1.\"- 2.\" Copyright (c) 1991, 1993 3.\" The Regents of the University of California. All rights reserved. 4.\" 5.\" This code is derived from software contributed to Berkeley by 6.\" Kenneth Almquist. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 3. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" from: @(#)sh.1 8.6 (Berkeley) 5/4/95 33.\" $FreeBSD$ 34.\" 35.Dd May 10, 2021 36.Dt SH 1 37.Os 38.Sh NAME 39.Nm sh 40.Nd command interpreter (shell) 41.Sh SYNOPSIS 42.Nm 43.Op Fl /+abCEefhIimnPpTuVvx 44.Op Fl /+o Ar longname 45.Oo 46.Ar script 47.Op Ar arg ... 48.Oc 49.Nm 50.Op Fl /+abCEefhIimnPpTuVvx 51.Op Fl /+o Ar longname 52.Fl c Ar string 53.Oo 54.Ar name 55.Op Ar arg ... 56.Oc 57.Nm 58.Op Fl /+abCEefhIimnPpTuVvx 59.Op Fl /+o Ar longname 60.Fl s 61.Op Ar arg ... 62.Sh DESCRIPTION 63The 64.Nm 65utility is the standard command interpreter for the system. 66The current version of 67.Nm 68is close to the 69.St -p1003.1 70specification for the shell. 71It only supports features 72designated by POSIX, 73plus a few Berkeley extensions. 74This man page is not intended to be a tutorial nor a complete 75specification of the shell. 76.Ss Overview 77The shell is a command that reads lines from 78either a file or the terminal, interprets them, and 79generally executes other commands. 80It is the program that is started when a user logs into the system, 81although a user can select a different shell with the 82.Xr chsh 1 83command. 84The shell 85implements a language that has flow control constructs, 86a macro facility that provides a variety of features in 87addition to data storage, along with built-in history and line 88editing capabilities. 89It incorporates many features to 90aid interactive use and has the advantage that the interpretative 91language is common to both interactive and non-interactive 92use (shell scripts). 93That is, commands can be typed directly 94to the running shell or can be put into a file, 95which can be executed directly by the shell. 96.Ss Invocation 97.\" 98.\" XXX This next sentence is incredibly confusing. 99.\" 100If no arguments are present and if the standard input of the shell 101is connected to a terminal 102(or if the 103.Fl i 104option is set), 105the shell is considered an interactive shell. 106An interactive shell 107generally prompts before each command and handles programming 108and command errors differently (as described below). 109When first starting, the shell inspects argument 0, and 110if it begins with a dash 111.Pq Ql - , 112the shell is also considered a login shell. 113This is normally done automatically by the system 114when the user first logs in. 115A login shell first reads commands 116from the files 117.Pa /etc/profile 118and then 119.Pa .profile 120in a user's home directory, 121if they exist. 122If the environment variable 123.Ev ENV 124is set on entry to a shell, or is set in the 125.Pa .profile 126of a login shell, the shell then subjects its value to parameter expansion 127and arithmetic expansion and reads commands from the named file. 128Therefore, a user should place commands that are to be executed only 129at login time in the 130.Pa .profile 131file, and commands that are executed for every shell inside the 132.Ev ENV 133file. 134The user can set the 135.Ev ENV 136variable to some file by placing the following line in the file 137.Pa .profile 138in the home directory, 139substituting for 140.Pa .shrc 141the filename desired: 142.Pp 143.Dl "ENV=$HOME/.shrc; export ENV" 144.Pp 145The first non-option argument specified on the command line 146will be treated as the 147name of a file from which to read commands (a shell script), and 148the remaining arguments are set as the positional parameters 149of the shell 150.Li ( $1 , $2 , 151etc.). 152Otherwise, the shell reads commands 153from its standard input. 154.Pp 155Unlike older versions of 156.Nm 157the 158.Ev ENV 159script is only sourced on invocation of interactive shells. 160This 161closes a well-known, and sometimes easily exploitable security 162hole related to poorly thought out 163.Ev ENV 164scripts. 165.Ss Argument List Processing 166All of the single letter options to 167.Nm 168have a corresponding long name, 169with the exception of 170.Fl c 171and 172.Fl /+o . 173These long names are provided next to the single letter options 174in the descriptions below. 175The long name for an option may be specified as an argument to the 176.Fl /+o 177option of 178.Nm . 179Once the shell is running, 180the long name for an option may be specified as an argument to the 181.Fl /+o 182option of the 183.Ic set 184built-in command 185(described later in the section called 186.Sx Built-in Commands ) . 187Introducing an option with a dash 188.Pq Ql - 189enables the option, 190while using a plus 191.Pq Ql + 192disables the option. 193A 194.Dq Li -- 195or plain 196.Ql - 197will stop option processing and will force the remaining 198words on the command line to be treated as arguments. 199The 200.Fl /+o 201and 202.Fl c 203options do not have long names. 204They take arguments and are described after the single letter options. 205.Bl -tag -width indent 206.It Fl a Li allexport 207Flag variables for export when assignments are made to them. 208.It Fl b Li notify 209Enable asynchronous notification of background job 210completion. 211(UNIMPLEMENTED) 212.It Fl C Li noclobber 213Do not overwrite existing files with 214.Ql > . 215.It Fl E Li emacs 216Enable the built-in 217.Xr emacs 1 218command line editor (disables the 219.Fl V 220option if it has been set; 221set automatically when interactive on terminals). 222.It Fl e Li errexit 223Exit immediately if any untested command fails in non-interactive mode. 224The exit status of a command is considered to be 225explicitly tested if the command is part of the list used to control 226an 227.Ic if , elif , while , 228or 229.Ic until ; 230if the command is the left 231hand operand of an 232.Dq Li && 233or 234.Dq Li || 235operator; or if the command is a pipeline preceded by the 236.Ic !\& 237keyword. 238If a shell function is executed and its exit status is explicitly 239tested, all commands of the function are considered to be tested as 240well. 241.Pp 242It is recommended to check for failures explicitly 243instead of relying on 244.Fl e 245because it tends to behave in unexpected ways, 246particularly in larger scripts. 247.It Fl f Li noglob 248Disable pathname expansion. 249.It Fl h Li trackall 250A do-nothing option for POSIX compliance. 251.It Fl I Li ignoreeof 252Ignore 253.Dv EOF Ap s 254from input when in interactive mode. 255.It Fl i Li interactive 256Force the shell to behave interactively. 257.It Fl m Li monitor 258Turn on job control (set automatically when interactive). 259A new process group is created for each pipeline (called a job). 260It is possible to suspend jobs or to have them run in the foreground or 261in the background. 262In a non-interactive shell, 263this option can be set even if no terminal is available 264and is useful to place processes in separate process groups. 265.It Fl n Li noexec 266If not interactive, read commands but do not 267execute them. 268This is useful for checking the 269syntax of shell scripts. 270.It Fl P Li physical 271Change the default for the 272.Ic cd 273and 274.Ic pwd 275commands from 276.Fl L 277(logical directory layout) 278to 279.Fl P 280(physical directory layout). 281.It Fl p Li privileged 282Turn on privileged mode. 283This mode is enabled on startup 284if either the effective user or group ID is not equal to the 285real user or group ID. 286Turning this mode off sets the 287effective user and group IDs to the real user and group IDs. 288When this mode is enabled for interactive shells, the file 289.Pa /etc/suid_profile 290is sourced instead of 291.Pa ~/.profile 292after 293.Pa /etc/profile 294is sourced, and the contents of the 295.Ev ENV 296variable are ignored. 297.It Fl s Li stdin 298Read commands from standard input (set automatically 299if no file arguments are present). 300This option has 301no effect when set after the shell has already started 302running (i.e., when set with the 303.Ic set 304command). 305.It Fl T Li trapsasync 306When waiting for a child, execute traps immediately. 307If this option is not set, 308traps are executed after the child exits, 309as specified in 310.St -p1003.2 . 311This nonstandard option is useful for putting guarding shells around 312children that block signals. 313The surrounding shell may kill the child 314or it may just return control to the tty and leave the child alone, 315like this: 316.Bd -literal -offset indent 317sh -T -c "trap 'exit 1' 2 ; some-blocking-program" 318.Ed 319.It Fl u Li nounset 320Write a message to standard error when attempting 321to expand a variable, a positional parameter or 322the special parameter 323.Va \&! 324that is not set, and if the 325shell is not interactive, exit immediately. 326.It Fl V Li vi 327Enable the built-in 328.Xr vi 1 329command line editor (disables 330.Fl E 331if it has been set). 332.It Fl v Li verbose 333The shell writes its input to standard error 334as it is read. 335Useful for debugging. 336.It Fl x Li xtrace 337Write each command 338(preceded by the value of the 339.Va PS4 340variable subjected to parameter expansion and arithmetic expansion) 341to standard error before it is executed. 342Useful for debugging. 343.It Li nolog 344Another do-nothing option for POSIX compliance. 345It only has a long name. 346.It Li pipefail 347Change the exit status of a pipeline to the last non-zero exit status of 348any command in the pipeline, if any. 349Since an exit due to 350.Dv SIGPIPE 351counts as a non-zero exit status, 352this option may cause non-zero exit status for successful pipelines 353if a command such as 354.Xr head 1 355in the pipeline terminates with status 0 without reading its 356input completely. 357This option only has a long name. 358.El 359.Pp 360The 361.Fl c 362option causes the commands to be read from the 363.Ar string 364operand instead of from the standard input. 365Keep in mind that this option only accepts a single string as its 366argument, hence multi-word strings must be quoted. 367.Pp 368The 369.Fl /+o 370option takes as its only argument the long name of an option 371to be enabled or disabled. 372For example, the following two invocations of 373.Nm 374both enable the built-in 375.Xr emacs 1 376command line editor: 377.Bd -literal -offset indent 378set -E 379set -o emacs 380.Ed 381.Pp 382If used without an argument, the 383.Fl o 384option displays the current option settings in a human-readable format. 