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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--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> <a href=../../quoting/ class=md-nav__link> <span class=md-ellipsis> Quotes and escaping </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=../../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--active md-nav__item--section md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_9_10 checked> <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=true> <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=../arithmetic_eval/ class=md-nav__link> <span class=md-ellipsis> Arithmetic evaluation (command) </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> The C-style for-loop </span> <span class="md-nav__icon md-icon"></span> </label> <a href=./ class="md-nav__link md-nav__link--active"> <span class=md-ellipsis> The C-style for-loop </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=#synopsis class=md-nav__link> <span class=md-ellipsis> Synopsis </span> </a> </li> <li class=md-nav__item> <a href=#description class=md-nav__link> <span class=md-ellipsis> Description </span> </a> <nav class=md-nav aria-label=Description> <ul class=md-nav__list> <li class=md-nav__item> <a href=#alternate-syntax class=md-nav__link> <span class=md-ellipsis> Alternate syntax </span> </a> </li> <li class=md-nav__item> <a href=#return-status class=md-nav__link> <span class=md-ellipsis> Return status </span> </a> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=#alternatives-and-best-practice class=md-nav__link> <span class=md-ellipsis> Alternatives and best practice </span> </a> </li> <li class=md-nav__item> <a href=#examples class=md-nav__link> <span class=md-ellipsis> Examples </span> </a> <nav class=md-nav aria-label=Examples> <ul class=md-nav__list> <li class=md-nav__item> <a href=#simple-counter class=md-nav__link> <span class=md-ellipsis> Simple counter </span> </a> </li> <li class=md-nav__item> <a href=#stepping-counter class=md-nav__link> <span class=md-ellipsis> Stepping counter </span> </a> </li> <li class=md-nav__item> <a href=#bits-analyzer class=md-nav__link> <span class=md-ellipsis> Bits analyzer </span> </a> </li> <li class=md-nav__item> <a href=#up-down-up-down class=md-nav__link> <span class=md-ellipsis> Up, down, up, down... </span> </a> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=#portability-considerations class=md-nav__link> <span class=md-ellipsis> Portability considerations </span> </a> </li> <li class=md-nav__item> <a href=#bugs class=md-nav__link> <span class=md-ellipsis> Bugs </span> </a> </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=../case/ class=md-nav__link> <span class=md-ellipsis> The case statement </span> </a> </li> <li class=md-nav__item> <a href=../classic_for/ class=md-nav__link> <span class=md-ellipsis> The classic for-loop </span> </a> </li> <li class=md-nav__item> <a href=../conditional_expression/ class=md-nav__link> <span class=md-ellipsis> The conditional expression </span> </a> </li> <li class=md-nav__item> <a href=../grouping_plain/ class=md-nav__link> <span class=md-ellipsis> Grouping commands </span> </a> </li> <li class=md-nav__item> <a href=../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=../if_clause/ class=md-nav__link> <span class=md-ellipsis> The if-clause </span> </a> </li> <li class=md-nav__item> <a href=../intro/ class=md-nav__link> <span class=md-ellipsis> Bash compound commands </span> </a> </li> <li class=md-nav__item> <a href=../until_loop/ class=md-nav__link> <span class=md-ellipsis> The until loop </span> </a> </li> <li class=md-nav__item> <a href=../user_select/ class=md-nav__link> <span class=md-ellipsis> User selections </span> </a> </li> <li class=md-nav__item> <a href=../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=#synopsis class=md-nav__link> <span class=md-ellipsis> Synopsis </span> </a> </li> <li class=md-nav__item> <a href=#description class=md-nav__link> <span class=md-ellipsis> Description </span> </a> <nav class=md-nav aria-label=Description> <ul class=md-nav__list> <li class=md-nav__item> <a href=#alternate-syntax class=md-nav__link> <span class=md-ellipsis> Alternate syntax </span> </a> </li> <li class=md-nav__item> <a href=#return-status class=md-nav__link> <span class=md-ellipsis> Return status </span> </a> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=#alternatives-and-best-practice class=md-nav__link> <span class=md-ellipsis> Alternatives and best practice </span> </a> </li> <li class=md-nav__item> <a href=#examples class=md-nav__link> <span class=md-ellipsis> Examples </span> </a> <nav class=md-nav aria-label=Examples> <ul class=md-nav__list> <li class=md-nav__item> <a href=#simple-counter class=md-nav__link> <span class=md-ellipsis> Simple counter </span> </a> </li> <li class=md-nav__item> <a href=#stepping-counter class=md-nav__link> <span class=md-ellipsis> Stepping counter </span> </a> </li> <li class=md-nav__item> <a href=#bits-analyzer class=md-nav__link> <span class=md-ellipsis> Bits analyzer </span> </a> </li> <li class=md-nav__item> <a href=#up-down-up-down class=md-nav__link> <span class=md-ellipsis> Up, down, up, down... </span> </a> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=#portability-considerations class=md-nav__link> <span class=md-ellipsis> Portability considerations </span> </a> </li> <li class=md-nav__item> <a href=#bugs class=md-nav__link> <span class=md-ellipsis> Bugs </span> </a> </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"> <a href=https://github.com/flokoe/bash-hackers-wiki/edit/main/docs/syntax/ccmd/c_for.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/ccmd/c_for.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=the-c-style-for-loop>The C-style for-loop<a class=headerlink href=#the-c-style-for-loop title="Permanent link">¶</a></h1> <h2 id=synopsis>Synopsis<a class=headerlink href=#synopsis title="Permanent link">¶</a></h2> <div class=highlight><pre><span></span><code>for (( <EXPR1> ; <EXPR2> ; <EXPR3> )); do
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<LIST>
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done
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# as a special case: without semicolon after ((...))
