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HTML
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Dict </a> </li> <li class=md-tabs__item> <a href=../../howto/calculate-dc/ class=md-tabs__link> Howto </a> </li> <li class=md-tabs__item> <a href=../../internals/shell_options/ class=md-tabs__link> Internals </a> </li> <li class=md-tabs__item> <a href=../../misc/bashphorisms/ class=md-tabs__link> Misc </a> </li> <li class="md-tabs__item md-tabs__item--active"> <a href=../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 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3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M244.8 8C106.1 8 0 113.3 0 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C428.2 457.8 496 362.9 496 252 496 113.3 383.5 8 244.8 8M97.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </div> <div class=md-source__repository> flokoe/bash-hackers-wiki </div> </a> </div> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../.. class=md-nav__link> <span class=md-ellipsis> Start </span> </a> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_2> <label class=md-nav__link for=__nav_2 id=__nav_2_label tabindex=0> <span class=md-ellipsis> Commands </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=1 aria-labelledby=__nav_2_label aria-expanded=false> <label class=md-nav__title for=__nav_2> <span class="md-nav__icon md-icon"></span> Commands </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../commands/classictest/ class=md-nav__link> <span class=md-ellipsis> The classic test command </span> </a> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_2_2> <label class=md-nav__link for=__nav_2_2 id=__nav_2_2_label tabindex=0> <span class=md-ellipsis> Builtin </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=2 aria-labelledby=__nav_2_2_label aria-expanded=false> <label class=md-nav__title for=__nav_2_2> <span class="md-nav__icon md-icon"></span> Builtin </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../commands/builtin/caller/ class=md-nav__link> <span class=md-ellipsis> The caller builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/cd/ class=md-nav__link> <span class=md-ellipsis> The cd builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/declare/ class=md-nav__link> <span class=md-ellipsis> The declare builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/echo/ class=md-nav__link> <span class=md-ellipsis> The echo builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/eval/ class=md-nav__link> <span class=md-ellipsis> The eval builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/exec/ class=md-nav__link> <span class=md-ellipsis> The exec builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/exit/ class=md-nav__link> <span class=md-ellipsis> The exit builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/export/ class=md-nav__link> <span class=md-ellipsis> The export builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/kill/ class=md-nav__link> <span class=md-ellipsis> The kill builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/let/ class=md-nav__link> <span class=md-ellipsis> The let builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/local/ class=md-nav__link> <span class=md-ellipsis> The local builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/mapfile/ class=md-nav__link> <span class=md-ellipsis> The mapfile builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/printf/ class=md-nav__link> <span class=md-ellipsis> The printf command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/read/ class=md-nav__link> <span class=md-ellipsis> The read builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/readonly/ class=md-nav__link> <span class=md-ellipsis> The readonly builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/return/ class=md-nav__link> <span class=md-ellipsis> The return builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/set/ class=md-nav__link> <span class=md-ellipsis> The set builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/shift/ class=md-nav__link> <span class=md-ellipsis> The shift builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/shopt/ class=md-nav__link> <span class=md-ellipsis> The shopt builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/trap/ class=md-nav__link> <span class=md-ellipsis> The trap builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/unset/ class=md-nav__link> <span class=md-ellipsis> The unset builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../commands/builtin/wait/ class=md-nav__link> <span class=md-ellipsis> The wait builtin command </span> </a> </li> </ul> </nav> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_3> <label class=md-nav__link for=__nav_3 id=__nav_3_label tabindex=0> <span class=md-ellipsis> Dict </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=1 aria-labelledby=__nav_3_label aria-expanded=false> <label class=md-nav__title for=__nav_3> <span class="md-nav__icon md-icon"></span> Dict </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../dict/directory/ class=md-nav__link> <span class=md-ellipsis> Directory </span> </a> </li> <li class=md-nav__item> <a href=../../dict/end_of_options/ class=md-nav__link> <span class=md-ellipsis> End of Options </span> </a> </li> <li class=md-nav__item> <a href=../../dict/exit_status/ class=md-nav__link> <span class=md-ellipsis> Exit Status </span> </a> </li> <li class=md-nav__item> <a href=../../dict/file/ class=md-nav__link> <span class=md-ellipsis> File </span> </a> </li> <li class=md-nav__item> <a href=../../dict/filetimes/ class=md-nav__link> <span class=md-ellipsis> File timestamp </span> </a> </li> <li class=md-nav__item> <a href=../../dict/globbing/ class=md-nav__link> <span class=md-ellipsis> Globbing </span> </a> </li> <li class=md-nav__item> <a href=../../dict/hardlink/ class=md-nav__link> <span class=md-ellipsis> Hardlink </span> </a> </li> <li class=md-nav__item> <a href=../../dict/interpreter_directive/ class=md-nav__link> <span class=md-ellipsis> Interpreter Directive </span> </a> </li> <li class=md-nav__item> <a href=../../dict/parameter/ class=md-nav__link> <span class=md-ellipsis> Parameter </span> </a> </li> <li class=md-nav__item> <a href=../../dict/posix/ class=md-nav__link> <span class=md-ellipsis> POSIX </span> </a> </li> <li class=md-nav__item> <a href=../../dict/shell/ class=md-nav__link> <span class=md-ellipsis> Shell </span> </a> </li> <li class=md-nav__item> <a href=../../dict/special_file/ class=md-nav__link> <span class=md-ellipsis> Special file </span> </a> </li> <li class=md-nav__item> <a href=../../dict/symlink/ class=md-nav__link> <span class=md-ellipsis> Symlink </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_4> <label class=md-nav__link for=__nav_4 id=__nav_4_label tabindex=0> <span class=md-ellipsis> Howto </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=1 aria-labelledby=__nav_4_label aria-expanded=false> <label class=md-nav__title for=__nav_4> <span class="md-nav__icon md-icon"></span> Howto </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../howto/calculate-dc/ class=md-nav__link> <span class=md-ellipsis> Calculating with dc </span> </a> </li> <li class=md-nav__item> <a href=../../howto/collapsing_functions/ class=md-nav__link> <span class=md-ellipsis> Collapsing Functions </span> </a> </li> <li class=md-nav__item> <a href=../../howto/conffile/ class=md-nav__link> <span class=md-ellipsis> Config files for your script </span> </a> </li> <li class=md-nav__item> <a href=../../howto/dissectabadoneliner/ class=md-nav__link> <span class=md-ellipsis> Dissect a bad oneliner </span> </a> </li> <li class=md-nav__item> <a href=../../howto/edit-ed/ class=md-nav__link> <span class=md-ellipsis> Editing files via scripts with ed </span> </a> </li> <li class=md-nav__item> <a href=../../howto/getopts_tutorial/ class=md-nav__link> <span class=md-ellipsis> Small getopts tutorial </span> </a> </li> <li class=md-nav__item> <a href=../../howto/mutex/ class=md-nav__link> <span class=md-ellipsis> Lock your script (against parallel execution) </span> </a> </li> <li class=md-nav__item> <a href=../../howto/pax/ class=md-nav__link> <span class=md-ellipsis> pax - the POSIX archiver </span> </a> </li> <li class=md-nav__item> <a href=../../howto/redirection_tutorial/ class=md-nav__link> <span class=md-ellipsis> Illustrated Redirection Tutorial </span> </a> </li> <li class=md-nav__item> <a href=../../howto/testing-your-scripts/ class=md-nav__link> <span class=md-ellipsis> Testing your scripts </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_5> <label class=md-nav__link for=__nav_5 id=__nav_5_label tabindex=0> <span class=md-ellipsis> Internals </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=1 aria-labelledby=__nav_5_label aria-expanded=false> <label class=md-nav__title for=__nav_5> <span class="md-nav__icon md-icon"></span> Internals </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../internals/shell_options/ class=md-nav__link> <span class=md-ellipsis> List of shell options </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_6> <label class=md-nav__link for=__nav_6 id=__nav_6_label tabindex=0> <span class=md-ellipsis> Misc </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=1 aria-labelledby=__nav_6_label aria-expanded=false> <label class=md-nav__title for=__nav_6> <span class="md-nav__icon md-icon"></span> Misc </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../misc/bashphorisms/ class=md-nav__link> <span class=md-ellipsis> The Bashphorisms </span> </a> </li> <li class=md-nav__item> <a href=../../misc/readthesourceluke/ class=md-nav__link> <span