bash-hackers-wiki/scripting/bashbehaviour/index.html

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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><link href=https://flokoe.github.io/bash-hackers-wiki/scripting/bashbehaviour/ rel=canonical><link href=../../misc/shell_humor/ rel=prev><link href=../bashchanges/ rel=next><link rel=icon href=../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.5.44"><title>Bash's behaviour - The Bash Hackers Wiki</title><link rel=stylesheet href=../../assets/stylesheets/main.0253249f.min.css><link rel=stylesheet href=../../assets/stylesheets/palette.06af60db.min.css><link rel=preconnect href=https://fonts.gstatic.com crossorigin><link rel=stylesheet href="https://fonts.googleapis.com/css?family=Roboto:300,300i,400,400i,700,700i%7CRoboto+Mono:400,400i,700,700i&display=fallback"><style>:root{--md-text-font:"Roboto";--md-code-font:"Roboto Mono"}</style><script>__md_scope=new 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12.1C428.2 457.8 496 362.9 496 252 496 113.3 383.5 8 244.8 8M97.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </div> <div class=md-source__repository> flokoe/bash-hackers-wiki </div> </a> </div> </nav> </header> <div class=md-container data-md-component=container> <nav class=md-tabs aria-label=Tabs data-md-component=tabs> <div class=md-grid> <ul class=md-tabs__list> <li class=md-tabs__item> <a href=../.. class=md-tabs__link> Start </a> </li> <li class=md-tabs__item> <a href=../../commands/classictest/ class=md-tabs__link> Commands </a> </li> <li class=md-tabs__item> <a href=../../dict/directory/ class=md-tabs__link> Dict </a> </li> <li class=md-tabs__item> <a href=../../howto/calculate-dc/ class=md-tabs__link> Howto </a> </li> <li class=md-tabs__item> <a href=../../internals/shell_options/ class=md-tabs__link> Internals </a> </li> <li class=md-tabs__item> <a href=../../misc/bashphorisms/ class=md-tabs__link> Misc </a> </li> <li class="md-tabs__item md-tabs__item--active"> <a href=./ class=md-tabs__link> Scripting </a> </li> <li class=md-tabs__item> <a href=../../snipplets/ class=md-tabs__link> Snipplets </a> </li> <li class=md-tabs__item> <a href=../../syntax/arith_expr/ class=md-tabs__link> Syntax </a> </li> <li class=md-tabs__item> <a href=../../tags/ class=md-tabs__link> Tags </a> </li> </ul> </div> </nav> <main class=md-main data-md-component=main> <div class="md-main__inner md-grid"> <div class="md-sidebar md-sidebar--primary" data-md-component=sidebar data-md-type=navigation> <div class=md-sidebar__scrollwrap> <div class=md-sidebar__inner> <nav class="md-nav md-nav--primary md-nav--lifted" aria-label=Navigation data-md-level=0> <label 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3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M244.8 8C106.1 8 0 113.3 0 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C428.2 457.8 496 362.9 496 252 496 113.3 383.5 8 244.8 8M97.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </div> <div class=md-source__repository> flokoe/bash-hackers-wiki </div> </a> </div> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../.. class=md-nav__link> <span class=md-ellipsis> Start </span> </a> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_2> <label class=md-nav__link for=__nav_2 id=__nav_2_label tabindex=0> <span class=md-ellipsis> Commands </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=1 aria-labelledby=__nav_2_label aria-expanded=false> <label class=md-nav__title for=__nav_2> <span class="md-nav__icon md-icon"></span> Commands </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../commands/classictest/ class=md-nav__link> <span class=md-ellipsis> The classic test command </span> </a> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_2_2> <label class=md-nav__link for=__nav_2_2 id=__nav_2_2_label tabindex=0> <span class=md-ellipsis> Builtin </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=2 aria-labelledby=__nav_2_2_label aria-expanded=false> <label class=md-nav__title for=__nav_2_2> <span class="md-nav__icon md-icon"></span> Builtin </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../commands/builtin/caller/ class=md-nav__link> <span class=md-ellipsis> The caller builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/cd/ class=md-nav__link> <span class=md-ellipsis> The cd builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/declare/ class=md-nav__link> <span class=md-ellipsis> The declare builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/echo/ class=md-nav__link> <span class=md-ellipsis> The echo builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/eval/ class=md-nav__link> <span class=md-ellipsis> The eval builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/exec/ class=md-nav__link> <span class=md-ellipsis> The exec builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/exit/ class=md-nav__link> <span class=md-ellipsis> The exit builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/export/ class=md-nav__link> <span class=md-ellipsis> The export builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/kill/ class=md-nav__link> <span class=md-ellipsis> The kill builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/let/ class=md-nav__link> <span class=md-ellipsis> The let builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/local/ class=md-nav__link> <span class=md-ellipsis> The local builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/mapfile/ class=md-nav__link> <span class=md-ellipsis> The mapfile builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/printf/ class=md-nav__link> <span class=md-ellipsis> The printf command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/read/ class=md-nav__link> <span class=md-ellipsis> The read builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/readonly/ class=md-nav__link> <span class=md-ellipsis> The readonly builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/return/ class=md-nav__link> <span class=md-ellipsis> The return builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/set/ class=md-nav__link> <span class=md-ellipsis> The set builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/shift/ class=md-nav__link> <span class=md-ellipsis> The shift builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/shopt/ class=md-nav__link> <span class=md-ellipsis> The shopt builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/trap/ class=md-nav__link> <span class=md-ellipsis> The trap builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/unset/ class=md-nav__link> <span class=md-ellipsis> The unset builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/wait/ class=md-nav__link> <span class=md-ellipsis> The wait builtin command </span> </a> </li> </ul> </nav> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_3> <label class=md-nav__link for=__nav_3 id=__nav_3_label tabindex=0> <span class=md-ellipsis> Dict </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=1 aria-labelledby=__nav_3_label aria-expanded=false> <label class=md-nav__title for=__nav_3> <span class="md-nav__icon md-icon"></span> Dict </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../dict/directory/ class=md-nav__link> <span class=md-ellipsis> Directory </span> </a> </li> <li class=md-nav__item> <a href=../../dict/end_of_options/ class=md-nav__link> <span class=md-ellipsis> End of Options </span> </a> </li> <li class=md-nav__item> <a href=../../dict/exit_status/ class=md-nav__link> <span class=md-ellipsis> Exit Status </span> </a> </li> <li class=md-nav__item> <a href=../../dict/file/ class=md-nav__link> <span class=md-ellipsis> File </span> </a> </li> <li class=md-nav__item> <a href=../../dict/filetimes/ class=md-nav__link> <span class=md-ellipsis> File timestamp </span> </a> </li> <li class=md-nav__item> <a href=../../dict/globbing/ class=md-nav__link> <span class=md-ellipsis> Globbing </span> </a> </li> <li class=md-nav__item> <a href=../../dict/hardlink/ class=md-nav__link> <span class=md-ellipsis> Hardlink </span> </a> </li> <li class=md-nav__item> <a href=../../dict/interpreter_directive/ class=md-nav__link> <span class=md-ellipsis> Interpreter Directive </span> </a> </li> <li class=md-nav__item> <a href=../../dict/parameter/ class=md-nav__link> <span class=md-ellipsis> Parameter </span> </a> </li> <li class=md-nav__item> <a href=../../dict/posix/ class=md-nav__link> <span class=md-ellipsis> POSIX </span> </a> </li> <li class=md-nav__item> <a href=../../dict/shell/ class=md-nav__link> <span class=md-ellipsis> Shell </span> </a> </li> <li class=md-nav__item> <a href=../../dict/special_file/ class=md-nav__link> <span class=md-ellipsis> Special file </span> </a> </li> <li class=md-nav__item> <a href=../../dict/symlink/ class=md-nav__link> <span class=md-ellipsis> Symlink </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_4> <label class=md-nav__link for=__nav_4 id=__nav_4_label tabindex=0> <span class=md-ellipsis> Howto </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=1 aria-labelledby=__nav_4_label aria-expanded=false> <label class=md-nav__title for=__nav_4> <span class="md-nav__icon md-icon"></span> Howto </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../howto/calculate-dc/ class=md-nav__link> <span class=md-ellipsis> Calculating with dc </span> </a> </li> <li class=md-nav__item> <a href=../../howto/collapsing_functions/ class=md-nav__link> <span class=md-ellipsis> Collapsing Functions </span> </a> </li> <li class=md-nav__item> <a href=../../howto/conffile/ class=md-nav__link> <span class=md-ellipsis> Config files for your script </span> </a> </li> <li class=md-nav__item> <a href=../../howto/dissectabadoneliner/ class=md-nav__link> <span class=md-ellipsis> Dissect a bad oneliner </span> </a> </li> <li class=md-nav__item> <a href=../../howto/edit-ed/ class=md-nav__link> <span class=md-ellipsis> Editing files via scripts with ed </span> </a> </li> <li class=md-nav__item> <a href=../../howto/getopts_tutorial/ class=md-nav__link> <span class=md-ellipsis> Small getopts tutorial </span> </a> </li> <li class=md-nav__item> <a href=../../howto/mutex/ class=md-nav__link> <span class=md-ellipsis> Lock your script (against parallel execution) </span> </a> </li> <li class=md-nav__item> <a href=../../howto/pax/ class=md-nav__link> <span class=md-ellipsis> pax - the POSIX archiver </span> </a> </li> <li class=md-nav__item> <a href=../../howto/redirection_tutorial/ class=md-nav__link> <span class=md-ellipsis> Illustrated Redirection Tutorial </span> </a> </li> <li class=md-nav__item> <a href=../../howto/testing-your-scripts/ class=md-nav__link> <span class=md-ellipsis> Testing your scripts </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_5> <label class=md-nav__link for=__nav_5 id=__nav_5_label tabindex=0> <span class=md-ellipsis> Internals </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=1 aria-labelledby=__nav_5_label aria-expanded=false> <label class=md-nav__title for=__nav_5> <span class="md-nav__icon md-icon"></span> Internals </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../internals/shell_options/ class=md-nav__link> <span class=md-ellipsis> List of shell options </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_6> <label class=md-nav__link for=__nav_6 id=__nav_6_label tabindex=0> <span class=md-ellipsis> Misc </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=1 aria-labelledby=__nav_6_label aria-expanded=false> <label class=md-nav__title for=__nav_6> <span class="md-nav__icon md-icon"></span> Misc </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../misc/bashphorisms/ class=md-nav__link> <span class=md-ellipsis> The Bashphorisms </span> </a> </li> <li class=md-nav__item> <a href=../../misc/readthesourceluke/ class=md-nav__link> <span class=md-ellipsis> Readthesourceluke </span> </a> </li> <li class=md-nav__item> <a href=../../misc/shell_humor/ class=md-nav__link> <span class=md-ellipsis> Shell Humor </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--active md-nav__item--section md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_7 checked> <label class=md-nav__link for=__nav_7 id=__nav_7_label tabindex> <span class=md-ellipsis> Scripting </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=1 aria-labelledby=__nav_7_label aria-expanded=true> <label class=md-nav__title for=__nav_7> <span class="md-nav__icon md-icon"></span> Scripting </label> <ul class=md-nav__list data-md-scrollfix> <li class="md-nav__item md-nav__item--active"> <input class="md-nav__toggle md-toggle" type=checkbox id=__toc> <label class="md-nav__link md-nav__link--active" for=__toc> <span class=md-ellipsis> Bash's behaviour </span> <span class="md-nav__icon md-icon"></span> </label> <a href=./ class="md-nav__link md-nav__link--active"> <span class=md-ellipsis> Bash's behaviour </span> </a> <nav class="md-nav md-nav--secondary" aria-label="Table of contents"> <label class=md-nav__title for=__toc> <span class="md-nav__icon md-icon"></span> Table of contents </label> <ul class=md-nav__list data-md-component=toc data-md-scrollfix> <li class=md-nav__item> <a href=#bash-startup-modes class=md-nav__link> <span class=md-ellipsis> Bash startup modes </span> </a> <nav class=md-nav aria-label="Bash startup modes"> <ul class=md-nav__list> <li class=md-nav__item> <a href=#login-shell class=md-nav__link> <span class=md-ellipsis> Login shell </span> </a> </li> <li class=md-nav__item> <a href=#interactive-shell class=md-nav__link> <span class=md-ellipsis> Interactive shell </span> </a> </li> <li class=md-nav__item> <a href=#sh-mode class=md-nav__link> <span class=md-ellipsis> SH mode </span> </a> </li> <li class=md-nav__item> <a href=#posix-mode class=md-nav__link> <span class=md-ellipsis> POSIX mode </span> </a> </li> <li class=md-nav__item> <a href=#quick-startup-file-reference class=md-nav__link> <span class=md-ellipsis> Quick startup file reference </span> </a> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=#bash-run-modes class=md-nav__link> <span class=md-ellipsis> Bash run modes </span> </a> <nav class=md-nav aria-label="Bash run modes"> <ul class=md-nav__list> <li class=md-nav__item> <a href=#normal-bash class=md-nav__link> <span class=md-ellipsis> Normal Bash </span> </a> </li> <li class=md-nav__item> <a href=#posix-run-mode class=md-nav__link> <span class=md-ellipsis> POSIX run mode </span> </a> </li> <li class=md-nav__item> <a href=#restricted-shell class=md-nav__link> <span class=md-ellipsis> Restricted shell </span> </a> </li> </ul> </nav> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=../bashchanges/ class=md-nav__link> <span class=md-ellipsis> Bash changes </span> </a> </li> <li class=md-nav__item> <a href=../basics/ class=md-nav__link> <span class=md-ellipsis> The basics of shell scripting </span> </a> </li> <li class=md-nav__item> <a href=../debuggingtips/ class=md-nav__link> <span class=md-ellipsis> Debugging a script </span> </a> </li> <li class=md-nav__item> <a href=../newbie_traps/ class=md-nav__link> <span class=md-ellipsis> Beginner Mistakes </span> </a> </li> <li class=md-nav__item> <a href=../nonportable/ class=md-nav__link> <span class=md-ellipsis> Portability talk </span> </a> </li> <li class=md-nav__item> <a href=../obsolete/ class=md-nav__link> <span class=md-ellipsis> Obsolete and deprecated syntax </span> </a> </li> <li class=md-nav__item> <a href=../posparams/ class=md-nav__link> <span class=md-ellipsis> Handling positional parameters </span> </a> </li> <li class=md-nav__item> <a href=../processtree/ class=md-nav__link> <span class=md-ellipsis> Bash and the process tree </span> </a> </li> <li class=md-nav__item> <a href=../style/ class=md-nav__link> <span class=md-ellipsis> Scripting with style </span> </a> </li> <li class=md-nav__item> <a href=../terminalcodes/ class=md-nav__link> <span class=md-ellipsis> Terminal codes (ANSI/VT100) introduction </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_8> <label class=md-nav__link for=__nav_8 id=__nav_8_label tabindex=0> <span class=md-ellipsis> Snipplets </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=1 aria-labelledby=__nav_8_label aria-expanded=false> <label class=md-nav__title for=__nav_8> <span class="md-nav__icon md-icon"></span> Snipplets </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../snipplets/ class=md-nav__link> <span class=md-ellipsis> Small code snipplets </span> </a> </li> <li class=md-nav__item> <a href=../../snipplets/add_color_to_your_scripts/ class=md-nav__link> <span class=md-ellipsis> Add Color to your scripts </span> </a> </li> <li class=md-nav__item> <a href=../../snipplets/awkcsv/ class=md-nav__link> <span class=md-ellipsis> Using awk to deal with CSV that uses quoted/unquoted delimiters </span> </a> </li> <li class=md-nav__item> <a href=../../snipplets/filesize/ class=md-nav__link> <span class=md-ellipsis> Show size of a file </span> </a> </li> <li class=md-nav__item> <a href=../../snipplets/kill_bg_job_without_message/ class=md-nav__link> <span class=md-ellipsis> Kill a background job without a message </span> </a> </li> <li class=md-nav__item> <a href=../../snipplets/largestfile/ class=md-nav__link> <span class=md-ellipsis> Get largest file </span> </a> </li> <li class=md-nav__item> <a href=../../snipplets/pause_command/ class=md-nav__link> <span class=md-ellipsis> Pausing a script (like