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for (( <EXPR1> ; <EXPR2> ; <EXPR3> )) do
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<LIST>
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done
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# alternative, historical and undocumented syntax
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for (( <EXPR1> ; <EXPR2> ; <EXPR3> )) {
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<LIST>
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}
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</code></pre></div> <h2 id=description>Description<a class=headerlink href=#description title="Permanent link">¶</a></h2> <p>The C-style for-loop is a <a href=../../basicgrammar/#compound_commands>compound command</a> derived from the equivalent ksh88 feature, which is in turn derived from the C "for" keyword. Its purpose is to provide a convenient way to evaluate arithmetic expressions in a loop, plus initialize any required arithmetic variables. It is one of the main "loop with a counter" mechanisms available in the language.</p> <p>The <code>((;;))</code> syntax at the top of the loop is not an ordinary <a href=../arithmetic_eval/ >arithmetic compound command</a>, but is part of the C-style for-loop's own syntax. The three sections separated by semicolons are <a href=../../arith_expr/ >arithmetic expression</a> contexts. Each time one of the sections is to be evaluated, the section is first processed for: brace, parameter, command, arithmetic, and process substitution/expansion as usual for arithmetic contexts. When the loop is entered for the first time, <code><EXPR1></code> is evaluated, then <code><EXPR2></code> is evaluated and checked. If <code><EXPR2></code> is true, then the loop body is executed. After the first and all subsequent iterations, <code><EXPR1></code> is skipped, <code><EXPR3></code> is evaluated, then <code><EXPR2></code> is evaluated and checked again. This process continues until <code><EXPR2></code> is false.</p> <ul> <li><code><EXPR1></code> is to <strong>initialize variables</strong> before the first run.</li> <li><code><EXPR2></code> is to <strong>check</strong> for a termination condition. This is always the last section to evaluate prior to leaving the loop.</li> <li><code><EXPR3></code> is to <strong>change</strong> conditions after every iteration. For example, incrementing a counter.</li> </ul> <p>:!: If one of these arithmetic expressions in the for-loop is empty, it behaves as if it would be 1 (<strong>TRUE</strong> in arithmetic context).</p> <p>:!: Like all loops (Both types of <code>for</code>-loop, <code>while</code> and <code>until</code>), this loop can be:</p> <ul> <li>Terminated (broken) by the <code>break</code> builtin, optionally as <code>break N</code> to break out of <code>N</code> levels of nested loops.</li> <li>Forced immediately to the next iteration using the <code>continue</code> builtin, optionally as the <code>continue N</code> analog to <code>break N</code>.</li> </ul> <p>The equivalent construct using a <a href=../while_loop/ >while loop</a> and the <a href=../arithmetic_eval/ >arithmetic expression compound command</a> would be structured as:</p> <div class=highlight><pre><span></span><code>(( <EXPR1> ))
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while (( <EXPR2> )); do
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<LIST>
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(( <EXPR3> ))
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done
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</code></pre></div> <p>The equivalent <code>while</code> construct isn't exactly the same, because both, the <code>for</code> and the <code>while</code> loop behave differently in case you use the <code>continue</code> command.</p> <h3 id=alternate-syntax>Alternate syntax<a class=headerlink href=#alternate-syntax title="Permanent link">¶</a></h3> <p>Bash, Ksh93, Mksh, and Zsh also provide an alternate syntax for the <code>for</code> loop - enclosing the loop body in <code>{...}</code> instead of <code>do ... done</code>:</p> <div class=highlight><pre><span></span><code>for ((x=1; x<=3; x++))
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{
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echo $x
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}
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</code></pre></div> <p>This syntax is <strong>not documented</strong> and shouldn't be used. I found the parser definitions for it in 1.x code, and in modern 4.x code. My guess is that it's there for compatibility reasons. Unlike the other aforementioned shells, Bash does not support the analogous syntax for <a href=../case/#portability_considerations>case..esac</a>.</p> <h3 id=return-status>Return status<a class=headerlink href=#return-status title="Permanent link">¶</a></h3> <p>The return status is that of the last command executed from <code><LIST></code>, or <code>FALSE</code> if any of the arithmetic expressions failed.</p> <h2 id=alternatives-and-best-practice>Alternatives and best practice<a class=headerlink href=#alternatives-and-best-practice title="Permanent link">¶</a></h2> <div center round todo 60%>TODO: Show some alternate usages involving functions and local variables for initialization.