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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--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_7> <label class=md-nav__link for=__nav_7 id=__nav_7_label tabindex=0> <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=false> <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> <a href=../../scripting/bashbehaviour/ class=md-nav__link> <span class=md-ellipsis> Bash's behaviour </span> </a> </li> <li class=md-nav__item> <a href=../../scripting/bashchanges/ class=md-nav__link> <span class=md-ellipsis> Bash changes </span> </a> </li> <li class=md-nav__item> <a href=../../scripting/basics/ class=md-nav__link> <span class=md-ellipsis> The basics of shell scripting </span> </a> </li> <li class=md-nav__item> <a href=../../scripting/debuggingtips/ class=md-nav__link> <span class=md-ellipsis> Debugging a script </span> </a> </li> <li class=md-nav__item> <a href=../../scripting/newbie_traps/ class=md-nav__link> <span class=md-ellipsis> Beginner Mistakes </span> </a> </li> <li class=md-nav__item> <a href=../../scripting/nonportable/ class=md-nav__link> <span class=md-ellipsis> Portability talk </span> </a> </li> <li class=md-nav__item> <a href=../../scripting/obsolete/ class=md-nav__link> <span class=md-ellipsis> Obsolete and deprecated syntax </span> </a> </li> <li class=md-nav__item> <a href=../../scripting/posparams/ class=md-nav__link> <span class=md-ellipsis> Handling positional parameters </span> </a> </li> <li class=md-nav__item> <a href=../../scripting/processtree/ class=md-nav__link> <span class=md-ellipsis> Bash and the process tree </span> </a> </li> <li class=md-nav__item> <a href=../../scripting/style/ class=md-nav__link> <span class=md-ellipsis> Scripting with style </span> </a> </li> <li class=md-nav__item> <a href=../../scripting/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--active md-nav__item--section md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_9 checked> <label class=md-nav__link for=__nav_9 id=__nav_9_label tabindex> <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=true> <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=../arith_expr/ class=md-nav__link> <span class=md-ellipsis> Arithmetic expressions </span> </a> </li> <li class=md-nav__item> <a href=../arrays/ class=md-nav__link> <span class=md-ellipsis> Arrays </span> </a> </li> <li class=md-nav__item> <a href=../basicgrammar/ class=md-nav__link> <span class=md-ellipsis> Basic grammar rules of Bash </span> </a> </li> <li class=md-nav__item> <a href=../pattern/ class=md-nav__link> <span class=md-ellipsis> Patterns and pattern matching </span> </a> </li> <li class=md-nav__item> <a href=../pe/ class=md-nav__link> <span class=md-ellipsis> Parameter expansion </span> </a> </li> <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> Quotes and escaping </span> <span class="md-nav__icon md-icon"></span> </label> <a href=./ class="md-nav__link md-nav__link--active"> <span class=md-ellipsis> Quotes and escaping </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=#per-character-escaping class=md-nav__link> <span class=md-ellipsis> Per-character escaping </span> </a> </li> <li class=md-nav__item> <a href=#weak-quoting class=md-nav__link> <span class=md-ellipsis> Weak quoting </span> </a> </li> <li class=md-nav__item> <a href=#strong-quoting class=md-nav__link> <span class=md-ellipsis> Strong quoting </span> </a> </li> <li class=md-nav__item> <a href=#ansi-c-like-strings class=md-nav__link> <span class=md-ellipsis> ANSI C like strings </span> </a> </li> <li class=md-nav__item> <a href=#i18nl10n class=md-nav__link> <span class=md-ellipsis> I18N/L10N </span> </a> </li> <li class=md-nav__item> <a href=#common-mistakes class=md-nav__link> <span class=md-ellipsis> Common mistakes </span> </a> <nav class=md-nav aria-label="Common mistakes"> <ul class=md-nav__list> <li class=md-nav__item> <a href=#string-lists-in-for-loops class=md-nav__link> <span class=md-ellipsis> String lists in for-loops </span> </a> </li> <li class=md-nav__item> <a href=#working-out-the-test-command class=md-nav__link> <span class=md-ellipsis> Working out the test-command </span> </a> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=#see-also class=md-nav__link> <span class=md-ellipsis> See also </span> </a> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=../redirection/ class=md-nav__link> <span class=md-ellipsis> Redirection </span> </a> </li> <li class=md-nav__item> <a href=../shellvars/ class=md-nav__link> <span class=md-ellipsis> Special parameters and shell variables </span> </a> </li> <li class=md-nav__item> <a href=../words/ class=md-nav__link> <span class=md-ellipsis> Words... </span> </a> </li> <li class="md-nav__item md-nav__item--section 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> <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=../ccmd/arithmetic_eval/ class=md-nav__link> <span class=md-ellipsis> Arithmetic evaluation (command) </span> </a> </li> <li class=md-nav__item> <a href=../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=../ccmd/case/ class=md-nav__link> <span class=md-ellipsis> The case statement </span> </a> </li> <li class=md-nav__item> <a href=../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=../ccmd/conditional_expression/ class=md-nav__link> <span class=md-ellipsis> The conditional expression </span> </a> </li> <li class=md-nav__item> <a href=../ccmd/grouping_plain/ class=md-nav__link> <span class=md-ellipsis> Grouping commands </span> </a> </li> <li class=md-nav__item> <a href=../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=../ccmd/if_clause/ class=md-nav__link> <span class=md-ellipsis> The if-clause </span> </a> </li> <li class=md-nav__item> <a href=../ccmd/intro/ class=md-nav__link> <span class=md-ellipsis> Bash compound commands </span> </a> </li> <li class=md-nav__item> <a href=../ccmd/until_loop/ class=md-nav__link> <span class=md-ellipsis> The until loop </span> </a> </li> <li class=md-nav__item> <a href=../ccmd/user_select/ class=md-nav__link> <span class=md-ellipsis> User selections </span> </a> </li> <li class=md-nav__item> <a href=../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--section 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> <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=../expansion/arith/ class=md-nav__link> <span class=md-ellipsis> Arithmetic expansion </span> </a> </li> <li class=md-nav__item> <a href=../expansion/brace/ class=md-nav__link> <span class=md-ellipsis> Brace expansion </span> </a> </li> <li class=md-nav__item> <a href=../expansion/cmdsubst/ class=md-nav__link> <span class=md-ellipsis> Command substitution </span> </a> </li> <li class=md-nav__item> <a href=../expansion/globs/ class=md-nav__link> <span class=md-ellipsis> Pathname expansion (globbing) </span> </a> </li> <li class=md-nav__item> <a href=../expansion/intro/ class=md-nav__link> <span class=md-ellipsis> Expansions and substitutions </span> </a> </li> <li class=md-nav__item> <a href=../expansion/proc_subst/ class=md-nav__link> <span class=md-ellipsis> Process substitution </span> </a> </li> <li class=md-nav__item> <a href=../expansion/tilde/ class=md-nav__link> <span class=md-ellipsis> Tilde expansion </span> </a> </li> <li class=md-nav__item> <a href=../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--section 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> <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=../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--section 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> <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=../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=#per-character-escaping class=md-nav__link> <span class=md-ellipsis> Per-character escaping </span> </a> </li> <li class=md-nav__item> <a href=#weak-quoting class=md-nav__link> <span class=md-ellipsis> Weak quoting </span> </a> </li> <li class=md-nav__item> <a href=#strong-quoting class=md-nav__link> <span class=md-ellipsis> Strong quoting </span> </a> </li> <li class=md-nav__item> <a href=#ansi-c-like-strings class=md-nav__link> <span class=md-ellipsis> ANSI C like strings </span> </a> </li> <li class=md-nav__item> <a href=#i18nl10n class=md-nav__link> <span class=md-ellipsis> I18N/L10N </span> </a> </li> <li class=md-nav__item> <a href=#common-mistakes