385If 386.Cm +o 387is used without an argument, the current option settings are output 388in a format suitable for re-input into the shell. 389.Ss Lexical Structure 390The shell reads input in terms of lines from a file and breaks 391it up into words at whitespace (blanks and tabs), and at 392certain sequences of 393characters called 394.Dq operators , 395which are special to the shell. 396There are two types of operators: control operators and 397redirection operators (their meaning is discussed later). 398The following is a list of valid operators: 399.Bl -tag -width indent 400.It Control operators: 401.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 402.It Li & Ta Li && Ta Li \&( Ta Li \&) Ta Li \en 403.It Li ;; Ta Li ;& Ta Li \&; Ta Li \&| Ta Li || 404.El 405.It Redirection operators: 406.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 407.It Li < Ta Li > Ta Li << Ta Li >> Ta Li <> 408.It Li <& Ta Li >& Ta Li <<- Ta Li >| Ta \& 409.El 410.El 411.Pp 412The character 413.Ql # 414introduces a comment if used at the beginning of a word. 415The word starting with 416.Ql # 417and the rest of the line are ignored. 418.Pp 419ASCII 420.Dv NUL 421characters (character code 0) are not allowed in shell input. 422.Ss Quoting 423Quoting is used to remove the special meaning of certain characters 424or words to the shell, such as operators, whitespace, keywords, 425or alias names. 426.Pp 427There are four types of quoting: matched single quotes, 428dollar-single quotes, 429matched double quotes, and backslash. 430.Bl -tag -width indent 431.It Single Quotes 432Enclosing characters in single quotes preserves the literal 433meaning of all the characters (except single quotes, making 434it impossible to put single-quotes in a single-quoted string). 435.It Dollar-Single Quotes 436Enclosing characters between 437.Li $' 438and 439.Li ' 440preserves the literal meaning of all characters 441except backslashes and single quotes. 442A backslash introduces a C-style escape sequence: 443.Bl -tag -width xUnnnnnnnn 444.It \ea 445Alert (ring the terminal bell) 446.It \eb 447Backspace 448.It \ec Ns Ar c 449The control character denoted by 450.Li ^ Ns Ar c 451in 452.Xr stty 1 . 453If 454.Ar c 455is a backslash, it must be doubled. 456.It \ee 457The ESC character (ASCII 0x1b) 458.It \ef 459Formfeed 460.It \en 461Newline 462.It \er 463Carriage return 464.It \et 465Horizontal tab 466.It \ev 467Vertical tab 468.It \e\e 469Literal backslash 470.It \e\&' 471Literal single-quote 472.It \e\&" 473Literal double-quote 474.It \e Ns Ar nnn 475The byte whose octal value is 476.Ar nnn 477(one to three digits) 478.It \ex Ns Ar nn 479The byte whose hexadecimal value is 480.Ar nn 481(one or more digits only the last two of which are used) 482.It \eu Ns Ar nnnn 483The Unicode code point 484.Ar nnnn 485(four hexadecimal digits) 486.It \eU Ns Ar nnnnnnnn 487The Unicode code point 488.Ar nnnnnnnn 489(eight hexadecimal digits) 490.El 491.Pp 492The sequences for Unicode code points are currently only useful with 493UTF-8 locales. 494They reject code point 0 and UTF-16 surrogates. 495.Pp 496If an escape sequence would produce a byte with value 0, 497that byte and the rest of the string until the matching single-quote 498are ignored. 499.Pp 500Any other string starting with a backslash is an error. 501.It Double Quotes 502Enclosing characters within double quotes preserves the literal 503meaning of all characters except dollar sign 504.Pq Ql $ , 505backquote 506.Pq Ql ` , 507and backslash 508.Pq Ql \e . 509The backslash inside double quotes is historically weird. 510It remains literal unless it precedes the following characters, 511which it serves to quote: 512.Pp 513.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact 514.It Li $ Ta Li ` Ta Li \&" Ta Li \e Ta Li \en 515.El 516.It Backslash 517A backslash preserves the literal meaning of the following 518character, with the exception of the newline character 519.Pq Ql \en . 520A backslash preceding a newline is treated as a line continuation. 521.El 522.Ss Keywords 523Keywords or reserved words are words that have special meaning to the 524shell and are recognized at the beginning of a line and 525after a control operator. 526The following are keywords: 527.Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center 528.It Li \&! Ta { Ta } Ta Ic case Ta Ic do 529.It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi 530.It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while 531.El 532.Ss Aliases 533An alias is a name and corresponding value set using the 534.Ic alias 535built-in command. 536Wherever the command word of a simple command may occur, 537and after checking for keywords if a keyword may occur, the shell 538checks the word to see if it matches an alias. 539If it does, it replaces it in the input stream with its value. 540For example, if there is an alias called 541.Dq Li lf 542with the value 543.Dq Li "ls -F" , 544then the input 545.Pp 546.Dl "lf foobar" 547.Pp 548would become 549.Pp 550.Dl "ls -F foobar" 551.Pp 552Aliases are also recognized after an alias 553whose value ends with a space or tab. 554For example, if there is also an alias called 555.Dq Li nohup 556with the value 557.Dq Li "nohup " , 558then the input 559.Pp 560.Dl "nohup lf foobar" 561.Pp 562would become 563.Pp 564.Dl "nohup ls -F foobar" 565.Pp 566Aliases provide a convenient way for naive users to 567create shorthands for commands without having to learn how 568to create functions with arguments. 569Using aliases in scripts is discouraged 570because the command that defines them must be executed 571before the code that uses them is parsed. 572This is fragile and not portable. 573.Pp 574An alias name may be escaped in a command line, so that it is not 575replaced by its alias value, by using quoting characters within or 576adjacent to the alias name. 577This is most often done by prefixing 578an alias name with a backslash to execute a function, built-in, or 579normal program with the same name. 580See the 581.Sx Quoting 582subsection. 583.Ss Commands 584The shell interprets the words it reads according to a 585language, the specification of which is outside the scope 586of this man page (refer to the BNF in the 587.St -p1003.2 588document). 589Essentially though, a line is read and if 590the first word of the line (or after a control operator) 591is not a keyword, then the shell has recognized a 592simple command. 593Otherwise, a complex command or some 594other special construct may have been recognized. 595.Ss Simple Commands 596If a simple command has been recognized, the shell performs 597the following actions: 598.Bl -enum 599.It 600Leading words of the form 601.Dq Li name=value 602are stripped off and assigned to the environment of 603the simple command 604(they do not affect expansions). 605Redirection operators and 606their arguments (as described below) are stripped 607off and saved for processing. 608.It 609The remaining words are expanded as described in 610the section called 611.Sx Word Expansions , 612and the first remaining word is considered the command 613name and the command is located. 614The remaining 615words are considered the arguments of the command. 616If no command name resulted, then the 617.Dq Li name=value 618variable assignments recognized in 1) affect the 619current shell. 620.It 621Redirections are performed as described in 622the next section. 623.El 624.Ss Redirections 625Redirections are used to change where a command reads its input 626or sends its output. 627In general, redirections open, close, or 628duplicate an existing reference to a file. 629The overall format 630used for redirection is: 631.Pp 632.D1 Oo Ar n Oc Ar redir-op file 633.Pp 634The 635.Ar redir-op 636is one of the redirection operators mentioned 637previously. 638The following gives some examples of how these 639operators can be used. 640Note that stdin and stdout are commonly used abbreviations 641for standard input and standard output respectively. 642.Bl -tag -width "1234567890XX" -offset indent 643.It Oo Ar n Oc Ns Li > Ar file 644redirect stdout (or file descriptor 645.Ar n ) 646to 647.Ar file 648.It Oo Ar n Oc Ns Li >| Ar file 649same as above, but override the 650.Fl C 651option 652.It Oo Ar n Oc Ns Li >> Ar file 653append stdout (or file descriptor 654.Ar n ) 655to 656.Ar file 657.It Oo Ar n Oc Ns Li < Ar file 658redirect stdin (or file descriptor 659.Ar n ) 660from 661.Ar file 662.It Oo Ar n Oc Ns Li <> Ar file 663redirect stdin (or file descriptor 664.Ar n ) 665to and from 666.Ar file 667.It Oo Ar n1 Oc Ns Li <& Ns Ar n2 668duplicate stdin (or file descriptor 669.Ar n1 ) 670from file descriptor 671.Ar n2 672.It Oo Ar n Oc Ns Li <&- 673close stdin (or file descriptor 674.Ar n ) 675.It Oo Ar n1 Oc Ns Li >& Ns Ar n2 676duplicate stdout (or file descriptor 677.Ar n1 ) 678to file descriptor 679.Ar n2 680.It Oo Ar n Oc Ns Li >&- 681close stdout (or file descriptor 682.Ar n ) 683.El 684.Pp 685The following redirection is often called a 686.Dq here-document . 687.Bd -unfilled -offset indent 688.Oo Ar n Oc Ns Li << Ar delimiter 689.Ar here-doc-text 690.Ar ... 691.Ar delimiter 692.Ed 693.Pp 694All the text on successive lines up to the delimiter is 695saved away and made available to the command on standard 696input, or file descriptor 697.Ar n 698if it is specified. 699If the 700.Ar delimiter 701as specified on the initial line is quoted, then the 702.Ar here-doc-text 703is treated literally, otherwise the text is subjected to 704parameter expansion, command substitution, and arithmetic 705expansion (as described in the section on 706.Sx Word Expansions ) . 707If the operator is 708.Dq Li <<- 709instead of 710.Dq Li << , 711then leading tabs 712in the 713.Ar here-doc-text 714are stripped. 715.Ss Search and Execution 716There are three types of commands: shell functions, 717built-in commands, and normal programs. 718The command is searched for (by name) in that order. 719The three types of commands are all executed in a different way. 720.Pp 721When a shell function is executed, all of the shell positional 722parameters (except 723.Li $0 , 724which remains unchanged) are 725set to the arguments of the shell function. 726The variables which are explicitly placed in the environment of 727the command (by placing assignments to them before the 728function name) are made local to the function and are set 729to the values given. 