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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> <a href=../scripting/bashbehaviour/ 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> 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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--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=#new-or-changed-commands-and-keywords class=md-nav__link> <span class=md-ellipsis> New or changed commands and keywords </span> </a> <nav class=md-nav aria-label="New or changed commands and keywords"> <ul class=md-nav__list> <li class=md-nav__item> <a href=#the-new-coproc-keyword class=md-nav__link> <span class=md-ellipsis> The new "coproc" keyword </span> </a> </li> <li class=md-nav__item> <a href=#the-new-mapfile-builtin class=md-nav__link> <span class=md-ellipsis> The new "mapfile" builtin </span> </a> </li> <li class=md-nav__item> <a href=#changes-to-the-case-keyword class=md-nav__link> <span class=md-ellipsis> Changes to the "case" keyword </span> </a> </li> <li class=md-nav__item> <a href=#changes-to-the-declare-builtin class=md-nav__link> <span class=md-ellipsis> Changes to the "declare" builtin </span> </a> </li> <li class=md-nav__item> <a href=#changes-to-the-read-builtin class=md-nav__link> <span class=md-ellipsis> Changes to the "read" builtin </span> </a> </li> <li class=md-nav__item> <a href=#changes-to-the-help-builtin class=md-nav__link> <span class=md-ellipsis> Changes to the "help" builtin </span> </a> </li> <li class=md-nav__item> <a href=#changes-to-the-ulimit-builtin class=md-nav__link> <span class=md-ellipsis> Changes to the "ulimit" builtin </span> </a> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=#expansions class=md-nav__link> <span class=md-ellipsis> Expansions </span> </a> <nav class=md-nav aria-label=Expansions> <ul class=md-nav__list> <li class=md-nav__item> <a href=#brace-expansion class=md-nav__link> <span class=md-ellipsis> Brace Expansion </span> </a> </li> <li class=md-nav__item> <a href=#parameter-expansion class=md-nav__link> <span class=md-ellipsis> Parameter Expansion </span> </a> </li> <li class=md-nav__item> <a href=#substring-expansion class=md-nav__link> <span class=md-ellipsis> Substring expansion </span> </a> </li> <li class=md-nav__item> <a href=#globbing class=md-nav__link> <span class=md-ellipsis> Globbing </span> </a> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=#associative-arrays class=md-nav__link> <span class=md-ellipsis> Associative Arrays </span> </a> </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=#interesting-new-shell-variables class=md-nav__link> <span class=md-ellipsis> Interesting new shell variables </span> </a> </li> <li class=md-nav__item> <a href=#interesting-new-shell-options class=md-nav__link> <span class=md-ellipsis> Interesting new Shell Options </span> </a> </li> <li class=md-nav__item> <a href=#misc class=md-nav__link> <span class=md-ellipsis> Misc </span> </a> </li> </ul> </nav> </div> </div> </div> <div class=md-content data-md-component=content> <article class="md-content__inner md-typeset"> <a href=https://github.com/flokoe/bash-hackers-wiki/edit/main/docs/bash4.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/bash4.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=bash-4-a-rough-overview>Bash 4 - a rough overview<a class=headerlink href=#bash-4-a-rough-overview title="Permanent link">¶</a></h1> <div class="admonition warning"> <p class=admonition-title>Attention</p> <p>Since Bash 4 has been around for quite some time now (4.3 will come soon), I consider it to be "standard". This page is not maintained anymore and is left here to keep your links working. See the <a href=../scripting/bashchanges/ >bashchanges</a> page for new stuff introduced.</p> </div> <p>Besides many bugfixes since Bash 3.2, Bash 4 will bring some interesting new features for shell users and scripters. See also <a href=../scripting/bashchanges/ >bashchanges</a> for a small general overview with more details.