class=md-nav__link> <span class=md-ellipsis> Common mistakes </span> </a> <nav class=md-nav aria-label="Common mistakes"> <ul class=md-nav__list> <li class=md-nav__item> <a href=#string-lists-in-for-loops class=md-nav__link> <span class=md-ellipsis> String lists in for-loops </span> </a> </li> <li class=md-nav__item> <a href=#working-out-the-test-command class=md-nav__link> <span class=md-ellipsis> Working out the test-command </span> </a> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=#see-also class=md-nav__link> <span class=md-ellipsis> See also </span> </a> </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/#quoting class=md-tag>quoting</a> <a href=../../tags/#quotes class=md-tag>quotes</a> <a href=../../tags/#escape class=md-tag>escape</a> <a href=../../tags/#backslash class=md-tag>backslash</a> <a href=../../tags/#marks class=md-tag>marks</a> <a href=../../tags/#singlequotes class=md-tag>singlequotes</a> <a href=../../tags/#doublequotes class=md-tag>doublequotes</a> <a href=../../tags/#single class=md-tag>single</a> <a href=../../tags/#double class=md-tag>double</a> </nav> <a href=https://github.com/flokoe/bash-hackers-wiki/edit/main/docs/syntax/quoting.md title="Edit this page" class="md-content__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M10 20H6V4h7v5h5v3.1l2-2V8l-6-6H6c-1.1 0-2 .9-2 2v16c0 1.1.9 2 2 2h4zm10.2-7c.1 0 .3.1.4.2l1.3 1.3c.2.2.2.6 0 .8l-1 1-2.1-2.1 1-1c.1-.1.2-.2.4-.2m0 3.9L14.1 23H12v-2.1l6.1-6.1z"/></svg> </a> <a href=https://github.com/flokoe/bash-hackers-wiki/raw/main/docs/syntax/quoting.md title="View source of this page" class="md-content__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M17 18c.56 0 1 .44 1 1s-.44 1-1 1-1-.44-1-1 .44-1 1-1m0-3c-2.73 0-5.06 1.66-6 4 .94 2.34 3.27 4 6 4s5.06-1.66 6-4c-.94-2.34-3.27-4-6-4m0 6.5a2.5 2.5 0 0 1-2.5-2.5 2.5 2.5 0 0 1 2.5-2.5 2.5 2.5 0 0 1 2.5 2.5 2.5 2.5 0 0 1-2.5 2.5M9.27 20H6V4h7v5h5v4.07c.7.08 1.36.25 2 .49V8l-6-6H6a2 2 0 0 0-2 2v16a2 2 0 0 0 2 2h4.5a8.2 8.2 0 0 1-1.23-2"/></svg> </a> <h1 id=quotes-and-escaping>Quotes and escaping<a class=headerlink href=#quotes-and-escaping title="Permanent link">¶</a></h1> <p>Quoting and escaping are important, as they influence the way Bash acts upon your input. There are three recognized types:</p> <ul> <li><strong>per-character escaping</strong> using a backslash: <code>\$stuff</code></li> <li><strong>weak quoting</strong> with double-quotes: <code>"stuff"</code></li> <li><strong>strong quoting</strong> with single-quotes: <code>'stuff'</code></li> </ul> <p>All three forms have the very same purpose: <strong>They give you general control over parsing, expansion and expansion results.</strong></p> <p>Besides these basic variants, there are some special quoting methods (like interpreting ANSI-C escapes in a string) you'll meet below.</p> <p>:!: <strong>ATTENTION</strong> :!: The quote characters (<code>"</code>, double quote and <code>'</code>, single quote) are a syntax element that influence parsing. It is not related to the quote characters passed as text to the command line! The syntax quotes are removed before the command is called! Example:</p> <div class=highlight><pre><span></span><code>### NO NO NO: this passes three strings:
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### (1) "my
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### (2) multiword
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### (3) argument"
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MYARG="\"my multiword argument\""
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somecommand $MYARG
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### THIS IS NOT (!) THE SAME AS ###
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command "my multiword argument"
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### YOU NEED ###
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MYARG="my multiword argument"
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command "$MYARG"