730Then the command given in the function definition is executed. 731The positional parameters are restored to their original values 732when the command completes. 733This all occurs within the current shell. 734.Pp 735Shell built-in commands are executed internally to the shell, without 736spawning a new process. 737There are two kinds of built-in commands: regular and special. 738Assignments before special builtins persist after they finish 739executing and assignment errors, redirection errors and certain 740operand errors cause a script to be aborted. 741Special builtins cannot be overridden with a function. 742Both regular and special builtins can affect the shell in ways 743normal programs cannot. 744.Pp 745Otherwise, if the command name does not match a function 746or built-in command, the command is searched for as a normal 747program in the file system (as described in the next section). 748When a normal program is executed, the shell runs the program, 749passing the arguments and the environment to the program. 750If the program is not a normal executable file 751(i.e., if it does not begin with the 752.Dq "magic number" 753whose ASCII representation is 754.Dq Li #! , 755resulting in an 756.Er ENOEXEC 757return value from 758.Xr execve 2 ) 759but appears to be a text file, 760the shell will run a new instance of 761.Nm 762to interpret it. 763.Pp 764Note that previous versions of this document 765and the source code itself misleadingly and sporadically 766refer to a shell script without a magic number 767as a 768.Dq "shell procedure" . 769.Ss Path Search 770When locating a command, the shell first looks to see if 771it has a shell function by that name. 772Then it looks for a 773built-in command by that name. 774If a built-in command is not found, 775one of two things happen: 776.Bl -enum 777.It 778Command names containing a slash are simply executed without 779performing any searches. 780.It 781The shell searches each entry in the 782.Va PATH 783variable 784in turn for the command. 785The value of the 786.Va PATH 787variable should be a series of 788entries separated by colons. 789Each entry consists of a 790directory name. 791The current directory 792may be indicated implicitly by an empty directory name, 793or explicitly by a single period. 794.El 795.Ss Command Exit Status 796Each command has an exit status that can influence the behavior 797of other shell commands. 798The paradigm is that a command exits 799with zero for normal or success, and non-zero for failure, 800error, or a false indication. 801The man page for each command 802should indicate the various exit codes and what they mean. 803Additionally, the built-in commands return exit codes, as does 804an executed shell function. 805.Pp 806If a command is terminated by a signal, its exit status is greater than 128. 807The signal name can be found by passing the exit status to 808.Li kill -l . 809.Pp 810If there is no command word, 811the exit status is the exit status of the last command substitution executed, 812or zero if the command does not contain any command substitutions. 813.Ss Complex Commands 814Complex commands are combinations of simple commands 815with control operators or keywords, together creating a larger complex 816command. 817More generally, a command is one of the following: 818.Bl -item -offset indent 819.It 820simple command 821.It 822pipeline 823.It 824list or compound-list 825.It 826compound command 827.It 828function definition 829.El 830.Pp 831Unless otherwise stated, the exit status of a command is 832that of the last simple command executed by the command, 833or zero if no simple command was executed. 834.Ss Pipelines 835A pipeline is a sequence of one or more commands separated 836by the control operator 837.Ql \&| . 838The standard output of all but 839the last command is connected to the standard input 840of the next command. 841The standard output of the last 842command is inherited from the shell, as usual. 843.Pp 844The format for a pipeline is: 845.Pp 846.D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ... 847.Pp 848The standard output of 849.Ar command1 850is connected to the standard input of 851.Ar command2 . 852The standard input, standard output, or 853both of a command is considered to be assigned by the 854pipeline before any redirection specified by redirection 855operators that are part of the command. 856.Pp 857Note that unlike some other shells, 858.Nm 859executes each process in a pipeline with more than one command 860in a subshell environment and as a child of the 861.Nm 862process. 863.Pp 864If the pipeline is not in the background (discussed later), 865the shell waits for all commands to complete. 866.Pp 867If the keyword 868.Ic !\& 869does not precede the pipeline, the 870exit status is the exit status of the last command specified 871in the pipeline if the 872.Cm pipefail 873option is not set or all commands returned zero, 874or the last non-zero exit status of any command in the pipeline otherwise. 875Otherwise, the exit status is the logical 876NOT of that exit status. 877That is, if 878that status is zero, the exit status is 1; if 879that status is greater than zero, the exit status 880is zero. 881.Pp 882Because pipeline assignment of standard input or standard 883output or both takes place before redirection, it can be 884modified by redirection. 885For example: 886.Pp 887.Dl "command1 2>&1 | command2" 888.Pp 889sends both the standard output and standard error of 890.Ar command1 891to the standard input of 892.Ar command2 . 893.Pp 894A 895.Ql \&; 896or newline terminator causes the preceding 897AND-OR-list 898(described below in the section called 899.Sx Short-Circuit List Operators ) 900to be executed sequentially; 901an 902.Ql & 903causes asynchronous execution of the preceding AND-OR-list. 904.Ss Background Commands (&) 905If a command is terminated by the control operator ampersand 906.Pq Ql & , 907the shell executes the command in a subshell environment (see 908.Sx Grouping Commands Together 909below) and asynchronously; 910the shell does not wait for the command to finish 911before executing the next command. 912.Pp 913The format for running a command in background is: 914.Pp 915.D1 Ar command1 Li & Op Ar command2 Li & Ar ... 916.Pp 917If the shell is not interactive, the standard input of an 918asynchronous command is set to 919.Pa /dev/null . 920.Pp 921The exit status is zero. 922.Ss Lists (Generally Speaking) 923A list is a sequence of zero or more commands separated by 924newlines, semicolons, or ampersands, 925and optionally terminated by one of these three characters. 926The commands in a 927list are executed in the order they are written. 928If command is followed by an ampersand, the shell starts the 929command and immediately proceeds onto the next command; 930otherwise it waits for the command to terminate before 931proceeding to the next one. 932.Ss Short-Circuit List Operators 933.Dq Li && 934and 935.Dq Li || 936are AND-OR list operators. 937.Dq Li && 938executes the first command, and then executes the second command 939if the exit status of the first command is zero. 940.Dq Li || 941is similar, but executes the second command if the exit 942status of the first command is nonzero. 943.Dq Li && 944and 945.Dq Li || 946both have the same priority. 947.Ss Flow-Control Constructs (if, while, for, case) 948The syntax of the 949.Ic if 950command is: 951.Bd -unfilled -offset indent -compact 952.Ic if Ar list 953.Ic then Ar list 954.Oo Ic elif Ar list 955.Ic then Ar list Oc Ar ... 956.Op Ic else Ar list 957.Ic fi 958.Ed 959.Pp 960The exit status is that of selected 961.Ic then 962or 963.Ic else 964list, 965or zero if no list was selected. 966.Pp 967The syntax of the 968.Ic while 969command is: 970.Bd -unfilled -offset indent -compact 971.Ic while Ar list 972.Ic do Ar list 973.Ic done 974.Ed 975.Pp 976The two lists are executed repeatedly while the exit status of the 977first list is zero. 978The 979.Ic until 980command is similar, but has the word 981.Ic until 982in place of 983.Ic while , 984which causes it to 985repeat until the exit status of the first list is zero. 986.Pp 987The exit status is that of the last execution of the second list, 988or zero if it was never executed. 989.Pp 990The syntax of the 991.Ic for 992command is: 993.Bd -unfilled -offset indent -compact 994.Ic for Ar variable Op Ic in Ar word ... 995.Ic do Ar list 996.Ic done 997.Ed 998.Pp 999If 1000.Ic in 1001and the following words are omitted, 1002.Ic in Li \&"$@\&" 1003is used instead. 1004The words are expanded, and then the list is executed 1005repeatedly with the variable set to each word in turn. 1006The 1007.Ic do 1008and 1009.Ic done 1010commands may be replaced with 1011.Ql { 1012and 1013.Ql } . 1014.Pp 1015The syntax of the 1016.Ic break 1017and 1018.Ic continue 1019commands is: 1020.D1 Ic break Op Ar num 1021.D1 Ic continue Op Ar num 1022.Pp 1023The 1024.Ic break 1025command terminates the 1026.Ar num 1027innermost 1028.Ic for 1029or 1030.Ic while 1031loops. 1032The 1033.Ic continue 1034command continues with the next iteration of the innermost loop. 1035These are implemented as special built-in commands. 1036.Pp 1037The syntax of the 1038.Ic case 1039command is: 1040.Bd -unfilled -offset indent -compact 1041.Ic case Ar word Ic in 1042.Ar pattern ) Ar list Li ;; 1043.Ar ... 1044.Ic esac 1045.Ed 1046.Pp 1047The pattern can actually be one or more patterns 1048(see 1049.Sx Shell Patterns 1050described later), 1051separated by 1052.Ql \&| 1053characters. 1054Tilde expansion, parameter expansion, command substitution, 1055arithmetic expansion and quote removal are applied to the word. 1056Then, each pattern is expanded in turn using tilde expansion, 1057parameter expansion, command substitution and arithmetic expansion and 1058the expanded form of the word is checked against it. 1059If a match is found, the corresponding list is executed. 1060If the selected list is terminated by the control operator 1061.Ql ;& 1062instead of 1063.Ql ;; , 1064execution continues with the next list, 1065continuing until a list terminated with 1066.Ql ;; 1067or the end of the 1068.Ic case 1069command. 1070.Ss Grouping Commands Together 1071Commands may be grouped by writing either 1072.Pp 1073.Sm off 1074.Bd -literal -offset -ident 1075.Po Ar list Pc 1076.Ed 1077.Sm on 1078.Pp 1079or 1080.Bd -literal -offset -ident 1081.No { Ar list ; } 1082.Ed 1083.Pp 1084The first form executes the commands in a subshell environment. 