</p> <p>Not all of the changes and news are included here, just the biggest or most interesting ones. The changes to completion, and the readline component are not covered. <strong>Though, if you're familiar with these parts of Bash (and Bash 4), feel free to write a chapter here.</strong></p> <p>The complete list of fixes and changes is in the CHANGES or NEWS file of your Bash 4 distribution.</p> <p>The current available <strong>stable</strong> version is 4.4.18 release (February 03, 2018):</p> <ul> <li><a href=ftp://ftp.cwru.edu/pub/bash/bash-4.4.18.tar.gz>ftp://ftp.cwru.edu/pub/bash/bash-4.4.18.tar.gz</a></li> <li><a href=ftp://ftp.gnu.org/pub/gnu/bash/bash-4.4.18.tar.gz>ftp://ftp.gnu.org/pub/gnu/bash/bash-4.4.18.tar.gz</a></li> </ul> <h2 id=new-or-changed-commands-and-keywords>New or changed commands and keywords<a class=headerlink href=#new-or-changed-commands-and-keywords title="Permanent link">¶</a></h2> <h3 id=the-new-coproc-keyword>The new "coproc" keyword<a class=headerlink href=#the-new-coproc-keyword title="Permanent link">¶</a></h3> <p>Bash 4 introduces the concepts of coprocesses, a well known feature of other shells. The basic concept is simple: It will start any command in the background and set up an array that is populated with accessible files that represent the filedescriptors of the started process.</p> <p>In other words: It lets you start a process in background and communicate with its input and output data streams.</p> <p>See <a href=../syntax/keywords/coproc/ >The coproc keyword</a></p> <h3 id=the-new-mapfile-builtin>The new "mapfile" builtin<a class=headerlink href=#the-new-mapfile-builtin title="Permanent link">¶</a></h3> <p>The <code>mapfile</code> builtin is able to map the lines of a file directly into an array. This avoids having to fill an array yourself using a loop. It enables you to define the range of lines to read, and optionally call a callback, for example to display a progress bar.</p> <p>See: <a href=../commands/builtin/mapfile/ >mapfile</a></p> <h3 id=changes-to-the-case-keyword>Changes to the "case" keyword<a class=headerlink href=#changes-to-the-case-keyword title="Permanent link">¶</a></h3> <p>The <code>case</code> construct understands two new action list terminators:</p> <p>The <code>;&</code> terminator causes execution to continue with the next action list (rather than terminate the <code>case</code> construct).</p> <p>The <code>;;&</code> terminator causes the <code>case</code> construct to test the next given pattern instead of terminating the whole execution.</p> <p>See <a href=../syntax/ccmd/case/ >case</a></p> <h3 id=changes-to-the-declare-builtin>Changes to the "declare" builtin<a class=headerlink href=#changes-to-the-declare-builtin title="Permanent link">¶</a></h3> <p>The <code>-p</code> option now prints all attributes and values of declared variables (or functions, when used with <code>-f</code>). The output is fully re-usable as input.</p> <p>The new option <code>-l</code> declares a variable in a way that the content is converted to lowercase on assignment. For uppercase, the same applies to <code>-u</code>. The option <code>-c</code> causes the content to be capitalized before assignment.</p> <p><code>declare -A</code> declares associative arrays (see below).</p> <h3 id=changes-to-the-read-builtin>Changes to the "read" builtin<a class=headerlink href=#changes-to-the-read-builtin title="Permanent link">¶</a></h3> <p>The <code>read</code> builtin command has some interesting new features.</p> <p>The <code>-t</code> option to specify a timeout value has been slightly tuned. It now accepts fractional values and the special value 0 (zero). When <code>-t 0</code> is specified, <code>read</code> immediately returns with an exit status indicating if there's data waiting or not. However, when a timeout is given, and the <code>read</code> builtin times out, any partial data recieved up to the timeout is stored in the given variable, rather than lost. When a timeout is hit, <code>read</code> exits with a code greater than 128.