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</code></pre></div> <h2 id=per-character-escaping>Per-character escaping<a class=headerlink href=#per-character-escaping title="Permanent link">¶</a></h2> <p>Per-character escaping is useful in on expansions and substitutions. In general, a character that has a special meaning to Bash, like the dollar-sign (<code>$</code>) can be masked to not have a special meaning using the backslash:</p> <div class=highlight><pre><span></span><code>echo \$HOME is set to \"$HOME\"
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|
</code></pre></div> <ul> <li><code>\$HOME</code> won't expand because it's not in variable-expansion syntax anymore</li> <li>The backslash changes the quotes into literals - otherwise Bash would interpret them</li> </ul> <p>The sequence <code><newline></code> (an unquoted backslash, followed by a <code><newline></code> character) is interpreted as <strong>line continuation</strong>. It is removed from the input stream and thus effectively ignored. Use it to beautify your code:</p> <div class=highlight><pre><span></span><code># escapestr_sed()
|
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# read a stream from stdin and escape characters in text that could be interpreted as
|
|
# special characters by sed
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escape_sed() {
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sed \
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-e 's/\//\\\//g' \
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-e 's/\&/\\\&/g'
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}
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</code></pre></div> <p>The backslash can be used to mask every character that has a special meaning to bash. <u>Exception:</u> Inside a single-quoted string (see below).</p> <h2 id=weak-quoting>Weak quoting<a class=headerlink href=#weak-quoting title="Permanent link">¶</a></h2> <p>Inside a weak-quoted string there's <strong>no special interpretion of</strong>:</p> <ul> <li>spaces as word-separators (on inital command line splitting and on <a href=../expansion/wordsplit/ >word splitting</a>!)</li> <li>single-quotes to introduce strong-quoting (see below)</li> <li>characters for pattern matching</li> <li>tilde expansion</li> <li>pathname expansion</li> <li>process substitution</li> </ul> <p>Everything else, especially <a href=../pe/ >parameter expansion</a>, is performed!</p> <div class=highlight><pre><span></span><code>ls -l "*"
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|
</code></pre></div> <p>Will not be expanded. <code>ls</code> gets the literal <code>*</code> as argument. It will, unless you have a file named <code>*</code>, spit out an error.</p> <div class=highlight><pre><span></span><code>echo "Your PATH is: $PATH"
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|
</code></pre></div> <p>Will work as expected. <code>$PATH</code> is expanded, because it's double (weak) quoted.</p> <p>If a backslash in double quotes ("weak quoting") occurs, there are 2 ways to deal with it</p> <ul> <li>if the baskslash is followed by a character that would have a special meaning even inside double-quotes, the backslash is removed and the following character looses its special meaning</li> <li>if the backslash is followed by a character without special meaning, the backslash is not removed</li> </ul> <p>In particuar this means that <code>"\$"</code> will become <code>$</code>, but <code>"\x"</code> will become <code>\x</code>.</p> <h2 id=strong-quoting>Strong quoting<a class=headerlink href=#strong-quoting title="Permanent link">¶</a></h2> <p>Strong quoting is very easy to explain:</p> <p>Inside a single-quoted string <strong>nothing</strong> is interpreted, except the single-quote that closes the string.</p> <div class=highlight><pre><span></span><code>echo 'Your PATH is: $PATH'
|
|
</code></pre></div> <p><code>$PATH</code> won't be expanded, it's interpreted as ordinary text because it's surrounded by strong quotes.</p> <p>In practise that means, to produce a text like <code>Here's my test...</code> as a single-quoted string, you have to leave and re-enter the single quoting to get the character "<code>'</code>" as literal text:</p> <div class=highlight><pre><span></span><code># WRONG
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echo 'Here's my test...'