1085A subshell environment has its own copy of: 1086.Bl -enum 1087.It 1088The current working directory as set by 1089.Ic cd . 1090.It 1091The file creation mask as set by 1092.Ic umask . 1093.It 1094Resource limits as set by 1095.Ic ulimit . 1096.It 1097References to open files. 1098.It 1099Traps as set by 1100.Ic trap . 1101.It 1102Known jobs. 1103.It 1104Positional parameters and variables. 1105.It 1106Shell options. 1107.It 1108Shell functions. 1109.It 1110Shell aliases. 1111.El 1112.Pp 1113These are copied from the parent shell environment, 1114except that trapped (but not ignored) signals are reset to the default action 1115and known jobs are cleared. 1116Any changes do not affect the parent shell environment. 1117.Pp 1118A subshell environment may be implemented as a child process or differently. 1119If job control is enabled in an interactive shell, 1120commands grouped in parentheses can be suspended and continued as a unit. 1121.Pp 1122For compatibility with other shells, 1123two open parentheses in sequence should be separated by whitespace. 1124.Pp 1125The second form never forks another shell, 1126so it is slightly more efficient. 1127Grouping commands together this way allows the user to 1128redirect their output as though they were one program: 1129.Bd -literal -offset indent 1130{ echo -n "hello"; echo " world"; } > greeting 1131.Ed 1132.Ss Functions 1133The syntax of a function definition is 1134.Pp 1135.D1 Ar name Li \&( \&) Ar command 1136.Pp 1137A function definition is an executable statement; when 1138executed it installs a function named 1139.Ar name 1140and returns an 1141exit status of zero. 1142The 1143.Ar command 1144is normally a list 1145enclosed between 1146.Ql { 1147and 1148.Ql } . 1149.Pp 1150Variables may be declared to be local to a function by 1151using the 1152.Ic local 1153command. 1154This should appear as the first statement of a function, 1155and the syntax is: 1156.Pp 1157.D1 Ic local Oo Ar variable ... Oc Op Fl 1158.Pp 1159The 1160.Ic local 1161command is implemented as a built-in command. 1162The exit status is zero 1163unless the command is not in a function or a variable name is invalid. 1164.Pp 1165When a variable is made local, it inherits the initial 1166value and exported and readonly flags from the variable 1167with the same name in the surrounding scope, if there is 1168one. 1169Otherwise, the variable is initially unset. 1170The shell 1171uses dynamic scoping, so that if the variable 1172.Va x 1173is made local to function 1174.Em f , 1175which then calls function 1176.Em g , 1177references to the variable 1178.Va x 1179made inside 1180.Em g 1181will refer to the variable 1182.Va x 1183declared inside 1184.Em f , 1185not to the global variable named 1186.Va x . 1187.Pp 1188The only special parameter that can be made local is 1189.Ql - . 1190Making 1191.Ql - 1192local causes any shell options 1193(including those that only have long names) 1194that are 1195changed via the 1196.Ic set 1197command inside the function to be 1198restored to their original values when the function 1199returns. 1200.Pp 1201The syntax of the 1202.Ic return 1203command is 1204.Pp 1205.D1 Ic return Op Ar exitstatus 1206.Pp 1207It terminates the current executional scope, returning from the closest 1208nested function or sourced script; 1209if no function or sourced script is being executed, 1210it exits the shell instance. 1211The 1212.Ic return 1213command is implemented as a special built-in command. 1214.Ss Variables and Parameters 1215The shell maintains a set of parameters. 1216A parameter 1217denoted by a name 1218(consisting solely 1219of alphabetics, numerics, and underscores, 1220and starting with an alphabetic or an underscore) 1221is called a variable. 1222When starting up, 1223the shell turns all environment variables with valid names into shell 1224variables. 1225New variables can be set using the form 1226.Pp 1227.D1 Ar name Ns = Ns Ar value 1228.Pp 1229A parameter can also be denoted by a number 1230or a special character as explained below. 1231.Pp 1232Assignments are expanded differently from other words: 1233tilde expansion is also performed after the equals sign and after any colon 1234and usernames are also terminated by colons, 1235and field splitting and pathname expansion are not performed. 1236.Pp 1237This special expansion applies not only to assignments that form a simple 1238command by themselves or precede a command word, 1239but also to words passed to the 1240.Ic export , 1241.Ic local 1242or 1243.Ic readonly 1244built-in commands that have this form. 1245For this, the builtin's name must be literal 1246(not the result of an expansion) 1247and may optionally be preceded by one or more literal instances of 1248.Ic command 1249without options. 1250.Ss Positional Parameters 1251A positional parameter is a parameter denoted by a number greater than zero. 1252The shell sets these initially to the values of its command line 1253arguments that follow the name of the shell script. 1254The 1255.Ic set 1256built-in command can also be used to set or reset them. 1257.Ss Special Parameters 1258Special parameters are parameters denoted by a single special character 1259or the digit zero. 1260They are shown in the following list, exactly as they would appear in input 1261typed by the user or in the source of a shell script. 1262.Bl -hang 1263.It Li $* 1264Expands to the positional parameters, starting from one. 1265When 1266the expansion occurs within a double-quoted string 1267it expands to a single field with the value of each parameter 1268separated by the first character of the 1269.Va IFS 1270variable, 1271or by a space if 1272.Va IFS 1273is unset. 1274.It Li $@ 1275Expands to the positional parameters, starting from one. 1276When 1277the expansion occurs within double-quotes, each positional 1278parameter expands as a separate argument. 1279If there are no positional parameters, the 1280expansion of 1281.Li @ 1282generates zero arguments, even when 1283.Li @ 1284is double-quoted. 1285What this basically means, for example, is 1286if 1287.Li $1 1288is 1289.Dq Li abc 1290and 1291.Li $2 1292is 1293.Dq Li "def ghi" , 1294then 1295.Li \&"$@\&" 1296expands to 1297the two arguments: 1298.Bd -literal -offset indent 1299"abc" "def ghi" 1300.Ed 1301.It Li $# 1302Expands to the number of positional parameters. 1303.It Li $? 1304Expands to the exit status of the most recent pipeline. 1305.It Li $- 1306(hyphen) Expands to the current option flags (the single-letter 1307option names concatenated into a string) as specified on 1308invocation, by the 1309.Ic set 1310built-in command, or implicitly 1311by the shell. 1312.It Li $$ 1313Expands to the process ID of the invoked shell. 1314A subshell 1315retains the same value of 1316.Va $ 1317as its parent. 1318.It Li $! 1319Expands to the process ID of the most recent background 1320command executed from the current shell. 1321For a 1322pipeline, the process ID is that of the last command in the 1323pipeline. 1324If this parameter is referenced, the shell will remember 1325the process ID and its exit status until the 1326.Ic wait 1327built-in command reports completion of the process. 1328.It Li $0 1329(zero) Expands to the name of the shell script if passed on the command line, 1330the 1331.Ar name 1332operand if given (with 1333.Fl c ) 1334or otherwise argument 0 passed to the shell. 1335.El 1336.Ss Special Variables 1337The following variables are set by the shell or 1338have special meaning to it: 1339.Bl -tag -width ".Va HISTSIZE" 1340.It Va CDPATH 1341The search path used with the 1342.Ic cd 1343built-in. 1344.It Va EDITOR 1345The fallback editor used with the 1346.Ic fc 1347built-in. 1348If not set, the default editor is 1349.Xr ed 1 . 1350.It Va FCEDIT 1351The default editor used with the 1352.Ic fc 1353built-in. 1354.It Va HISTFILE 1355File used for persistent history storage. 1356If unset 1357.Pa ~/.sh_history 1358will be used. 1359If set but empty or 1360.Va HISTSIZE 1361is set to 0 1362the shell will not load and save the history. 1363.It Va HISTSIZE 1364The number of previous commands that are accessible. 1365.It Va HOME 1366The user's home directory, 1367used in tilde expansion and as a default directory for the 1368.Ic cd 1369built-in. 1370.It Va IFS 1371Input Field Separators. 1372This is initialized at startup to 1373.Aq space , 1374.Aq tab , 1375and 1376.Aq newline 1377in that order. 1378This value also applies if 1379.Va IFS 1380is unset, but not if it is set to the empty string. 1381See the 1382.Sx White Space Splitting 1383section for more details. 1384.It Va LINENO 1385The current line number in the script or function. 1386.It Va MAIL 1387The name of a mail file, that will be checked for the arrival of new 1388mail. 1389Overridden by 1390.Va MAILPATH . 1391.It Va MAILPATH 1392A colon 1393.Pq Ql \&: 1394separated list of file names, for the shell to check for incoming 1395mail. 1396This variable overrides the 1397.Va MAIL 1398setting. 1399There is a maximum of 10 mailboxes that can be monitored at once. 1400.It Va OPTIND 1401The index of the next argument to be processed by 1402.Ic getopts . 1403This is initialized to 1 at startup. 1404.It Va PATH 1405The default search path for executables. 1406See the 1407.Sx Path Search 1408section for details. 1409.It Va PPID 1410The parent process ID of the invoked shell. 1411This is set at startup 1412unless this variable is in the environment. 1413A later change of parent process ID is not reflected. 1414A subshell retains the same value of 1415.Va PPID . 1416.It Va PS1 1417The primary prompt string, which defaults to 1418.Dq Li "$ " , 1419unless you are the superuser, in which case it defaults to 1420.Dq Li "# " . 1421.Va PS1 1422may include any of the following formatting sequences, 1423which are replaced by the given information: 1424.Bl -tag -width indent 1425.It Li \eH 1426This system's fully-qualified hostname (FQDN). 1427.It Li \eh 1428This system's hostname. 1429.It Li \eu 1430User name. 1431.It Li \eW 1432The final component of the current working directory. 1433.It Li \ew 1434The entire path of the current working directory. 1435.It Li \e$ 1436Superuser status. 1437.Dq Li "$" 1438for normal users and 1439.Dq Li "#" 1440for superusers. 1441.It Li \e\e 1442A literal backslash. 