MSDOS pause command) </span> </a> </li> <li class=md-nav__item> <a href=../../snipplets/prargs/ class=md-nav__link> <span class=md-ellipsis> Print argument list for testing </span> </a> </li> <li class=md-nav__item> <a href=../../snipplets/print_horizontal_line/ class=md-nav__link> <span class=md-ellipsis> Print a horizontal line </span> </a> </li> <li class=md-nav__item> <a href=../../snipplets/rndstr/ class=md-nav__link> <span class=md-ellipsis> Print a random string or select random elements </span> </a> </li> <li class=md-nav__item> <a href=../../snipplets/screen_saverestore/ class=md-nav__link> <span class=md-ellipsis> Save and restore terminal/screen content </span> </a> </li> <li class=md-nav__item> <a href=../../snipplets/ssh_fetchkeys/ class=md-nav__link> <span class=md-ellipsis> Fetching SSH hostkeys without interaction </span> </a> </li> <li class=md-nav__item> <a href=../../snipplets/ssh_local_var/ class=md-nav__link> <span class=md-ellipsis> Run some bash commands with SSH remotely using local variables </span> </a> </li> <li class=md-nav__item> <a href=../../snipplets/wrapperargs/ class=md-nav__link> <span class=md-ellipsis> Generate code with own arguments properly quoted </span> </a> </li> <li class=md-nav__item> <a href=../../snipplets/xclip/ class=md-nav__link> <span class=md-ellipsis> X-Clipboard on Commandline </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_9> <label class=md-nav__link for=__nav_9 id=__nav_9_label tabindex=0> <span class=md-ellipsis> Syntax </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=1 aria-labelledby=__nav_9_label aria-expanded=false> <label class=md-nav__title for=__nav_9> <span class="md-nav__icon md-icon"></span> Syntax </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../syntax/arith_expr/ class=md-nav__link> <span class=md-ellipsis> Arithmetic expressions </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/arrays/ class=md-nav__link> <span class=md-ellipsis> Arrays </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/basicgrammar/ class=md-nav__link> <span class=md-ellipsis> Basic grammar rules of Bash </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/pattern/ class=md-nav__link> <span class=md-ellipsis> Patterns and pattern matching </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/pe/ class=md-nav__link> <span class=md-ellipsis> Parameter expansion </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/quoting/ class=md-nav__link> <span class=md-ellipsis> Quotes and escaping </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/redirection/ class=md-nav__link> <span class=md-ellipsis> Redirection </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/shellvars/ class=md-nav__link> <span class=md-ellipsis> Special parameters and shell variables </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/words/ class=md-nav__link> <span class=md-ellipsis> Words... </span> </a> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_9_10> <label class=md-nav__link for=__nav_9_10 id=__nav_9_10_label tabindex=0> <span class=md-ellipsis> Ccmd </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=2 aria-labelledby=__nav_9_10_label aria-expanded=false> <label class=md-nav__title for=__nav_9_10> <span class="md-nav__icon md-icon"></span> Ccmd </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../syntax/ccmd/arithmetic_eval/ class=md-nav__link> <span class=md-ellipsis> Arithmetic evaluation (command) </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/ccmd/c_for/ class=md-nav__link> <span class=md-ellipsis> The C-style for-loop </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/ccmd/case/ class=md-nav__link> <span class=md-ellipsis> The case statement </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/ccmd/classic_for/ class=md-nav__link> <span class=md-ellipsis> The classic for-loop </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/ccmd/conditional_expression/ class=md-nav__link> <span class=md-ellipsis> The conditional expression </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/ccmd/grouping_plain/ class=md-nav__link> <span class=md-ellipsis> Grouping commands </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/ccmd/grouping_subshell/ class=md-nav__link> <span class=md-ellipsis> Grouping commands in a subshell </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/ccmd/if_clause/ class=md-nav__link> <span class=md-ellipsis> The if-clause </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/ccmd/intro/ class=md-nav__link> <span class=md-ellipsis> Bash compound commands </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/ccmd/until_loop/ class=md-nav__link> <span class=md-ellipsis> The until loop </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/ccmd/user_select/ class=md-nav__link> <span class=md-ellipsis> User selections </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/ccmd/while_loop/ class=md-nav__link> <span class=md-ellipsis> The while-loop </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_9_11> <label class=md-nav__link for=__nav_9_11 id=__nav_9_11_label tabindex=0> <span class=md-ellipsis> Expansion </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=2 aria-labelledby=__nav_9_11_label aria-expanded=false> <label class=md-nav__title for=__nav_9_11> <span class="md-nav__icon md-icon"></span> Expansion </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../syntax/expansion/arith/ class=md-nav__link> <span class=md-ellipsis> Arithmetic expansion </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/expansion/brace/ class=md-nav__link> <span class=md-ellipsis> Brace expansion </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/expansion/cmdsubst/ class=md-nav__link> <span class=md-ellipsis> Command substitution </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/expansion/globs/ class=md-nav__link> <span class=md-ellipsis> Pathname expansion (globbing) </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/expansion/intro/ class=md-nav__link> <span class=md-ellipsis> Expansions and substitutions </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/expansion/proc_subst/ class=md-nav__link> <span class=md-ellipsis> Process substitution </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/expansion/tilde/ class=md-nav__link> <span class=md-ellipsis> Tilde expansion </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/expansion/wordsplit/ class=md-nav__link> <span class=md-ellipsis> Word splitting </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_9_12> <label class=md-nav__link for=__nav_9_12 id=__nav_9_12_label tabindex=0> <span class=md-ellipsis> Grammar </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=2 aria-labelledby=__nav_9_12_label aria-expanded=false> <label class=md-nav__title for=__nav_9_12> <span class="md-nav__icon md-icon"></span> Grammar </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../syntax/grammar/parser_exec/ class=md-nav__link> <span class=md-ellipsis> Parser exec </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_9_13> <label class=md-nav__link for=__nav_9_13 id=__nav_9_13_label tabindex=0> <span class=md-ellipsis> Keywords </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=2 aria-labelledby=__nav_9_13_label aria-expanded=false> <label class=md-nav__title for=__nav_9_13> <span class="md-nav__icon md-icon"></span> Keywords </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../syntax/keywords/coproc/ class=md-nav__link> <span class=md-ellipsis> The coproc keyword </span> </a> </li> </ul> </nav> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=../../tags/ class=md-nav__link> <span class=md-ellipsis> Tags </span> </a> </li> </ul> </nav> </div> </div> </div> <div class="md-sidebar md-sidebar--secondary" data-md-component=sidebar data-md-type=toc> <div class=md-sidebar__scrollwrap> <div class=md-sidebar__inner> <nav class="md-nav md-nav--secondary" aria-label="Table of contents"> <label class=md-nav__title for=__toc> <span class="md-nav__icon md-icon"></span> Table of contents </label> <ul class=md-nav__list data-md-component=toc data-md-scrollfix> <li class=md-nav__item> <a href=#bash-startup-modes class=md-nav__link> <span class=md-ellipsis> Bash startup modes </span> </a> <nav class=md-nav aria-label="Bash startup modes"> <ul class=md-nav__list> <li class=md-nav__item> <a href=#login-shell class=md-nav__link> <span class=md-ellipsis> Login shell </span> </a> </li> <li class=md-nav__item> <a href=#interactive-shell class=md-nav__link> <span class=md-ellipsis> Interactive shell </span> </a> </li> <li class=md-nav__item> <a href=#sh-mode class=md-nav__link> <span class=md-ellipsis> SH mode </span> </a> </li> <li class=md-nav__item> <a href=#posix-mode class=md-nav__link> <span class=md-ellipsis> POSIX mode </span> </a> </li> <li class=md-nav__item> <a href=#quick-startup-file-reference class=md-nav__link> <span class=md-ellipsis> Quick startup file reference </span> </a> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=#bash-run-modes class=md-nav__link> <span class=md-ellipsis> Bash run modes </span> </a> <nav class=md-nav aria-label="Bash run modes"> <ul class=md-nav__list> <li class=md-nav__item> <a href=#normal-bash class=md-nav__link> <span class=md-ellipsis> Normal Bash </span> </a> </li> <li class=md-nav__item> <a href=#posix-run-mode class=md-nav__link> <span class=md-ellipsis> POSIX run mode </span> </a> </li> <li class=md-nav__item> <a href=#restricted-shell class=md-nav__link> <span class=md-ellipsis> Restricted shell </span> </a> </li> </ul> </nav> </li> </ul> </nav> </div> </div> </div> <div class=md-content data-md-component=content> <article class="md-content__inner md-typeset"> <nav class=md-tags> <a href=../../tags/#bash class=md-tag>bash</a> <a href=../../tags/#shell class=md-tag>shell</a> <a href=../../tags/#scripting class=md-tag>scripting</a> <a href=../../tags/#startup class=md-tag>startup</a> <a href=../../tags/#files class=md-tag>files</a> <a href=../../tags/#dotfiles class=md-tag>dotfiles</a> <a href=../../tags/#modes class=md-tag>modes</a> <a href=../../tags/#posix class=md-tag>POSIX</a> </nav> <a href=https://github.com/flokoe/bash-hackers-wiki/edit/main/docs/scripting/bashbehaviour.md title="Edit this page" class="md-content__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 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<h2 id=bash-startup-modes>Bash startup modes<a class=headerlink href=#bash-startup-modes title="Permanent link">&para;</a></h2> <h3 id=login-shell>Login shell<a class=headerlink href=#login-shell title="Permanent link">&para;</a></h3> <p>As a "login shell", Bash reads and sets (executes) the user's profile from <code>/etc/profile</code> and one of <code>~/.bash_profile</code>, <code>~/.bash_login</code>, or <code>~/.profile</code> (in that order, using the first one that's readable!).</p> <p>When a login shell exits, Bash reads and executes commands from the file <code>~/.bash_logout</code>, if it exists.</p> <p>Why an extra login shell mode? There are many actions and variable sets that only make sense for the initial user login. That's why all UNIX&reg; shells have (should have) a "login" mode.