</div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <h3 id=simple-counter>Simple counter<a class=headerlink href=#simple-counter title="Permanent link">¶</a></h3> <p>A simple counter, the loop iterates 101 times ("0" to "100" are 101 numbers -> 101 runs!), and everytime the variable <code>x</code> is set to the current value.</p> <ul> <li>It <strong>initializes</strong> <code>x = 0</code></li> <li>Before every iteration it <strong>checks</strong> if <code>x ≤ 100</code></li> <li> <p>After every iteration it <strong>changes</strong> <code>x++</code></p> <p>for ((x = 0 ; x <= 100 ; x++)); do echo "Counter: $x" done</p> </li> </ul> <h3 id=stepping-counter>Stepping counter<a class=headerlink href=#stepping-counter title="Permanent link">¶</a></h3> <p>This is the very same counter (compare it to the simple counter example above), but the <strong>change</strong> that is made is a <code>x += 10</code>. That means, it will count from 0 to 100, but with a <strong>step of 10</strong>.</p> <div class=highlight><pre><span></span><code>for ((x = 0 ; x <= 100 ; x += 10)); do
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echo "Counter: $x"
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done
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</code></pre></div> <h3 id=bits-analyzer>Bits analyzer<a class=headerlink href=#bits-analyzer title="Permanent link">¶</a></h3> <p>This example loops through the bit-values of a Byte, beginning from 128, ending at 1. If that bit is set in the <code>testbyte</code>, it prints "<code>1</code>", else "<code>0</code>" => it prints the binary representation of the <code>testbyte</code> value (8 bits).</p> <div class=highlight><pre><span></span><code>#!/usr/bin/env bash
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# Example written for http://wiki.bash-hackers.org/syntax/ccmd/c_for#bits_analyzer
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# Based on TheBonsai's original.
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function toBin {
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typeset m=$1 n=2 x='x[(n*=2)>m]'
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for ((x = x; n /= 2;)); do
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printf %d $(( m & n && 1))
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done
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}
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function main {
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[[ $1 == +([0-9]) ]] || return
|
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typeset result
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|
if (( $(ksh -c 'printf %..2d $1' _ "$1") == ( result = $(toBin "$1") ) )); then
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printf '%s is %s in base 2!\n' "$1" "$result"
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else
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echo 'Oops, something went wrong with our calculation.' >&2
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exit 1
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fi
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}
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main "${1:-123}"
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# vim: set fenc=utf-8 ff=unix ft=sh :
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<div hide>
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testbyte=123
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for (( n = 128 ; n >= 1 ; n /= 2 )); do
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if (( testbyte & n )); then
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printf %d 1
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else
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printf %s 0
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fi
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done
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echo
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</div>
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</code></pre></div> <p>Why that one begins at 128 (highest value, on the left) and not 1 (lowest value, on the right)? It's easier to print from left to right...</p> <p>We arrive at 128 for <code>n</code> through the recursive arithmetic expression stored in <code>x</code>, which calculates the next-greatest power of 2 after <code>m</code>. To show that it works, we use ksh93 to double-check the answer, because it has a built-in feature for <code>printf</code> to print a representation of any number in an arbitrary base (up to 64). Very few languages have that ability built-in, even things like Python.</p> <h3 id=up-down-up-down>Up, down, up, down...<a class=headerlink href=#up-down-up-down title="Permanent link">¶</a></h3> <p>This counts up and down from <code>0</code> to <code>${1:-5}</code>, <code>${2:-4}</code> times, demonstrating more complicated arithmetic expressions with multiple variables.</p> <div class=highlight><pre><span></span><code>for (( incr = 1, n=0, times = ${2:-4}, step = ${1:-5}; (n += incr) % step || (incr *= -1, --times);)); do