class=md-ellipsis> Readthesourceluke </span> </a> </li> <li class=md-nav__item> <a href=../../misc/shell_humor/ class=md-nav__link> <span class=md-ellipsis> Shell Humor </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--active md-nav__item--section md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_7 checked> <label class=md-nav__link for=__nav_7 id=__nav_7_label tabindex> <span class=md-ellipsis> Scripting </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=1 aria-labelledby=__nav_7_label aria-expanded=true> <label class=md-nav__title for=__nav_7> <span class="md-nav__icon md-icon"></span> Scripting </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../bashbehaviour/ class=md-nav__link> <span class=md-ellipsis> Bash's behaviour </span> </a> </li> <li class=md-nav__item> <a href=../bashchanges/ class=md-nav__link> <span class=md-ellipsis> Bash changes </span> </a> </li> <li class=md-nav__item> <a href=../basics/ class=md-nav__link> <span class=md-ellipsis> The basics of shell scripting </span> </a> </li> <li class=md-nav__item> <a href=../debuggingtips/ class=md-nav__link> <span class=md-ellipsis> Debugging a script </span> </a> </li> <li class=md-nav__item> <a href=../newbie_traps/ class=md-nav__link> <span class=md-ellipsis> Beginner Mistakes </span> </a> </li> <li class=md-nav__item> <a href=../nonportable/ class=md-nav__link> <span class=md-ellipsis> Portability talk </span> </a> </li> <li class=md-nav__item> <a href=../obsolete/ class=md-nav__link> <span class=md-ellipsis> Obsolete and deprecated syntax </span> </a> </li> <li class=md-nav__item> <a href=../posparams/ class=md-nav__link> <span class=md-ellipsis> Handling positional parameters </span> </a> </li> <li class=md-nav__item> <a href=../processtree/ class=md-nav__link> <span class=md-ellipsis> Bash and the process tree </span> </a> </li> <li class="md-nav__item 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> Scripting with style </span> <span class="md-nav__icon md-icon"></span> </label> <a href=./ class="md-nav__link md-nav__link--active"> <span class=md-ellipsis> Scripting with style </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=#indentation-guidelines class=md-nav__link> <span class=md-ellipsis> Indentation guidelines </span> </a> <nav class=md-nav aria-label="Indentation guidelines"> <ul class=md-nav__list> <li class=md-nav__item> <a href=#breaking-up-lines class=md-nav__link> <span class=md-ellipsis> Breaking up lines </span> </a> </li> <li class=md-nav__item> <a href=#breaking-compound-commands class=md-nav__link> <span class=md-ellipsis> Breaking compound commands </span> </a> <nav class=md-nav aria-label="Breaking compound commands"> <ul class=md-nav__list> <li class=md-nav__item> <a href=#symbolic class=md-nav__link> <span class=md-ellipsis> Symbolic </span> </a> </li> <li class=md-nav__item> <a href=#ifthenelifelse class=md-nav__link> <span class=md-ellipsis> if/then/elif/else </span> </a> </li> <li class=md-nav__item> <a href=#for class=md-nav__link> <span class=md-ellipsis> for </span> </a> </li> <li class=md-nav__item> <a href=#whileuntil class=md-nav__link> <span class=md-ellipsis> while/until </span> </a> </li> <li class=md-nav__item> <a href=#the-case-construct class=md-nav__link> <span class=md-ellipsis> The case construct </span> </a> </li> </ul> </nav> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=#syntax-and-coding-guidelines class=md-nav__link> <span class=md-ellipsis> Syntax and coding guidelines </span> </a> <nav class=md-nav aria-label="Syntax and coding guidelines"> <ul class=md-nav__list> <li class=md-nav__item> <a href=#cryptic-constructs class=md-nav__link> <span class=md-ellipsis> Cryptic constructs </span> </a> </li> <li class=md-nav__item> <a href=#variable-names class=md-nav__link> <span class=md-ellipsis> Variable names </span> </a> </li> </ul> </nav> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=../terminalcodes/ class=md-nav__link> <span class=md-ellipsis> Terminal codes (ANSI/VT100) introduction </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_8> <label class=md-nav__link for=__nav_8 id=__nav_8_label tabindex=0> <span class=md-ellipsis> Snipplets </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=1 aria-labelledby=__nav_8_label aria-expanded=false> <label class=md-nav__title for=__nav_8> <span class="md-nav__icon md-icon"></span> Snipplets </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../snipplets/ class=md-nav__link> <span class=md-ellipsis> Small code snipplets </span> </a> </li> <li class=md-nav__item> <a href=../../snipplets/add_color_to_your_scripts/ class=md-nav__link> <span class=md-ellipsis> Add Color to your scripts </span> </a> </li> <li class=md-nav__item> <a href=../../snipplets/awkcsv/ class=md-nav__link> <span class=md-ellipsis> Using awk to