the current mask value is printed. 2765If the 2766.Fl S 2767option is specified, the output is symbolic, otherwise the output is octal. 2768.It Ic unalias Oo Fl a Oc Op Ar name ... 2769The specified alias names are removed. 2770If 2771.Fl a 2772is specified, all aliases are removed. 2773.It Ic unset Oo Fl fv Oc Ar name ... 2774The specified variables or functions are unset and unexported. 2775If the 2776.Fl v 2777option is specified or no options are given, the 2778.Ar name 2779arguments are treated as variable names. 2780If the 2781.Fl f 2782option is specified, the 2783.Ar name 2784arguments are treated as function names. 2785.It Ic wait Op Ar job ... 2786Wait for each specified 2787.Ar job 2788to complete and return the exit status of the last process in the 2789last specified 2790.Ar job . 2791If any 2792.Ar job 2793specified is unknown to the shell, it is treated as if it 2794were a known job that exited with exit status 127. 2795If no operands are given, wait for all jobs to complete 2796and return an exit status of zero. 2797.El 2798.Ss Command Line Editing 2799When 2800.Nm 2801is being used interactively from a terminal, the current command 2802and the command history 2803(see 2804.Ic fc 2805in 2806.Sx Built-in Commands ) 2807can be edited using 2808.Nm vi Ns -mode 2809command line editing. 2810This mode uses commands similar 2811to a subset of those described in the 2812.Xr vi 1 2813man page. 2814The command 2815.Dq Li "set -o vi" 2816(or 2817.Dq Li "set -V" ) 2818enables 2819.Nm vi Ns -mode 2820editing and places 2821.Nm 2822into 2823.Nm vi 2824insert mode. 2825With 2826.Nm vi Ns -mode 2827enabled, 2828.Nm 2829can be switched between insert mode and command mode by typing 2830.Aq ESC . 2831Hitting 2832.Aq return 2833while in command mode will pass the line to the shell. 2834.Pp 2835Similarly, the 2836.Dq Li "set -o emacs" 2837(or 2838.Dq Li "set -E" ) 2839command can be used to enable a subset of 2840.Nm emacs Ns -style 2841command line editing features. 2842.Sh ENVIRONMENT 2843The following environment variables affect the execution of 2844.Nm : 2845.Bl -tag -width ".Ev LANGXXXXXX" 2846.It Ev ENV 2847Initialization file for interactive shells. 2848.It Ev LANG , Ev LC_* 2849Locale settings. 2850These are inherited by children of the shell, 2851and is used in a limited manner by the shell itself. 2852.It Ev OLDPWD 2853The previous current directory. 2854This is used and updated by 2855.Ic cd . 2856.It Ev PWD 2857An absolute pathname for the current directory, 2858possibly containing symbolic links. 2859This is used and updated by the shell. 2860.It Ev TERM 2861The default terminal setting for the shell. 2862This is inherited by children of the shell, and is used in the history 2863editing modes. 2864.El 2865.Pp 2866Additionally, environment variables are turned into shell variables 2867at startup, 2868which may affect the shell as described under 2869.Sx Special Variables . 2870.Sh FILES 2871.Bl -tag -width "/etc/suid_profileXX" -compact 2872.It Pa ~/.profile 2873User's login profile. 2874.It Pa /etc/profile 2875System login profile. 2876.It Pa /etc/shells 2877Shell database. 2878.It Pa /etc/suid_profile 2879Privileged shell profile. 2880.El 2881.Sh EXIT STATUS 2882If the 2883.Ar script 2884cannot be found, the exit status will be 127; 2885if it cannot be opened for another reason, the exit status will be 126. 2886Other errors that are detected by the shell, such as a syntax error, will 2887cause the shell to exit with a non-zero exit status. 2888If the shell is not an interactive shell, the execution of the shell 2889file will be aborted. 2890Otherwise the shell will return the exit status of the last command 2891executed, or if the 2892.Ic exit 2893builtin is used with a numeric argument, it 2894will return the argument. 2895.Sh SEE ALSO 2896.Xr builtin 1 , 2897.Xr chsh 1 , 2898.Xr echo 1 , 2899.Xr ed 1 , 2900.Xr emacs 1 Pq Pa ports/editors/emacs , 2901.Xr kill 1 , 2902.Xr printf 1 , 2903.Xr pwd 1 , 2904.Xr test 1 , 2905.Xr vi 1 , 2906.Xr execve 2 , 2907.Xr getrlimit 2 , 2908.Xr umask 2 , 2909.Xr wctype 3 , 2910.Xr editrc 5 , 2911.Xr shells 5 2912.Sh HISTORY 2913A 2914.Nm 2915command, the Thompson shell, appeared in 2916.At v1 . 2917It was superseded in 2918.At v7 2919by the Bourne shell, which inherited the name 2920.Nm . 2921.Pp 2922This version of 2923.Nm 2924was rewritten in 1989 under the 2925.Bx 2926license after the Bourne shell from 2927.At V.4 2928and first appeared in 2929.Bx 4.3 Net/2 . 2930.Sh AUTHORS 2931This version of 2932.Nm 2933was originally written by 2934.An Kenneth Almquist . 2935.Sh BUGS 2936The 2937.Nm 2938utility does not recognize multibyte characters other than UTF-8. 2939Splitting using 2940.Va IFS 2941does not recognize multibyte characters. 2942