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printf '%*s\n' "$((n+1))" "$n"
|
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done
|
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</code></pre></div> <div class=highlight><pre><span></span><code><a id=__codelineno-0-1 name=__codelineno-0-1 href=#__codelineno-0-1></a>~<span class=w> </span><span class=se>\$</span><span class=w> </span>bash<span class=w> </span><<span class=o>(</span>xclip<span class=w> </span>-o<span class=o>)</span><span class=w> </span><span class=m>1</span>
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<a id=__codelineno-0-2 name=__codelineno-0-2 href=#__codelineno-0-2></a>
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<a id=__codelineno-0-3 name=__codelineno-0-3 href=#__codelineno-0-3></a><span class=w> </span><span class=m>2</span>
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<a id=__codelineno-0-4 name=__codelineno-0-4 href=#__codelineno-0-4></a><span class=w> </span><span class=m>3</span>
|
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<a id=__codelineno-0-5 name=__codelineno-0-5 href=#__codelineno-0-5></a><span class=w> </span><span class=m>4</span>
|
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<a id=__codelineno-0-6 name=__codelineno-0-6 href=#__codelineno-0-6></a><span class=w> </span><span class=m>5</span>
|
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<a id=__codelineno-0-7 name=__codelineno-0-7 href=#__codelineno-0-7></a><span class=w> </span><span class=m>4</span>
|
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<a id=__codelineno-0-8 name=__codelineno-0-8 href=#__codelineno-0-8></a><span class=w> </span><span class=m>3</span>
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<a id=__codelineno-0-9 name=__codelineno-0-9 href=#__codelineno-0-9></a><span class=w> </span><span class=m>2</span>
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<a id=__codelineno-0-10 name=__codelineno-0-10 href=#__codelineno-0-10></a>
|
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<a id=__codelineno-0-11 name=__codelineno-0-11 href=#__codelineno-0-11></a><span class=m>1</span><span class=w> </span><span class=m>0</span><span class=w> </span><span class=m>1</span>
|
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<a id=__codelineno-0-12 name=__codelineno-0-12 href=#__codelineno-0-12></a>
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<a id=__codelineno-0-13 name=__codelineno-0-13 href=#__codelineno-0-13></a><span class=w> </span><span class=m>2</span>
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<a id=__codelineno-0-14 name=__codelineno-0-14 href=#__codelineno-0-14></a><span class=w> </span><span class=m>3</span>
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<a id=__codelineno-0-15 name=__codelineno-0-15 href=#__codelineno-0-15></a><span class=w> </span><span class=m>4</span>
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<a id=__codelineno-0-16 name=__codelineno-0-16 href=#__codelineno-0-16></a><span class=w> </span><span class=m>5</span>
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<a id=__codelineno-0-17 name=__codelineno-0-17 href=#__codelineno-0-17></a><span class=w> </span><span class=m>4</span>
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<a id=__codelineno-0-18 name=__codelineno-0-18 href=#__codelineno-0-18></a><span class=w> </span><span class=m>3</span>
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<a id=__codelineno-0-19 name=__codelineno-0-19 href=#__codelineno-0-19></a><span class=w> </span><span class=m>2</span>
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<a id=__codelineno-0-20 name=__codelineno-0-20 href=#__codelineno-0-20></a>
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<a id=__codelineno-0-21 name=__codelineno-0-21 href=#__codelineno-0-21></a><span class=m>1</span>
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|
</code></pre></div> <h2 id=portability-considerations>Portability considerations<a class=headerlink href=#portability-considerations title="Permanent link">¶</a></h2> <ul> <li>C-style for loops aren't POSIX. They are available in Bash, ksh93, and zsh. All 3 have essentially the same syntax and behavior.</li> <li>C-style for loops aren't available in mksh.</li> </ul> <h2 id=bugs>Bugs<a class=headerlink href=#bugs title="Permanent link">¶</a></h2> <ul> <li><em>Fixed in 4.3</em>. ~~There appears to be a bug as of Bash 4.2p10 in which command lists can't be distinguished from the for loop's arithmetic argument delimiter (both semicolons), so command substitutions within the C-style for loop expression can't contain more than one command.~~</li> </ul> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li>Internal: <a href=../../arith_expr/ >Arithmetic expressions</a></li> <li>Internal: <a href=../classic_for/ >The classic for-loop</a></li> <li>Internal: <a href=../while_loop/ >The while-loop</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">November 7, 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 7, 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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