1443.El 1444.It Va PS2 1445The secondary prompt string, which defaults to 1446.Dq Li "> " . 1447.Va PS2 1448may include any of the formatting sequences from 1449.Va PS1 . 1450.It Va PS4 1451The prefix for the trace output (if 1452.Fl x 1453is active). 1454The default is 1455.Dq Li "+ " . 1456.El 1457.Ss Word Expansions 1458This clause describes the various expansions that are 1459performed on words. 1460Not all expansions are performed on 1461every word, as explained later. 1462.Pp 1463Tilde expansions, parameter expansions, command substitutions, 1464arithmetic expansions, and quote removals that occur within 1465a single word expand to a single field. 1466It is only field 1467splitting or pathname expansion that can create multiple 1468fields from a single word. 1469The single exception to this rule is 1470the expansion of the special parameter 1471.Va @ 1472within double-quotes, 1473as was described above. 1474.Pp 1475The order of word expansion is: 1476.Bl -enum 1477.It 1478Tilde Expansion, Parameter Expansion, Command Substitution, 1479Arithmetic Expansion (these all occur at the same time). 1480.It 1481Field Splitting is performed on fields generated by step (1) 1482unless the 1483.Va IFS 1484variable is null. 1485.It 1486Pathname Expansion (unless the 1487.Fl f 1488option is in effect). 1489.It 1490Quote Removal. 1491.El 1492.Pp 1493The 1494.Ql $ 1495character is used to introduce parameter expansion, command 1496substitution, or arithmetic expansion. 1497.Ss Tilde Expansion (substituting a user's home directory) 1498A word beginning with an unquoted tilde character 1499.Pq Ql ~ 1500is 1501subjected to tilde expansion. 1502All the characters up to a slash 1503.Pq Ql / 1504or the end of the word are treated as a username 1505and are replaced with the user's home directory. 1506If the 1507username is missing (as in 1508.Pa ~/foobar ) , 1509the tilde is replaced with the value of the 1510.Va HOME 1511variable (the current user's home directory). 1512.Ss Parameter Expansion 1513The format for parameter expansion is as follows: 1514.Pp 1515.D1 Li ${ Ns Ar expression Ns Li } 1516.Pp 1517where 1518.Ar expression 1519consists of all characters until the matching 1520.Ql } . 1521Any 1522.Ql } 1523escaped by a backslash or within a single-quoted or double-quoted 1524string, and characters in 1525embedded arithmetic expansions, command substitutions, and variable 1526expansions, are not examined in determining the matching 1527.Ql } . 1528If the variants with 1529.Ql + , 1530.Ql - , 1531.Ql = 1532or 1533.Ql ?\& 1534occur within a double-quoted string, 1535as an extension there may be unquoted parts 1536(via double-quotes inside the expansion); 1537.Ql } 1538within such parts are also not examined in determining the matching 1539.Ql } . 1540.Pp 1541The simplest form for parameter expansion is: 1542.Pp 1543.D1 Li ${ Ns Ar parameter Ns Li } 1544.Pp 1545The value, if any, of 1546.Ar parameter 1547is substituted. 1548.Pp 1549The parameter name or symbol can be enclosed in braces, which are 1550optional except for positional parameters with more than one digit or 1551when parameter is followed by a character that could be interpreted as 1552part of the name. 1553If a parameter expansion occurs inside double-quotes: 1554.Bl -enum 1555.It 1556Field splitting is not performed on the results of the 1557expansion, with the exception of the special parameter 1558.Va @ . 1559.It 1560Pathname expansion is not performed on the results of the 1561expansion. 1562.El 1563.Pp 1564In addition, a parameter expansion can be modified by using one of the 1565following formats. 1566.Bl -tag -width indent 1567.It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li } 1568Use Default Values. 1569If 1570.Ar parameter 1571is unset or null, the expansion of 1572.Ar word 1573is substituted; otherwise, the value of 1574.Ar parameter 1575is substituted. 1576.It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li } 1577Assign Default Values. 1578If 1579.Ar parameter 1580is unset or null, the expansion of 1581.Ar word 1582is assigned to 1583.Ar parameter . 1584In all cases, the 1585final value of 1586.Ar parameter 1587is substituted. 1588Quoting inside 1589.Ar word 1590does not prevent field splitting or pathname expansion. 1591Only variables, not positional 1592parameters or special parameters, can be 1593assigned in this way. 1594.It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li } 1595Indicate Error if Null or Unset. 1596If 1597.Ar parameter 1598is unset or null, the expansion of 1599.Ar word 1600(or a message indicating it is unset if 1601.Ar word 1602is omitted) is written to standard 1603error and the shell exits with a nonzero 1604exit status. 1605Otherwise, the value of 1606.Ar parameter 1607is substituted. 1608An 1609interactive shell need not exit. 1610.It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li } 1611Use Alternate Value. 1612If 1613.Ar parameter 1614is unset or null, null is substituted; 1615otherwise, the expansion of 1616.Ar word 1617is substituted. 1618.El 1619.Pp 1620In the parameter expansions shown previously, use of the colon in the 1621format results in a test for a parameter that is unset or null; omission 1622of the colon results in a test for a parameter that is only unset. 1623.Pp 1624The 1625.Ar word 1626inherits the type of quoting 1627(unquoted, double-quoted or here-document) 1628from the surroundings, 1629with the exception that a backslash that quotes a closing brace is removed 1630during quote removal. 1631.Bl -tag -width indent 1632.It Li ${# Ns Ar parameter Ns Li } 1633String Length. 1634The length in characters of 1635the value of 1636.Ar parameter . 1637.El 1638.Pp 1639The following four varieties of parameter expansion provide for substring 1640processing. 1641In each case, pattern matching notation 1642(see 1643.Sx Shell Patterns ) , 1644rather than regular expression notation, 1645is used to evaluate the patterns. 1646If parameter is one of the special parameters 1647.Va * 1648or 1649.Va @ , 1650the result of the expansion is unspecified. 1651Enclosing the full parameter expansion string in double-quotes does not 1652cause the following four varieties of pattern characters to be quoted, 1653whereas quoting characters within the braces has this effect. 1654.Bl -tag -width indent 1655.It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li } 1656Remove Smallest Suffix Pattern. 1657The 1658.Ar word 1659is expanded to produce a pattern. 1660The 1661parameter expansion then results in 1662.Ar parameter , 1663with the smallest portion of the 1664suffix matched by the pattern deleted. 1665.It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li } 1666Remove Largest Suffix Pattern. 1667The 1668.Ar word 1669is expanded to produce a pattern. 1670The 1671parameter expansion then results in 1672.Ar parameter , 1673with the largest portion of the 1674suffix matched by the pattern deleted. 1675.It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li } 1676Remove Smallest Prefix Pattern. 1677The 1678.Ar word 1679is expanded to produce a pattern. 1680The 1681parameter expansion then results in 1682.Ar parameter , 1683with the smallest portion of the 1684prefix matched by the pattern deleted. 1685.It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li } 1686Remove Largest Prefix Pattern. 1687The 1688.Ar word 1689is expanded to produce a pattern. 1690The 1691parameter expansion then results in 1692.Ar parameter , 1693with the largest portion of the 1694prefix matched by the pattern deleted. 1695.El 1696.Ss Command Substitution 1697Command substitution allows the output of a command to be substituted in 1698place of the command name itself. 1699Command substitution occurs when 1700the command is enclosed as follows: 1701.Pp 1702.D1 Li $( Ns Ar command Ns Li )\& 1703.Pp 1704or the backquoted version: 1705.Pp 1706.D1 Li ` Ns Ar command Ns Li ` 1707.Pp 1708The shell expands the command substitution by executing command 1709and replacing the command substitution 1710with the standard output of the command, 1711removing sequences of one or more newlines at the end of the substitution. 1712Embedded newlines before the end of the output are not removed; 1713however, during field splitting, they may be translated into spaces 1714depending on the value of 1715.Va IFS 1716and the quoting that is in effect. 1717The command is executed in a subshell environment, 1718except that the built-in commands 1719.Ic jobid , 1720.Ic jobs , 1721and 1722.Ic trap 1723return information about the parent shell environment 1724and 1725.Ic times 1726returns information about the same process 1727if they are the only command in a command substitution. 1728.Pp 1729If a command substitution of the 1730.Li $( 1731form begins with a subshell, 1732the 1733.Li $( 1734and 1735.Li (\& 1736must be separated by whitespace 1737to avoid ambiguity with arithmetic expansion. 1738.Ss Arithmetic Expansion 1739Arithmetic expansion provides a mechanism for evaluating an arithmetic 1740expression and substituting its value. 1741The format for arithmetic expansion is as follows: 1742.Pp 1743.D1 Li $(( Ns Ar expression Ns Li )) 1744.Pp 1745The 1746.Ar expression 1747is treated as if it were in double-quotes, except 1748that a double-quote inside the expression is not treated specially. 1749The 1750shell expands all tokens in the 1751.Ar expression 1752for parameter expansion, 1753command substitution, 1754arithmetic expansion 1755and quote removal. 1756.Pp 1757The allowed expressions are a subset of C expressions, 1758summarized below. 1759.Bl -tag -width "Variables" -offset indent 1760.It Values 1761All values are of type 1762.Ft intmax_t . 1763.It Constants 1764Decimal, octal (starting with 1765.Li 0 ) 1766and hexadecimal (starting with 1767.Li 0x ) 1768integer constants. 1769.It Variables 1770Shell variables can be read and written 1771and contain integer constants. 1772.It Unary operators 1773.Li "! ~ + -" 1774.It Binary operators 1775.Li "* / % + - << >> < <= > >= == != & ^ | && ||"\& 1776.It Assignment operators 1777.Li "= += -= *= /= %= <<= >>= &= ^= |=" 1778.It Conditional operator 1779.Li "? :"\& 1780.El 1781.Pp 1782The result of the expression is substituted in decimal. 1783.Ss White Space Splitting (Field Splitting) 1784In certain contexts, 1785after parameter expansion, command substitution, and 1786arithmetic expansion the shell scans the results of 1787expansions and substitutions that did not occur in double-quotes for 1788field splitting and multiple fields can result. 