</p> <p><u><strong>Methods to start Bash as a login shell:</strong></u></p> <ul> <li>the first character of <code>argv[0]</code> is <code>-</code> (a hyphen): traditional UNIX&reg; shells start from the <code>login</code> binary</li> <li>Bash is started with the <code>-l</code> option</li> <li>Bash is started with the <code>--login</code> option</li> </ul> <p><u><strong>Methods to test for login shell mode:</strong></u></p> <ul> <li>the shell option <code>login_shell</code> is set</li> </ul> <p><u><strong>Related switches:</strong></u></p> <ul> <li><code>--noprofile</code> disables reading of all profile files</li> </ul> <h3 id=interactive-shell>Interactive shell<a class=headerlink href=#interactive-shell title="Permanent link">&para;</a></h3> <p>When Bash starts as an interactive non-login shell, it reads and executes commands from <code>~/.bashrc</code>. This file should contain, for example, aliases, since they need to be defined in every shell as they're not inherited from the parent shell.</p> <p>The feature to have a system-wide <code>/etc/bash.bashrc</code> or a similar system-wide rc-file is specific to vendors and distributors that ship <em>their own, patched variant of Bash</em>. The classic way to have a system-wide rc file is to <code>source /etc/bashrc</code> from every user's <code>~/.bashrc</code>.</p> <p><u><strong>Methods to test for interactive-shell mode:</strong></u></p> <ul> <li>the special parameter <code>$-</code> contains the letter <code>i</code> (lowercase I)</li> </ul> <p><u><strong>Related switches:</strong></u></p> <ul> <li><code>-i</code> forces the interactive mode</li> <li><code>--norc</code> disables reading of the startup files (e.g. <code>/etc/bash.bashrc</code> if supported) and <code>~/.bashrc</code></li> <li><code>--rcfile</code> defines another startup file (instead of <code>/etc/bash.bashrc</code> and <code>~/.bashrc</code>)</li> </ul> <h3 id=sh-mode>SH mode<a class=headerlink href=#sh-mode title="Permanent link">&para;</a></h3> <p>When Bash starts in SH compatiblity mode, it tries to mimic the startup behaviour of historical versions of <code>sh</code> as closely as possible, while conforming to the POSIX&reg; standard as well. The profile files read are <code>/etc/profile</code> and <code>~/.profile</code>, if it's a login shell.</p> <p>If it's not a login shell, the environment variable <a href=../../syntax/shellvars/#ENV>ENV</a> is evaluated and the resulting filename is used as the name of the startup file.</p> <p>After the startup files are read, Bash enters the <a href=#posix_run_mode>POSIX&reg; compatiblity mode (for running, not for starting!)</a>.</p> <p><u><strong>Bash starts in <code>sh</code> compatiblity mode when:</strong></u></p> <ul> <li>the base filename in <code>argv[0]</code> is <code>sh</code> (:!: NB: <code>/bin/sh</code> may be linked to <code>/bin/bash</code>, but that doesn't mean it acts like <code>/bin/bash</code> :!:)</li> </ul> <h3 id=posix-mode>POSIX mode<a class=headerlink href=#posix-mode title="Permanent link">&para;</a></h3> <p>When Bash is started in POSIX&reg; mode, it follows the POSIX&reg; standard for startup files. In this mode, <strong>interactive shells</strong> expand the <a href=../../syntax/shellvars/#ENV>ENV</a> variable and commands are read and executed from the file whose name is the expanded value. No other startup files are read. Hence, a non-interactive shell doesn't read any startup files in POSIX&reg; mode.</p> <p><u><strong>Bash starts in POSIX&reg; mode when:</strong></u></p> <ul> <li>the commandline option <code>--posix</code> is specified</li> <li>the environment variable <a href=../../syntax/shellvars/#POSIXLY_CORRECT>POSIXLY_CORRECT</a> is set</li> </ul> <h3 id=quick-startup-file-reference>Quick startup file reference<a class=headerlink href=#quick-startup-file-reference title="Permanent link">&para;</a></h3> <ul> <li>Eventual system-wide rc-files are usually read when <code>~/.bashrc</code> would be read (at least Debian GNU/Linux behaves like that)</li> <li>Regardless of the system-wide files in <code>/etc</code> which are always read, Bash usually reads the first file found, when multiple choices are given (for user files in <code>~/</code>)</li> </ul> <table> <thead> <tr> <th>Mode</th> <th><code>/etc/profile</code></th> <th><code>~/.bash_profile</code></th> <th><code>~/.bash_login</code></th> <th><code>~/.profile</code></th> <th><code>~/.bashrc</code></th> <th><code>${ENV}</code></th> </tr> </thead> <tbody> <tr> <td>Login shell</td> <td></td> <td></td> <td></td> <td></td> <td>🚫</td> <td>🚫</td> </tr> <tr> <td>Interactive shell</td> <td>🚫</td> <td>🚫</td> <td>🚫</td> <td>🚫</td> <td></td> <td>🚫</td> </tr> <tr> <td>SH compatible login</td> <td></td> <td>🚫</td> <td>🚫</td> <td></td> <td>🚫</td> <td>🚫</td> </tr> <tr> <td>SH compatible</td> <td>🚫</td> <td>🚫</td> <td>🚫</td> <td>🚫</td> <td>🚫</td> <td></td> </tr> <tr> <td>POSIX&reg; compatiblity</td> <td>🚫</td> <td>🚫</td> <td>🚫</td> <td>🚫</td> <td>🚫</td> <td></td> </tr> </tbody> </table> <h2 id=bash-run-modes>Bash run modes<a class=headerlink href=#bash-run-modes title="Permanent link">&para;</a></h2> <h3 id=normal-bash>Normal Bash<a class=headerlink href=#normal-bash title="Permanent link">&para;</a></h3> <h3 id=posix-run-mode>POSIX run mode<a class=headerlink href=#posix-run-mode title="Permanent link">&para;</a></h3> <p>In POSIX&reg; mode, Bash follows the POSIX&reg; standard regarding behaviour and parsing (excerpt from a Bash maintainer's document):</p> <div class=highlight><pre><span></span><code>Starting Bash with the `--posix&#39; command-line option or executing `set
-o posix&#39; while Bash is running will cause Bash to conform more closely
to the POSIX standard by changing the behavior to match that specified
by POSIX in areas where the Bash default differs.
When invoked as `sh&#39;, Bash enters POSIX mode after reading the startup
files.
The following lists what&#39;s changed when Bash is in `POSIX mode&#39;:
1. When a command in the hash table no longer exists, Bash will
re-search `$PATH&#39; to find the new location. This is also
available with `shopt -s checkhash&#39;.