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|
|
|
# RIGHT
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echo 'Here'\''s my test...'
|
|
|
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# ALTERNATIVE: It's also possible to mix-and-match quotes for readability:
|
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echo "Here's my test"
|
|
</code></pre></div> <h2 id=ansi-c-like-strings>ANSI C like strings<a class=headerlink href=#ansi-c-like-strings title="Permanent link">¶</a></h2> <p>Bash provides another quoting mechanism: Strings that contain ANSI C-like escape sequences. The Syntax is:</p> <div class=highlight><pre><span></span><code>$'string'
|
|
</code></pre></div> <p>where the following escape sequences are decoded in <code>string</code>:</p> <table> <thead> <tr> <th>Code</th> <th>Meaning</th> </tr> </thead> <tbody> <tr> <td><code>\"</code></td> <td>double-quote</td> </tr> <tr> <td><code>\'</code></td> <td>single-quote</td> </tr> <tr> <td><code>\\</code></td> <td>backslash</td> </tr> <tr> <td><code>\a</code></td> <td>terminal alert character (bell)</td> </tr> <tr> <td><code>\b</code></td> <td>backspace</td> </tr> <tr> <td><code>\e</code></td> <td>escape (ASCII 033)</td> </tr> <tr> <td><code>\E</code></td> <td>escape (ASCII 033) <strong>\E is non-standard</strong></td> </tr> <tr> <td><code>\f</code></td> <td>form feed</td> </tr> <tr> <td><code>\n</code></td> <td>newline</td> </tr> <tr> <td><code>\r</code></td> <td>carriage return</td> </tr> <tr> <td><code>\t</code></td> <td>horizontal tab</td> </tr> <tr> <td><code>\v</code></td> <td>vertical tab</td> </tr> <tr> <td><code>\cx</code></td> <td>a control-x character, for example, <code>$'\cZ'</code> to print the control sequence composed of Ctrl-Z (<code>^Z</code>)</td> </tr> <tr> <td><code>\uXXXX</code></td> <td>Interprets <code>XXXX</code> as a hexadecimal number and prints the corresponding character from the character set (4 digits) (Bash 4.2-alpha)</td> </tr> <tr> <td><code>\UXXXXXXXX</code></td> <td>Interprets <code>XXXX</code> as a hexadecimal number and prints the corresponding character from the character set (8 digits) (Bash 4.2-alpha)</td> </tr> <tr> <td><code>\nnn</code></td> <td>the eight-bit character whose value is the octal value nnn (one to three digits)</td> </tr> <tr> <td><code>\xHH</code></td> <td>the eight-bit character whose value is the hexadecimal value HH (one or two hex digits)</td> </tr> </tbody> </table> <p>This is especially useful when you want to pass special characters as arguments to some programs, like passing a newline to sed.</p> <p>The resulting text is treated as if it were <strong>single-quoted</strong>. No further expansion happens.</p> <p>The <code>$'...'</code> syntax comes from ksh93, but is portable to most modern shells including pdksh. A <a href="http://austingroupbugs.net/view.php?id=249#c590">specification</a> for it was accepted for SUS issue 7. There are still some stragglers, such as most ash variants including dash, (except busybox built with "bash compatibility" features).</p> <h2 id=i18nl10n>I18N/L10N<a class=headerlink href=#i18nl10n title="Permanent link">¶</a></h2> <p>A dollar-sign followed by a double-quoted string, for example</p> <div class=highlight><pre><span></span><code>echo $"generating database..."