1789.Pp 1790Characters in 1791.Va IFS 1792that are whitespace 1793.Po 1794.Aq space , 1795.Aq tab , 1796and 1797.Aq newline 1798.Pc 1799are treated differently from other characters in 1800.Va IFS . 1801.Pp 1802Whitespace in 1803.Va IFS 1804at the beginning or end of a word is discarded. 1805.Pp 1806Subsequently, a field is delimited by either 1807.Bl -enum 1808.It 1809a non-whitespace character in 1810.Va IFS 1811with any whitespace in 1812.Va IFS 1813surrounding it, or 1814.It 1815one or more whitespace characters in 1816.Va IFS . 1817.El 1818.Pp 1819If a word ends with a non-whitespace character in 1820.Va IFS , 1821there is no empty field after this character. 1822.Pp 1823If no field is delimited, the word is discarded. 1824In particular, if a word consists solely of an unquoted substitution 1825and the result of the substitution is null, 1826it is removed by field splitting even if 1827.Va IFS 1828is null. 1829.Ss Pathname Expansion (File Name Generation) 1830Unless the 1831.Fl f 1832option is set, 1833file name generation is performed 1834after word splitting is complete. 1835Each word is 1836viewed as a series of patterns, separated by slashes. 1837The 1838process of expansion replaces the word with the names of 1839all existing files whose names can be formed by replacing 1840each pattern with a string that matches the specified pattern. 1841There are two restrictions on this: first, a pattern cannot match 1842a string containing a slash, and second, 1843a pattern cannot match a string starting with a period 1844unless the first character of the pattern is a period. 1845The next section describes the patterns used for 1846Pathname Expansion, 1847the four varieties of parameter expansion for substring processing and the 1848.Ic case 1849command. 1850.Ss Shell Patterns 1851A pattern consists of normal characters, which match themselves, 1852and meta-characters. 1853The meta-characters are 1854.Ql * , 1855.Ql \&? , 1856and 1857.Ql \&[ . 1858These characters lose their special meanings if they are quoted. 1859When command or variable substitution is performed and the dollar sign 1860or back quotes are not double-quoted, the value of the 1861variable or the output of the command is scanned for these 1862characters and they are turned into meta-characters. 1863.Pp 1864An asterisk 1865.Pq Ql * 1866matches any string of characters. 1867A question mark 1868.Pq Ql \&? 1869matches any single character. 1870A left bracket 1871.Pq Ql \&[ 1872introduces a character class. 1873The end of the character class is indicated by a 1874.Ql \&] ; 1875if the 1876.Ql \&] 1877is missing then the 1878.Ql \&[ 1879matches a 1880.Ql \&[ 1881rather than introducing a character class. 1882A character class matches any of the characters between the square brackets. 1883A locale-dependent range of characters may be specified using a minus sign. 1884A named class of characters (see 1885.Xr wctype 3 ) 1886may be specified by surrounding the name with 1887.Ql \&[:\& 1888and 1889.Ql :\&] . 1890For example, 1891.Ql \&[\&[:alpha:\&]\&] 1892is a shell pattern that matches a single letter. 1893The character class may be complemented by making an exclamation point 1894.Pq Ql !\& 1895the first character of the character class. 1896A caret 1897.Pq Ql ^ 1898has the same effect but is non-standard. 1899.Pp 1900To include a 1901.Ql \&] 1902in a character class, make it the first character listed 1903(after the 1904.Ql \&! 1905or 1906.Ql ^ , 1907if any). 1908To include a 1909.Ql - , 1910make it the first or last character listed. 1911.Ss Built-in Commands 1912This section lists the built-in commands. 1913.Bl -tag -width indent 1914.It Ic \&: 1915A null command that returns a 0 (true) exit value. 1916.It Ic \&. Ar file 1917The commands in the specified file are read and executed by the shell. 1918The 1919.Ic return 1920command may be used to return to the 1921.Ic \&. 1922command's caller. 1923If 1924.Ar file 1925contains any 1926.Ql / 1927characters, it is used as is. 1928Otherwise, the shell searches the 1929.Va PATH 1930for the file. 1931If it is not found in the 1932.Va PATH , 1933it is sought in the current working directory. 1934.It Ic \&[ 1935A built-in equivalent of 1936.Xr test 1 . 1937.It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc 1938If 1939.Ar name Ns = Ns Ar string 1940is specified, the shell defines the alias 1941.Ar name 1942with value 1943.Ar string . 1944If just 1945.Ar name 1946is specified, the value of the alias 1947.Ar name 1948is printed. 1949With no arguments, the 1950.Ic alias 1951built-in command prints the names and values of all defined aliases 1952(see 1953.Ic unalias ) . 1954Alias values are written with appropriate quoting so that they are 1955suitable for re-input to the shell. 1956Also see the 1957.Sx Aliases 1958subsection. 1959.It Ic bg Op Ar job ... 1960Continue the specified jobs 1961(or the current job if no jobs are given) 1962in the background. 1963.It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc 1964List or alter key bindings for the line editor. 1965This command is documented in 1966.Xr editrc 5 . 1967.It Ic break Op Ar num 1968See the 1969.Sx Flow-Control Constructs 1970subsection. 1971.It Ic builtin Ar cmd Op Ar arg ... 1972Execute the specified built-in command, 1973.Ar cmd . 1974This is useful when the user wishes to override a shell function 1975with the same name as a built-in command. 1976.It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory 1977.It Ic cd Fl 1978Switch to the specified 1979.Ar directory , 1980to the directory specified in the 1981.Va HOME 1982environment variable if no 1983.Ar directory 1984is specified or 1985to the directory specified in the 1986.Va OLDPWD 1987environment variable if 1988.Ar directory 1989is 1990.Fl . 1991If 1992.Ar directory 1993does not begin with 1994.Pa / , \&. , 1995or 1996.Pa .. , 1997then the directories listed in the 1998.Va CDPATH 1999variable will be 2000searched for the specified 2001.Ar directory . 2002If 2003.Va CDPATH 2004is unset, the current directory is searched. 2005The format of 2006.Va CDPATH 2007is the same as that of 2008.Va PATH . 2009In an interactive shell, 2010the 2011.Ic cd 2012command will print out the name of the directory 2013that it actually switched to 2014if the 2015.Va CDPATH 2016mechanism was used or if 2017.Ar directory 2018was 2019.Fl . 2020.Pp 2021If the 2022.Fl P 2023option is specified, 2024.Pa .. 2025is handled physically and symbolic links are resolved before 2026.Pa .. 2027components are processed. 2028If the 2029.Fl L 2030option is specified, 2031.Pa .. 2032is handled logically. 2033This is the default. 2034.Pp 2035The 2036.Fl e 2037option causes 2038.Ic cd 2039to return exit status 1 if the full pathname of the new directory 2040cannot be determined reliably or at all. 2041Normally this is not considered an error, 2042although a warning is printed. 2043.Pp 2044If changing the directory fails, the exit status is greater than 1. 2045If the directory is changed, the exit status is 0, or also 1 if 2046.Fl e 2047was given. 2048.It Ic chdir 2049A synonym for the 2050.Ic cd 2051built-in command. 2052.It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ... 2053.It Ic command Oo Fl p Oc Fl v Ar utility 2054.It Ic command Oo Fl p Oc Fl V Ar utility 2055The first form of invocation executes the specified 2056.Ar utility , 2057ignoring shell functions in the search. 2058If 2059.Ar utility 2060is a special builtin, 2061it is executed as if it were a regular builtin. 2062.Pp 2063If the 2064.Fl p 2065option is specified, the command search is performed using a 2066default value of 2067.Va PATH 2068that is guaranteed to find all of the standard utilities. 2069.Pp 2070If the 2071.Fl v 2072option is specified, 2073.Ar utility 2074is not executed but a description of its interpretation by the shell is 2075printed. 2076For ordinary commands the output is the path name; for shell built-in 2077commands, shell functions and keywords only the name is written. 2078Aliases are printed as 2079.Dq Ic alias Ar name Ns = Ns Ar value . 2080.Pp 2081The 2082.Fl V 2083option is identical to 2084.Fl v 2085except for the output. 2086It prints 2087.Dq Ar utility Ic is Ar description 2088where 2089.Ar description 2090is either 2091the path name to 2092.Ar utility , 2093a special shell builtin, 2094a shell builtin, 2095a shell function, 2096a shell keyword 2097or 2098an alias for 2099.Ar value . 2100.It Ic continue Op Ar num 2101See the 2102.Sx Flow-Control Constructs 2103subsection. 2104.It Ic echo Oo Fl e | n Oc Op Ar string ... 2105Print a space-separated list of the arguments to the standard output 2106and append a newline character. 2107.Bl -tag -width indent 2108.It Fl n 2109Suppress the output of the trailing newline. 2110.It Fl e 2111Process C-style backslash escape sequences. 2112The 2113.Ic echo 2114command understands the following character escapes: 2115.Bl -tag -width indent 2116.It \ea 2117Alert (ring the terminal bell) 2118.It \eb 2119Backspace 2120.It \ec 2121Suppress the trailing newline (this has the side-effect of truncating the 2122line if it is not the last character) 2123.It \ee 2124The ESC character (ASCII 0x1b) 2125.It \ef 2126Formfeed 2127.It \en 2128Newline 2129.It \er 2130Carriage return 2131.It \et 2132Horizontal tab 2133.It \ev 2134Vertical tab 2135.It \e\e 2136Literal backslash 2137.It \e0nnn 2138(Zero) The character whose octal value is 2139.Ar nnn 2140.El 2141.Pp 2142If 2143.Ar string 2144is not enclosed in quotes then the backslash itself must be escaped 2145with a backslash to protect it from the shell. 2146For example 2147.Bd -literal -offset indent 2148$ echo -e "a\evb" 2149a 2150 b 2151$ echo -e a\e\evb 2152a 2153 b 2154$ echo -e "a\e\eb" 2155a\eb 2156$ echo -e a\e\e\e\eb 2157a\eb 2158.Ed 2159.El 2160.Pp 2161Only one of the 2162.Fl e 2163and 2164.Fl n 2165options may be specified. 2166.It Ic eval Ar string ... 2167Concatenate all the arguments with spaces. 2168Then re-parse and execute the command. 2169.It Ic exec Op Ar command Op arg ... 2170Unless 2171.Ar command 2172is omitted, 2173the shell process is replaced with the specified program 2174(which must be a real program, not a shell built-in command or function). 2175Any redirections on the 2176.Ic exec 2177command are marked as permanent, 2178so that they are not undone when the 2179.Ic exec 2180command finishes. 