2. The message printed by the job control code and builtins when a job
exits with a non-zero status is `Done(status)&#39;.
3. The message printed by the job control code and builtins when a job
is stopped is `Stopped(SIGNAME)&#39;, where SIGNAME is, for example,
`SIGTSTP&#39;.
4. The `bg&#39; builtin uses the required format to describe each job
placed in the background, which does not include an indication of
whether the job is the current or previous job.
5. Reserved words appearing in a context where reserved words are
recognized do not undergo alias expansion.
6. The POSIX `PS1&#39; and `PS2&#39; expansions of `!&#39; to the history number
and `!!&#39; to `!&#39; are enabled, and parameter expansion is performed
on the values of `PS1&#39; and `PS2&#39; regardless of the setting of the
`promptvars&#39; option.
7. The POSIX startup files are executed (`$ENV&#39;) rather than the
normal Bash files.
8. Tilde expansion is only performed on assignments preceding a
command name, rather than on all assignment statements on the line.
9. The default history file is `~/.sh_history&#39; (this is the default
value of `$HISTFILE&#39;).
10. The output of `kill -l&#39; prints all the signal names on a single
line, separated by spaces, without the `SIG&#39; prefix.
11. The `kill&#39; builtin does not accept signal names with a `SIG&#39;
prefix.
12. Non-interactive shells exit if FILENAME in `.&#39; FILENAME is not
found.
13. Non-interactive shells exit if a syntax error in an arithmetic
expansion results in an invalid expression.
14. Redirection operators do not perform filename expansion on the word
in the redirection unless the shell is interactive.
15. Redirection operators do not perform word splitting on the word in
the redirection.
16. Function names must be valid shell names. That is, they may not
contain characters other than letters, digits, and underscores, and
may not start with a digit. Declaring a function with an invalid
name causes a fatal syntax error in non-interactive shells.
17. POSIX special builtins are found before shell functions during
command lookup.
18. If a POSIX special builtin returns an error status, a
non-interactive shell exits. The fatal errors are those listed in
the POSIX standard, and include things like passing incorrect
options, redirection errors, variable assignment errors for
assignments preceding the command name, etc.
19. If `CDPATH&#39; is set, the `cd&#39; builtin will not implicitly append
the current directory to it. This means that `cd&#39; will fail if no
valid directory name can be constructed from any of the entries in
`$CDPATH&#39;, even if the a directory with the same name as the name
given as an argument to `cd&#39; exists in the current directory.
20. A non-interactive shell exits with an error status if a variable
assignment error occurs when no command name follows the assignment
statements. A variable assignment error occurs, for example, when
trying to assign a value to a readonly variable.
21. A non-interactive shell exits with an error status if the iteration
variable in a `for&#39; statement or the selection variable in a
`select&#39; statement is a readonly variable.
22. Process substitution is not available.
23. Assignment statements preceding POSIX special builtins persist in
the shell environment after the builtin completes.
24. Assignment statements preceding shell function calls persist in the
shell environment after the function returns, as if a POSIX
special builtin command had been executed.
25. The `export&#39; and `readonly&#39; builtin commands display their output
in the format required by POSIX.
26. The `trap&#39; builtin displays signal names without the leading `SIG&#39;.
27. The `trap&#39; builtin doesn&#39;t check the first argument for a possible
signal specification and revert the signal handling to the original
disposition if it is, unless that argument consists solely of
digits and is a valid signal number. If users want to reset the
handler for a given signal to the original disposition, they
should use `-&#39; as the first argument.
28. The `.&#39; and `source&#39; builtins do not search the current directory
for the filename argument if it is not found by searching `PATH&#39;.
29. Subshells spawned to execute command substitutions inherit the
value of the `-e&#39; option from the parent shell. When not in POSIX
mode, Bash clears the `-e&#39; option in such subshells.
30. Alias expansion is always enabled, even in non-interactive shells.
31. When the `alias&#39; builtin displays alias definitions, it does not
display them with a leading `alias &#39; unless the `-p&#39; option is
supplied.
32. When the `set&#39; builtin is invoked without options, it does not
display shell function names and definitions.
33. When the `set&#39; builtin is invoked without options, it displays
variable values without quotes, unless they contain shell
metacharacters, even if the result contains nonprinting characters.
34. When the `cd&#39; builtin is invoked in LOGICAL mode, and the pathname
constructed from `$PWD&#39; and the directory name supplied as an
argument does not refer to an existing directory, `cd&#39; will fail
instead of falling back to PHYSICAL mode.
35. When the `pwd&#39; builtin is supplied the `-P&#39; option, it resets
`$PWD&#39; to a pathname containing no symlinks.
36. The `pwd&#39; builtin verifies that the value it prints is the same as
the current directory, even if it is not asked to check the file
system with the `-P&#39; option.
37. When listing the history, the `fc&#39; builtin does not include an
indication of whether or not a history entry has been modified.
38. The default editor used by `fc&#39; is `ed&#39;.
39. The `type&#39; and `command&#39; builtins will not report a non-executable
file as having been found, though the shell will attempt to
execute such a file if it is the only so-named file found in
`$PATH&#39;.
40. The `vi&#39; editing mode will invoke the `vi&#39; editor directly when
the `v&#39; command is run, instead of checking `$FCEDIT&#39; and
`$EDITOR&#39;.
41. When the `xpg_echo&#39; option is enabled, Bash does not attempt to
interpret any arguments to `echo&#39; as options. Each argument is
displayed, after escape characters are converted.