|
|
</code></pre></div> <p>means I18N. If there is a translation available for that string, it is used instead of the given text. If not, or if the locale is <code>C</code>/<code>POSIX</code>, the dollar sign is simply ignored, which results in a normal double quoted string.</p> <p>If the string was replaced (translated), the result is double quoted.</p> <p>In case you're a C programmer: The purpose of <code>$"..."</code> is the same as for <code>gettext()</code> or <code>_()</code>.</p> <p>For useful examples to localize your scripts, please see <a href=http://tldp.org/LDP/abs/html/localization.html>Appendix I of the Advanced Bash Scripting Guide</a>.</p> <p><strong>Attention:</strong> There is a security hole. Please read <a href=http://www.gnu.org/software/gettext/manual/html_node/bash.html>the gettext documentation</a></p> <h2 id=common-mistakes>Common mistakes<a class=headerlink href=#common-mistakes title="Permanent link">¶</a></h2> <h3 id=string-lists-in-for-loops>String lists in for-loops<a class=headerlink href=#string-lists-in-for-loops title="Permanent link">¶</a></h3> <p>The <a href=../ccmd/classic_for/ >classic for loop</a> uses a list of words to iterate through. The list can also be in a variable:</p> <div class=highlight><pre><span></span><code>mylist="DOG CAT BIRD HORSE"
|
|
</code></pre></div> <p><strong><u>WRONG</u></strong> way to iterate through this list:</p> <div class=highlight><pre><span></span><code>for animal in "$mylist"; do
|
|
echo $animal
|
|
done
|
|
</code></pre></div> <p>Why? Due to the double-quotes, technically, the expansion of <code>$mylist</code> is seen as <strong>one word</strong>. The for loop iterates exactly one time, with <code>animal</code> set to the whole list.</p> <p><strong><u>RIGHT</u></strong> way to iterate through this list:</p> <div class=highlight><pre><span></span><code>for animal in $mylist; do
|
|
echo $animal
|
|
done
|
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</code></pre></div> <h3 id=working-out-the-test-command>Working out the test-command<a class=headerlink href=#working-out-the-test-command title="Permanent link">¶</a></h3> <p>The command <code>test</code> or <code>[ ... ]</code> (<a href=../../commands/classictest/ >the classic test command</a>) is an ordinary command, so ordinary syntax rules apply. Let's take string comparison as an example:</p> <div class=highlight><pre><span></span><code>[ WORD = WORD ]
|
|
</code></pre></div> <p>The <code>]</code> at the end is a convenience; if you type <code>which [</code> you will see that there is in fact a binary file with that name. So if we were writing this as a test command it would be:</p> <div class=highlight><pre><span></span><code>test WORD = WORD
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</code></pre></div> <p>When you compare variables, it's wise to quote them. Let's create a test string with spaces:</p> <div class=highlight><pre><span></span><code>mystring="my string"
|
|
</code></pre></div> <p>And now check that string against the word "testword":</p> <div class=highlight><pre><span></span><code>[ $mystring = testword ] # WRONG!
|
|
</code></pre></div> <p>This fails! These are too many arguments for the string comparison test. After expansion is performed, you really execute:</p> <div class=highlight><pre><span></span><code>[ my string = testword ]
|
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test my string = testword
|
|
</code></pre></div> <p>Which is wrong, because <code>my</code> and <code>string</code> are two separate arguments.</p> <p>So what you really want to do is:</p> <div class=highlight><pre><span></span><code>[ "$mystring" = testword ] # RIGHT!
|
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|
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test 'my string' = testword
|
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</code></pre></div> <p>Now the command has three parameters, which makes sense for a binary (two argument) operator.</p> <p><strong><u>Hint:</u></strong> Inside the <a href=../ccmd/conditional_expression/ >conditional expression</a> (<code>[[ ]]</code>) Bash doesn't perform word splitting, and thus you don't need to quote your variable references - they are always seen as "one word".</p> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li>Internal: <a href=../words/ >Some words about words...</a></li> <li>Internal: <a href=../expansion/wordsplit/ >Word splitting</a></li> <li>Internal: <a href=../expansion/intro/ >Introduction to expansions and substitutions</a></li> <li>External: <a href=http://www.grymoire.com/Unix/Quote.html>Grymore: Shellquoting</a></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">October 12, 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">October 12, 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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