</p> <p>A new option, <code>-i</code>, was introduced to be able to preload the input buffer with some text (when Readline is used, with <code>-e</code>). The user is able to change the text, or press return to accept it.</p> <p>See <a href=../commands/builtin/read/ >read</a></p> <h3 id=changes-to-the-help-builtin>Changes to the "help" builtin<a class=headerlink href=#changes-to-the-help-builtin title="Permanent link">¶</a></h3> <p>The builtin itself didn't change much, but the data displayed is more structured now. The help texts are in a better format, much easier to read.</p> <p>There are two new options: <code>-d</code> displays the summary of a help text, <code>-m</code> displays a manpage-like format.</p> <h3 id=changes-to-the-ulimit-builtin>Changes to the "ulimit" builtin<a class=headerlink href=#changes-to-the-ulimit-builtin title="Permanent link">¶</a></h3> <p>Besides the use of the 512 bytes blocksize everywhere in POSIX mode, <code>ulimit</code> supports two new limits: <code>-b</code> for max socket buffer size and <code>-T</code> for max number of threads.</p> <h2 id=expansions>Expansions<a class=headerlink href=#expansions title="Permanent link">¶</a></h2> <h3 id=brace-expansion>Brace Expansion<a class=headerlink href=#brace-expansion title="Permanent link">¶</a></h3> <p>The brace expansion was tuned to provide expansion results with leading zeros when requesting a row of numbers.</p> <p>See <a href=../syntax/expansion/brace/ >brace</a></p> <h3 id=parameter-expansion>Parameter Expansion<a class=headerlink href=#parameter-expansion title="Permanent link">¶</a></h3> <p>Methods to modify the case on expansion time have been added.</p> <p>On expansion time you can modify the syntax by adding operators to the parameter name.</p> <p>See <a href=../syntax/pe/#case_modification>Case modification on parameter expansion</a></p> <h3 id=substring-expansion>Substring expansion<a class=headerlink href=#substring-expansion title="Permanent link">¶</a></h3> <p>When using substring expansion on the positional parameters, a starting index of 0 now causes \$0 to be prepended to the list (if the positional parameters are used). Before, this expansion started with \$1:</p> <div class=highlight><pre><span></span><code><a id=__codelineno-0-1 name=__codelineno-0-1 href=#__codelineno-0-1></a><span class=c1># this should display $0 on Bash v4, $1 on Bash v3</span>
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<a id=__codelineno-0-2 name=__codelineno-0-2 href=#__codelineno-0-2></a><span class=nb>echo</span><span class=w> </span><span class=si>${</span><span class=p>@:</span><span class=nv>0</span><span class=p>:</span><span class=nv>1</span><span class=si>}</span>
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</code></pre></div> <h3 id=globbing>Globbing<a class=headerlink href=#globbing title="Permanent link">¶</a></h3> <p>There's a new shell option <code>globstar</code>. When enabled, Bash will perform recursive globbing on <code>**</code> – this means it matches all directories and files from the current position in the filesystem, rather than only the current level.</p> <p>The new shell option <code>dirspell</code> enables spelling corrections on directory names during globbing.</p> <p>See <a href=../syntax/expansion/globs/ >globs</a></p> <h2 id=associative-arrays>Associative Arrays<a class=headerlink href=#associative-arrays title="Permanent link">¶</a></h2> <p>Besides the classic method of integer indexed arrays, Bash 4 supports associative arrays.</p> <p>An associative array is an array indexed by an arbitrary string, something like</p> <div class=highlight><pre><span></span><code><a id=__codelineno-1-1 name=__codelineno-1-1 href=#__codelineno-1-1></a><span class=nb>declare</span><span class=w> </span>-A<span class=w> </span>ASSOC
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<a id=__codelineno-1-2 name=__codelineno-1-2 href=#__codelineno-1-2></a>
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<a id=__codelineno-1-3 name=__codelineno-1-3 href=#__codelineno-1-3></a>ASSOC<span class=o>[</span>First<span class=o>]=</span><span class=s2>"first element"</span>