2181.It Ic exit Op Ar exitstatus 2182Terminate the shell process. 2183If 2184.Ar exitstatus 2185is given 2186it is used as the exit status of the shell. 2187Otherwise, if the shell is executing an 2188.Cm EXIT 2189trap, the exit status of the last command before the trap is used; 2190if the shell is executing a trap for a signal, 2191the shell exits by resending the signal to itself. 2192Otherwise, the exit status of the preceding command is used. 2193The exit status should be an integer between 0 and 255. 2194.It Ic export Ar name ... 2195.It Ic export Op Fl p 2196The specified names are exported so that they will 2197appear in the environment of subsequent commands. 2198The only way to un-export a variable is to 2199.Ic unset 2200it. 2201The shell allows the value of a variable to be set 2202at the same time as it is exported by writing 2203.Pp 2204.D1 Ic export Ar name Ns = Ns Ar value 2205.Pp 2206With no arguments the 2207.Ic export 2208command lists the names 2209of all exported variables. 2210If the 2211.Fl p 2212option is specified, the exported variables are printed as 2213.Dq Ic export Ar name Ns = Ns Ar value 2214lines, suitable for re-input to the shell. 2215.It Ic false 2216A null command that returns a non-zero (false) exit value. 2217.It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last 2218.It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last 2219.It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first 2220The 2221.Ic fc 2222built-in command lists, or edits and re-executes, 2223commands previously entered to an interactive shell. 2224.Bl -tag -width indent 2225.It Fl e Ar editor 2226Use the editor named by 2227.Ar editor 2228to edit the commands. 2229The 2230.Ar editor 2231string is a command name, 2232subject to search via the 2233.Va PATH 2234variable. 2235The value in the 2236.Va FCEDIT 2237variable is used as a default when 2238.Fl e 2239is not specified. 2240If 2241.Va FCEDIT 2242is null or unset, the value of the 2243.Va EDITOR 2244variable is used. 2245If 2246.Va EDITOR 2247is null or unset, 2248.Xr ed 1 2249is used as the editor. 2250.It Fl l No (ell) 2251List the commands rather than invoking 2252an editor on them. 2253The commands are written in the 2254sequence indicated by the 2255.Ar first 2256and 2257.Ar last 2258operands, as affected by 2259.Fl r , 2260with each command preceded by the command number. 2261.It Fl n 2262Suppress command numbers when listing with 2263.Fl l . 2264.It Fl r 2265Reverse the order of the commands listed 2266(with 2267.Fl l ) 2268or edited 2269(with neither 2270.Fl l 2271nor 2272.Fl s ) . 2273.It Fl s 2274Re-execute the command without invoking an editor. 2275.It Ar first 2276.It Ar last 2277Select the commands to list or edit. 2278The number of previous commands that can be accessed 2279are determined by the value of the 2280.Va HISTSIZE 2281variable. 2282The value of 2283.Ar first 2284or 2285.Ar last 2286or both are one of the following: 2287.Bl -tag -width indent 2288.It Oo Cm + Oc Ns Ar num 2289A positive number representing a command number; 2290command numbers can be displayed with the 2291.Fl l 2292option. 2293.It Fl Ar num 2294A negative decimal number representing the 2295command that was executed 2296.Ar num 2297of 2298commands previously. 2299For example, \-1 is the immediately previous command. 2300.It Ar string 2301A string indicating the most recently entered command 2302that begins with that string. 2303If the 2304.Ar old Ns = Ns Ar new 2305operand is not also specified with 2306.Fl s , 2307the string form of the first operand cannot contain an embedded equal sign. 2308.El 2309.El 2310.Pp 2311The following variables affect the execution of 2312.Ic fc : 2313.Bl -tag -width ".Va HISTSIZE" 2314.It Va FCEDIT 2315Name of the editor to use for history editing. 2316.It Va HISTSIZE 2317The number of previous commands that are accessible. 2318.El 2319.It Ic fg Op Ar job 2320Move the specified 2321.Ar job 2322or the current job to the foreground. 2323.It Ic getopts Ar optstring var 2324The POSIX 2325.Ic getopts 2326command. 2327The 2328.Ic getopts 2329command deprecates the older 2330.Xr getopt 1 2331command. 2332The first argument should be a series of letters, each possibly 2333followed by a colon which indicates that the option takes an argument. 2334The specified variable is set to the parsed option. 2335The index of 2336the next argument is placed into the shell variable 2337.Va OPTIND . 2338If an option takes an argument, it is placed into the shell variable 2339.Va OPTARG . 2340If an invalid option is encountered, 2341.Ar var 2342is set to 2343.Ql \&? . 2344It returns a false value (1) when it encounters the end of the options. 2345A new set of arguments may be parsed by assigning 2346.Li OPTIND=1 . 2347.It Ic hash Oo Fl rv Oc Op Ar command ... 2348The shell maintains a hash table which remembers the locations of commands. 2349With no arguments whatsoever, the 2350.Ic hash 2351command prints out the contents of this table. 2352.Pp 2353With arguments, the 2354.Ic hash 2355command removes each specified 2356.Ar command 2357from the hash table (unless they are functions) and then locates it. 2358With the 2359.Fl v 2360option, 2361.Ic hash 2362prints the locations of the commands as it finds them. 2363The 2364.Fl r 2365option causes the 2366.Ic hash 2367command to delete all the entries in the hash table except for functions. 2368.It Ic jobid Op Ar job 2369Print the process IDs of the processes in the specified 2370.Ar job . 2371If the 2372.Ar job 2373argument is omitted, use the current job. 2374.It Ic jobs Oo Fl lps Oc Op Ar job ... 2375Print information about the specified jobs, or all jobs if no 2376.Ar job 2377argument is given. 2378The information printed includes job ID, status and command name. 2379.Pp 2380If the 2381.Fl l 2382option is specified, the PID of each job is also printed. 2383If the 2384.Fl p 2385option is specified, only the process IDs for the process group leaders 2386are printed, one per line. 2387If the 2388.Fl s 2389option is specified, only the PIDs of the job commands are printed, one per 2390line. 2391.It Ic kill 2392A built-in equivalent of 2393.Xr kill 1 2394that additionally supports sending signals to jobs. 2395.It Ic local Oo Ar variable ... Oc Op Fl 2396See the 2397.Sx Functions 2398subsection. 2399.It Ic printf 2400A built-in equivalent of 2401.Xr printf 1 . 2402.It Ic pwd Op Fl L | P 2403Print the path of the current directory. 2404The built-in command may 2405differ from the program of the same name because the 2406built-in command remembers what the current directory 2407is rather than recomputing it each time. 2408This makes 2409it faster. 2410However, if the current directory is 2411renamed, 2412the built-in version of 2413.Xr pwd 1 2414will continue to print the old name for the directory. 2415.Pp 2416If the 2417.Fl P 2418option is specified, symbolic links are resolved. 2419If the 2420.Fl L 2421option is specified, the shell's notion of the current directory 2422is printed (symbolic links are not resolved). 2423This is the default. 2424.It Ic read Oo Fl p Ar prompt Oc Oo 2425.Fl t Ar timeout Oc Oo Fl er Oc Ar variable ... 2426The 2427.Ar prompt 2428is printed if the 2429.Fl p 2430option is specified 2431and the standard input is a terminal. 2432Then a line is 2433read from the standard input. 2434The trailing newline 2435is deleted from the line and the line is split as 2436described in the section on 2437.Sx White Space Splitting (Field Splitting)\& 2438above, and 2439the pieces are assigned to the variables in order. 2440If there are more pieces than variables, the remaining 2441pieces (along with the characters in 2442.Va IFS 2443that separated them) 2444are assigned to the last variable. 2445If there are more variables than pieces, the remaining 2446variables are assigned the null string. 2447.Pp 2448Backslashes are treated specially, unless the 2449.Fl r 2450option is 2451specified. 2452If a backslash is followed by 2453a newline, the backslash and the newline will be 2454deleted. 2455If a backslash is followed by any other 2456character, the backslash will be deleted and the following 2457character will be treated as though it were not in 2458.Va IFS , 2459even if it is. 2460.Pp 2461If the 2462.Fl t 2463option is specified and the 2464.Ar timeout 2465elapses before a complete line of input is supplied, 2466the 2467.Ic read 2468command will return an exit status as if terminated by 2469.Dv SIGALRM 2470without assigning any values. 2471The 2472.Ar timeout 2473value may optionally be followed by one of 2474.Ql s , 2475.Ql m 2476or 2477.Ql h 2478to explicitly specify seconds, minutes or hours. 2479If none is supplied, 2480.Ql s 2481is assumed. 2482.Pp 2483The 2484.Fl e 2485option exists only for backward compatibility with older scripts. 2486.Pp 2487The exit status is 0 on success, 1 on end of file, 2488between 2 and 128 if an error occurs 2489and greater than 128 if a trapped signal interrupts 2490.Ic read . 2491.It Ic readonly Oo Fl p Oc Op Ar name ... 2492Each specified 2493.Ar name 2494is marked as read only, 2495so that it cannot be subsequently modified or unset. 2496The shell allows the value of a variable to be set 2497at the same time as it is marked read only 2498by using the following form: 2499.Pp 2500.D1 Ic readonly Ar name Ns = Ns Ar value 2501.Pp 2502With no arguments the 2503.Ic readonly 2504command lists the names of all read only variables. 2505If the 2506.Fl p 2507option is specified, the read-only variables are printed as 2508.Dq Ic readonly Ar name Ns = Ns Ar value 2509lines, suitable for re-input to the shell. 2510.It Ic return Op Ar exitstatus 2511See the 2512.Sx Functions 2513subsection. 2514.It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname 2515.Oc Op Fl - Ar arg ... 2516The 2517.Ic set 2518command performs three different functions: 2519.Bl -item 2520.It 2521With no arguments, it lists the values of all shell variables. 2522.It 2523If options are given, 2524either in short form or using the long 2525.Dq Fl /+o Ar longname 2526form, 2527it sets or clears the specified options as described in the section called 2528.Sx Argument List Processing . 2529.It 2530If the 2531.Dq Fl - 2532option is specified, 2533.Ic set 2534will replace the shell's positional parameters with the subsequent 2535arguments. 2536If no arguments follow the 2537.Dq Fl - 2538option, 2539all the positional parameters will be cleared, 2540which is equivalent to executing the command 2541.Dq Li "shift $#" . 