There is other POSIX behavior that Bash does not implement by default
even when in POSIX mode. Specifically:
1. The `fc&#39; builtin checks `$EDITOR&#39; as a program to edit history
entries if `FCEDIT&#39; is unset, rather than defaulting directly to
`ed&#39;. `fc&#39; uses `ed&#39; if `EDITOR&#39; is unset.
2. As noted above, Bash requires the `xpg_echo&#39; option to be enabled
for the `echo&#39; builtin to be fully conformant.
Bash can be configured to be POSIX-conformant by default, by specifying
the `--enable-strict-posix-default&#39; to `configure&#39; when building.
</code></pre></div> <div class="admonition warning"> <p class=admonition-title>FIXME</p> <p>help me to find out what breaks in POSIX&reg; mode!</p> </div> <p><u><strong>The POSIX&reg; mode can be switched on by:</strong></u></p> <ul> <li>Bash starting as <code>sh</code> (the basename of <code>argv[0]</code> is <code>sh</code>)</li> <li>starting Bash with the commandline option <code>--posix</code></li> <li>on startup, the environment variable <a href=../../syntax/shellvars/#POSIXLY_CORRECT>POSIXLY_CORRECT</a> is set</li> <li>the command <code>set -o posix</code></li> </ul> <p><u><strong>Tests for the POSIX&reg; mode:</strong></u></p> <ul> <li>the variable <a href=../../syntax/shellvars/#SHELLOPTS>SHELLOPTS</a> contains <code>posix</code> in its list</li> </ul> <h3 id=restricted-shell>Restricted shell<a class=headerlink href=#restricted-shell title="Permanent link">&para;</a></h3> <p>In restricted mode, Bash sets up (and runs) a shell environment that's far more controlled and limited than the standard shell mode. It acts like normal Bash with the following restrictions:</p> <ul> <li>the <code>cd</code> command can't be used to change directories</li> <li>the variables <a href=../../syntax/shellvars/#SHELL>SHELL</a>, <a href=../../syntax/shellvars/#PATH>PATH</a>, <a href=../../syntax/shellvars/#ENV>ENV</a> and <a href=../../syntax/shellvars/#BASH_ENV>BASH_ENV</a> can't be set or unset</li> <li>command names that contain a <code>/</code> (slash) can't be called (hence you're limited to <code>PATH</code>)</li> <li>filenames containing a <code>/</code> (slash) can't be specified as argument to the <code>source</code> or <code>.</code> builtin command</li> <li>filenames containing a <code>/</code> (slash) can't be specified as argument to the <code>-p</code> option of the <code>hash</code> builtin command</li> <li>function definitions are not inherited from the environment at shell startup</li> <li>the environment variable <a href=../../syntax/shellvars/#SHELLOPTS>SHELLOPTS</a> is ignored at startup</li> <li>redirecting output using the <code>&gt;</code>, <code>&gt;|</code>, <code>&lt;&gt;</code>, <code>&gt;&amp;</code>, <code>&amp;&gt;</code>, and <code>&gt;&gt;</code> redirection operators isn't allowed</li> <li>the <code>exec</code> builtin command can't replace the shell with another process</li> <li>adding or deleting builtin commands with the <code>-f</code> and <code>-d</code> options to the enable builtin command is forbidden</li> <li>using the <code>enable</code> builtin command to enable disabled shell builtins doesn't work</li> <li>the <code>-p</code> option to the <code>command</code> builtin command doesn't work</li> <li>turning off restricted mode with <code>set +r</code> or <code>set +o restricted</code> is (of course) forbidden</li> </ul> <p>The "-r" restrictions are turned on <strong>after</strong> Bash has read its startup files.</p> <p>When the command that is run is a shell script, then the restrictions are <strong>turned off</strong> for the (sub-)shell that runs that shell script.</p> <p><u><strong>The restricted shell can be switched on by:</strong></u></p> <ul> <li>calling Bash as <code>rbash</code> (the basename of <code>argv[0]</code> is <code>rbash</code>)</li> <li>calling Bash with the <code>-r</code> option</li> <li>calling Bash with the <code>--restricted</code> option</li> </ul> <p><u><strong>Tests for restricted mode:</strong></u></p> <ul> <li>the special parameter <code>$-</code> contains the letter <code>r</code> (lowercase R)</li> <li>the shell option <code>restricted_shell</code> is set and can be checked by the <code>shopt</code> builtin command</li> </ul> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date">November 13, 2024</span> </span> <span class=md-source-file__fact> <span class=md-icon title=Created> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M14.47 15.08 11 13V7h1.5v5.25l3.08 1.83c-.41.28-.79.62-1.11 1m-1.39 4.84c-.36.05-.71.08-1.08.08-4.42 0-8-3.58-8-8s3.58-8 8-8 8 3.58 8 8c0 .37-.03.72-.08 1.08.69.1 1.33.32 1.92.64.1-.56.16-1.13.16-1.72 0-5.5-4.5-10-10-10S2 6.5 2 12s4.47 10 10 10c.59 0 1.16-.06 1.72-.16-.32-.59-.54-1.23-.64-1.92M18 15v3h-3v2h3v3h2v-3h3v-2h-3v-3z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date">November 13, 2024</span> </span> </aside> <h2 id=__comments>Comments</h2> <script src=https://giscus.app/client.js data-repo=flokoe/bash-hackers-wiki data-repo-id=R_kgDOJ3Nr6Q data-category="Giscus Page Comments" data-category-id=DIC_kwDOJ3Nr6c4CXq9t data-mapping=pathname data-strict=1 data-reactions-enabled=1 data-emit-metadata=0 data-input-position=top data-theme=preferred_color_scheme data-lang=en data-loading=lazy crossorigin=anonymous async>
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