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<a id=__codelineno-1-4 name=__codelineno-1-4 href=#__codelineno-1-4></a>ASSOC<span class=o>[</span>Hello<span class=o>]=</span><span class=s2>"second element"</span>
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<a id=__codelineno-1-5 name=__codelineno-1-5 href=#__codelineno-1-5></a>ASSOC<span class=o>[</span>Peter<span class=w> </span>Pan<span class=o>]=</span><span class=s2>"A weird guy"</span>
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</code></pre></div> <p>See <a href=../syntax/arrays/ >arrays</a></p> <h2 id=redirection>Redirection<a class=headerlink href=#redirection title="Permanent link">¶</a></h2> <p>There is a new <code>&>></code> redirection operator, which appends the standard output and standard error to the named file. This is the same as the good old <code>>>FILE 2>&1</code> notation.</p> <p>The parser now understands <code>|&</code> as a synonym for <code>2>&1 |</code>, which redirects the standard error for a command through a pipe.</p> <p>See <a href=../syntax/redirection/ >redirection</a></p> <h2 id=interesting-new-shell-variables>Interesting new shell variables<a class=headerlink href=#interesting-new-shell-variables title="Permanent link">¶</a></h2> <table> <thead> <tr> <th>Variable</th> <th>Description</th> </tr> </thead> <tbody> <tr> <td><a href=../syntax/shellvars/#BASHPID>BASHPID</a></td> <td>contains the PID of the current shell (this is different than what <code>$$</code> does!)</td> </tr> <tr> <td><a href=../syntax/shellvars/#PROMPT_DIRTRIM>PROMPT_DIRTRIM</a></td> <td>specifies the max. level of unshortened pathname elements in the prompt</td> </tr> <tr> <td><a href=../syntax/shellvars/#FUNCNEST>FUNCNEST</a></td> <td>control the maximum number of shell function recursions</td> </tr> </tbody> </table> <p>See <a href=../syntax/shellvars/ >shellvars</a></p> <h2 id=interesting-new-shell-options>Interesting new Shell Options<a class=headerlink href=#interesting-new-shell-options title="Permanent link">¶</a></h2> <p>The mentioned shell options are <strong>off by default</strong> unless otherwise mentioned.</p> <table> <thead> <tr> <th>Option</th> <th>Description</th> </tr> </thead> <tbody> <tr> <td><code>checkjobs</code></td> <td>check for and report any running jobs at shell exit</td> </tr> <tr> <td><code>compat*</code></td> <td>set compatiblity modes for older shell versions (influences regular expression matching in <code>[[ ... ]]</code></td> </tr> <tr> <td><code>dirspell</code></td> <td>enables spelling corrections on directory names during globbing</td> </tr> <tr> <td><code>globstar</code></td> <td>enables recursive globbing with <code>**</code></td> </tr> <tr> <td><code>lastpipe</code></td> <td>(4.2) to execute the last command in a pipeline in the current environment</td> </tr> </tbody> </table> <p>See <a href=../internals/shell_options/ >shell_options</a></p> <h2 id=misc>Misc<a class=headerlink href=#misc title="Permanent link">¶</a></h2> <ul> <li>If a command is not found, the shell attempts to execute a shell function named <code>command_not_found_handle</code>, supplying the command words as the function arguments. This can be used to display userfriendly messages or perform different command searches</li> <li>The behaviour of the <code>set -e</code> (<code>errexit</code>) mode was changed, it now acts more intuitive (and is better documented in the manpage).</li> <li>The output target for the <code>xtrace</code> (<code>set -x</code>/<code>set +x</code>) feature is configurable <strong>since Bash 4.1</strong> (previously, it was fixed to <code>stderr</code>): a variable named <a href=../syntax/shellvars/#BASH_XTRACEFD>BASH_XTRACEFD</a> can be set to the filedescriptor that should get the output</li> <li>Bash 4.1 is able to log the history to syslog (only to be enabled at compile time in <code>config-top.h</code>)</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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