2542The 2543.Dq Fl - 2544flag may be omitted when specifying arguments to be used 2545as positional replacement parameters. 2546This is not recommended, 2547because the first argument may begin with a dash 2548.Pq Ql - 2549or a plus 2550.Pq Ql + , 2551which the 2552.Ic set 2553command will interpret as a request to enable or disable options. 2554.El 2555.It Ic setvar Ar variable value 2556Assigns the specified 2557.Ar value 2558to the specified 2559.Ar variable . 2560The 2561.Ic setvar 2562command is intended to be used in functions that 2563assign values to variables whose names are passed as parameters. 2564In general it is better to write 2565.Dq Ar variable Ns = Ns Ar value 2566rather than using 2567.Ic setvar . 2568.It Ic shift Op Ar n 2569Shift the positional parameters 2570.Ar n 2571times, or once if 2572.Ar n 2573is not specified. 2574A shift sets the value of 2575.Li $1 2576to the value of 2577.Li $2 , 2578the value of 2579.Li $2 2580to the value of 2581.Li $3 , 2582and so on, 2583decreasing the value of 2584.Li $# 2585by one. 2586For portability, shifting if there are zero positional parameters 2587should be avoided, since the shell may abort. 2588.It Ic test 2589A built-in equivalent of 2590.Xr test 1 . 2591.It Ic times 2592Print the amount of time spent executing the shell process and its children. 2593The first output line shows the user and system times for the shell process 2594itself, the second one contains the user and system times for the 2595children. 2596.It Ic trap Oo Ar action Oc Ar signal ... 2597.It Ic trap Fl l 2598Cause the shell to parse and execute 2599.Ar action 2600when any specified 2601.Ar signal 2602is received. 2603The signals are specified by name or number. 2604In addition, the pseudo-signal 2605.Cm EXIT 2606may be used to specify an 2607.Ar action 2608that is performed when the shell terminates. 2609The 2610.Ar action 2611may be an empty string or a dash 2612.Pq Ql - ; 2613the former causes the specified signal to be ignored 2614and the latter causes the default action to be taken. 2615Omitting the 2616.Ar action 2617and using only signal numbers is another way to request the default action. 2618In a subshell or utility environment, 2619the shell resets trapped (but not ignored) signals to the default action. 2620The 2621.Ic trap 2622command has no effect on signals that were ignored on entry to the shell. 2623.Pp 2624Option 2625.Fl l 2626causes the 2627.Ic trap 2628command to display a list of valid signal names. 2629.It Ic true 2630A null command that returns a 0 (true) exit value. 2631.It Ic type Op Ar name ... 2632Interpret each 2633.Ar name 2634as a command and print the resolution of the command search. 2635Possible resolutions are: 2636shell keyword, alias, special shell builtin, shell builtin, command, 2637tracked alias 2638and not found. 2639For aliases the alias expansion is printed; 2640for commands and tracked aliases 2641the complete pathname of the command is printed. 2642.It Ic ulimit Oo Fl HSabcdfklmnopstuvw Oc Op Ar limit 2643Set or display resource limits (see 2644.Xr getrlimit 2 ) . 2645If 2646.Ar limit 2647is specified, the named resource will be set; 2648otherwise the current resource value will be displayed. 2649.Pp 2650If 2651.Fl H 2652is specified, the hard limits will be set or displayed. 2653While everybody is allowed to reduce a hard limit, 2654only the superuser can increase it. 2655The 2656.Fl S 2657option 2658specifies the soft limits instead. 2659When displaying limits, 2660only one of 2661.Fl S 2662or 2663.Fl H 2664can be given. 2665The default is to display the soft limits, 2666and to set both the hard and the soft limits. 2667.Pp 2668Option 2669.Fl a 2670causes the 2671.Ic ulimit 2672command to display all resources. 2673The parameter 2674.Ar limit 2675is not acceptable in this mode. 2676.Pp 2677The remaining options specify which resource value is to be 2678displayed or modified. 2679They are mutually exclusive. 2680.Bl -tag -width indent 2681.It Fl b Ar sbsize 2682The maximum size of socket buffer usage, in bytes. 2683.It Fl c Ar coredumpsize 2684The maximal size of core dump files, in 512-byte blocks. 2685Setting 2686.Ar coredumpsize 2687to 0 prevents core dump files from being created. 2688.It Fl d Ar datasize 2689The maximal size of the data segment of a process, in kilobytes. 2690.It Fl f Ar filesize 2691The maximal size of a file, in 512-byte blocks. 2692.It Fl k Ar kqueues 2693The maximal number of kqueues 2694(see 2695.Xr kqueue 2 ) 2696for this user ID. 2697.It Fl l Ar lockedmem 2698The maximal size of memory that can be locked by a process, in 2699kilobytes. 2700.It Fl m Ar memoryuse 2701The maximal resident set size of a process, in kilobytes. 2702.It Fl n Ar nofiles 2703The maximal number of descriptors that could be opened by a process. 2704.It Fl o Ar umtxp 2705The maximal number of process-shared locks 2706(see 2707.Xr pthread 3 ) 2708for this user ID. 2709.It Fl p Ar pseudoterminals 2710The maximal number of pseudo-terminals for this user ID. 2711.It Fl s Ar stacksize 2712The maximal size of the stack segment, in kilobytes. 2713.It Fl t Ar time 2714The maximal amount of CPU time to be used by each process, in seconds. 2715.It Fl u Ar userproc 2716The maximal number of simultaneous processes for this user ID. 2717.It Fl v Ar virtualmem 2718The maximal virtual size of a process, in kilobytes. 2719.It Fl w Ar swapuse 2720The maximum amount of swap space reserved or used for this user ID, 2721in kilobytes. 2722.El 2723.It Ic umask Oo Fl S Oc Op Ar mask 2724Set the file creation mask (see 2725.Xr umask 2 ) 2726to the octal or symbolic (see 2727.Xr chmod 1 ) 2728value specified by 2729.Ar mask . 2730If the argument is omitted, the current mask value is printed. 2731If the 2732.Fl S 2733option is specified, the output is symbolic, otherwise the output is octal. 2734.It Ic unalias Oo Fl a Oc Op Ar name ... 2735The specified alias names are removed. 2736If 2737.Fl a 2738is specified, all aliases are removed. 2739.It Ic unset Oo Fl fv Oc Ar name ... 2740The specified variables or functions are unset and unexported. 2741If the 2742.Fl v 2743option is specified or no options are given, the 2744.Ar name 2745arguments are treated as variable names. 2746If the 2747.Fl f 2748option is specified, the 2749.Ar name 2750arguments are treated as function names. 2751.It Ic wait Op Ar job ... 2752Wait for each specified 2753.Ar job 2754to complete and return the exit status of the last process in the 2755last specified 2756.Ar job . 2757If any 2758.Ar job 2759specified is unknown to the shell, it is treated as if it 2760were a known job that exited with exit status 127. 2761If no operands are given, wait for all jobs to complete 2762and return an exit status of zero. 2763.El 2764.Ss Command Line Editing 2765When 2766.Nm 2767is being used interactively from a terminal, the current command 2768and the command history 2769(see 2770.Ic fc 2771in 2772.Sx Built-in Commands ) 2773can be edited using 2774.Nm vi Ns -mode 2775command line editing. 2776This mode uses commands similar 2777to a subset of those described in the 2778.Xr vi 1 2779man page. 2780The command 2781.Dq Li "set -o vi" 2782(or 2783.Dq Li "set -V" ) 2784enables 2785.Nm vi Ns -mode 2786editing and places 2787.Nm 2788into 2789.Nm vi 2790insert mode. 2791With 2792.Nm vi Ns -mode 2793enabled, 2794.Nm 2795can be switched between insert mode and command mode by typing 2796.Aq ESC . 2797Hitting 2798.Aq return 2799while in command mode will pass the line to the shell. 2800.Pp 2801Similarly, the 2802.Dq Li "set -o emacs" 2803(or 2804.Dq Li "set -E" ) 2805command can be used to enable a subset of 2806.Nm emacs Ns -style 2807command line editing features. 2808.Sh ENVIRONMENT 2809The following environment variables affect the execution of 2810.Nm : 2811.Bl -tag -width ".Ev LANGXXXXXX" 2812.It Ev ENV 2813Initialization file for interactive shells. 2814.It Ev LANG , Ev LC_* 2815Locale settings. 2816These are inherited by children of the shell, 2817and is used in a limited manner by the shell itself. 2818.It Ev OLDPWD 2819The previous current directory. 2820This is used and updated by 2821.Ic cd . 2822.It Ev PWD 2823An absolute pathname for the current directory, 2824possibly containing symbolic links. 2825This is used and updated by the shell. 2826.It Ev TERM 2827The default terminal setting for the shell. 2828This is inherited by children of the shell, and is used in the history 2829editing modes. 2830.El 2831.Pp 2832Additionally, environment variables are turned into shell variables 2833at startup, 2834which may affect the shell as described under 2835.Sx Special Variables . 2836.Sh FILES 2837.Bl -tag -width "/etc/suid_profileXX" -compact 2838.It Pa ~/.profile 2839User's login profile. 2840.It Pa /etc/profile 2841System login profile. 2842.It Pa /etc/shells 2843Shell database. 2844.It Pa /etc/suid_profile 2845Privileged shell profile. 2846.El 2847.Sh EXIT STATUS 2848If the 2849.Ar script 2850cannot be found, the exit status will be 127; 2851if it cannot be opened for another reason, the exit status will be 126. 2852Other errors that are detected by the shell, such as a syntax error, will 2853cause the shell to exit with a non-zero exit status. 2854If the shell is not an interactive shell, the execution of the shell 2855file will be aborted. 2856Otherwise the shell will return the exit status of the last command 2857executed, or if the 2858.Ic exit 2859builtin is used with a numeric argument, it 2860will return the argument. 2861.Sh SEE ALSO 2862.Xr builtin 1 , 2863.Xr chsh 1 , 2864.Xr echo 1 , 2865.Xr ed 1 , 2866.Xr emacs 1 , 2867.Xr kill 1 , 2868.Xr printf 1 , 2869.Xr pwd 1 , 2870.Xr test 1 , 2871.Xr vi 1 , 2872.Xr execve 2 , 2873.Xr getrlimit 2 , 2874.Xr umask 2 , 2875.Xr wctype 3 , 2876.Xr editrc 5 , 2877.Xr shells 5 2878.Sh HISTORY 2879A 2880.Nm 2881command, the Thompson shell, appeared in 2882.At v1 . 2883It was superseded in 2884.At v7 2885by the Bourne shell, which inherited the name 2886.Nm . 2887.Pp 2888This version of 2889.Nm 2890was rewritten in 1989 under the 2891.Bx 2892license after the Bourne shell from 2893.At V.4 . 2894.Sh AUTHORS 2895This version of 2896.Nm 2897was originally written by 2898.An Kenneth Almquist . 2899.Sh BUGS 2900The 2901.Nm 2902utility does not recognize multibyte characters other than UTF-8. 2903Splitting using 2904.Va IFS 2905does not recognize multibyte characters. 2906