deal with CSV that uses quoted/unquoted delimiters </span> </a> </li> <li class=md-nav__item> <a href=../../snipplets/filesize/ class=md-nav__link> <span class=md-ellipsis> Show size of a file </span> </a> </li> <li class=md-nav__item> <a href=../../snipplets/kill_bg_job_without_message/ class=md-nav__link> <span class=md-ellipsis> Kill a background job without a message </span> </a> </li> <li class=md-nav__item> <a href=../../snipplets/largestfile/ class=md-nav__link> <span class=md-ellipsis> Get largest file </span> </a> </li> <li class=md-nav__item> <a href=../../snipplets/pause_command/ class=md-nav__link> <span class=md-ellipsis> Pausing a script (like MSDOS pause command) </span> </a> </li> <li class=md-nav__item> <a href=../../snipplets/prargs/ class=md-nav__link> <span class=md-ellipsis> Print argument list for testing </span> </a> </li> <li class=md-nav__item> <a href=../../snipplets/print_horizontal_line/ class=md-nav__link> <span class=md-ellipsis> Print a horizontal line </span> </a> </li> <li class=md-nav__item> <a href=../../snipplets/rndstr/ class=md-nav__link> <span class=md-ellipsis> Print a random string or select random elements </span> </a> </li> <li class=md-nav__item> <a href=../../snipplets/screen_saverestore/ class=md-nav__link> <span class=md-ellipsis> Save and restore terminal/screen content </span> </a> </li> <li class=md-nav__item> <a href=../../snipplets/ssh_fetchkeys/ class=md-nav__link> <span class=md-ellipsis> Fetching SSH hostkeys without interaction </span> </a> </li> <li class=md-nav__item> <a href=../../snipplets/ssh_local_var/ class=md-nav__link> <span class=md-ellipsis> Run some bash commands with SSH remotely using local variables </span> </a> </li> <li class=md-nav__item> <a href=../../snipplets/wrapperargs/ class=md-nav__link> <span class=md-ellipsis> Generate code with own arguments properly quoted </span> </a> </li> <li class=md-nav__item> <a href=../../snipplets/xclip/ class=md-nav__link> <span class=md-ellipsis> X-Clipboard on Commandline </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_9> <label class=md-nav__link for=__nav_9 id=__nav_9_label tabindex=0> <span class=md-ellipsis> Syntax </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=1 aria-labelledby=__nav_9_label aria-expanded=false> <label class=md-nav__title for=__nav_9> <span class="md-nav__icon md-icon"></span> Syntax </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../syntax/arith_expr/ class=md-nav__link> <span class=md-ellipsis> Arithmetic expressions </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/arrays/ class=md-nav__link> <span class=md-ellipsis> Arrays </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/basicgrammar/ class=md-nav__link> <span class=md-ellipsis> Basic grammar rules of Bash </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/pattern/ class=md-nav__link> <span class=md-ellipsis> Patterns and pattern matching </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/pe/ class=md-nav__link> <span class=md-ellipsis> Parameter expansion </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/quoting/ class=md-nav__link> <span class=md-ellipsis> Quotes and escaping </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/redirection/ class=md-nav__link> <span class=md-ellipsis> Redirection </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/shellvars/ class=md-nav__link> <span class=md-ellipsis> Special parameters and shell variables </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/words/ class=md-nav__link> <span class=md-ellipsis> Words... </span> </a> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_9_10> <label class=md-nav__link for=__nav_9_10 id=__nav_9_10_label tabindex=0> <span class=md-ellipsis> Ccmd </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=2 aria-labelledby=__nav_9_10_label aria-expanded=false> <label class=md-nav__title for=__nav_9_10> <span class="md-nav__icon md-icon"></span> Ccmd </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../syntax/ccmd/arithmetic_eval/ class=md-nav__link> <span class=md-ellipsis> Arithmetic evaluation (command) </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/ccmd/c_for/ class=md-nav__link> <span class=md-ellipsis> The C-style for-loop </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/ccmd/case/ class=md-nav__link> <span class=md-ellipsis> The case statement </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/ccmd/classic_for/ class=md-nav__link> <span class=md-ellipsis> The classic for-loop </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/ccmd/conditional_expression/ class=md-nav__link> <span class=md-ellipsis> The conditional expression </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/ccmd/grouping_plain/ class=md-nav__link> <span class=md-ellipsis> Grouping commands </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/ccmd/grouping_subshell/ class=md-nav__link> <span class=md-ellipsis> Grouping commands in a subshell </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/ccmd/if_clause/ class=md-nav__link> <span class=md-ellipsis> The if-clause </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/ccmd/intro/ class=md-nav__link> <span class=md-ellipsis> Bash compound commands </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/ccmd/until_loop/ class=md-nav__link> <span class=md-ellipsis> The until loop </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/ccmd/user_select/ class=md-nav__link> <span class=md-ellipsis> User selections </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/ccmd/while_loop/ class=md-nav__link> <span class=md-ellipsis> The while-loop </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_9_11> <label class=md-nav__link for=__nav_9_11 id=__nav_9_11_label tabindex=0> <span class=md-ellipsis> Expansion </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=2 aria-labelledby=__nav_9_11_label aria-expanded=false> <label class=md-nav__title for=__nav_9_11> <span class="md-nav__icon md-icon"></span> Expansion </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../syntax/expansion/arith/ class=md-nav__link> <span class=md-ellipsis> Arithmetic expansion </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/expansion/brace/ class=md-nav__link> <span class=md-ellipsis> Brace expansion </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/expansion/cmdsubst/ class=md-nav__link> <span class=md-ellipsis> Command substitution </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/expansion/globs/ class=md-nav__link> <span class=md-ellipsis> Pathname expansion (globbing) </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/expansion/intro/ class=md-nav__link> <span class=md-ellipsis> Expansions and substitutions </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/expansion/proc_subst/ class=md-nav__link> <span class=md-ellipsis> Process substitution </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/expansion/tilde/ class=md-nav__link> <span class=md-ellipsis> Tilde expansion </span> </a> </li> <li class=md-nav__item> <a href=../../syntax/expansion/wordsplit/ class=md-nav__link> <span class=md-ellipsis> Word splitting </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_9_12> <label class=md-nav__link for=__nav_9_12 id=__nav_9_12_label tabindex=0> <span class=md-ellipsis> Grammar </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=2 aria-labelledby=__nav_9_12_label aria-expanded=false> <label class=md-nav__title for=__nav_9_12> <span class="md-nav__icon md-icon"></span> Grammar </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../syntax/grammar/parser_exec/ class=md-nav__link> <span class=md-ellipsis> Parser exec </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_9_13> <label class=md-nav__link for=__nav_9_13 id=__nav_9_13_label tabindex=0> <span class=md-ellipsis> Keywords </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=2 aria-labelledby=__nav_9_13_label aria-expanded=false> <label class=md-nav__title for=__nav_9_13> <span class="md-nav__icon md-icon"></span> Keywords </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../syntax/keywords/coproc/ class=md-nav__link> <span class=md-ellipsis> The coproc keyword </span> </a> </li> </ul> </nav> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=../../tags/ class=md-nav__link> <span class=md-ellipsis> Tags </span> </a> </li> </ul> </nav> </div> </div> </div> <div class="md-sidebar md-sidebar--secondary" data-md-component=sidebar data-md-type=toc> <div class=md-sidebar__scrollwrap> <div class=md-sidebar__inner> <nav class="md-nav md-nav--secondary" aria-label="Table of contents"> <label class=md-nav__title for=__toc> <span class="md-nav__icon md-icon"></span> Table of contents </label> <ul class=md-nav__list data-md-component=toc data-md-scrollfix> <li class=md-nav__item> <a href=#indentation-guidelines class=md-nav__link> <span class=md-ellipsis> Indentation guidelines </span> </a> <nav class=md-nav aria-label="Indentation guidelines"> <ul class=md-nav__list> <li class=md-nav__item> <a href=#breaking-up-lines class=md-nav__link> <span class=md-ellipsis> Breaking up lines </span> </a> </li> <li class=md-nav__item> <a href=#breaking-compound-commands class=md-nav__link> <span class=md-ellipsis> Breaking compound commands </span> </a> <nav class=md-nav aria-label="Breaking compound commands"> <ul class=md-nav__list> <li class=md-nav__item> <a href=#symbolic class=md-nav__link> <span class=md-ellipsis> Symbolic </span> </a> </li> <li class=md-nav__item> <a href=#ifthenelifelse class=md-nav__link> <span class=md-ellipsis> if/then/elif/else </span> </a> </li> <li class=md-nav__item> <a href=#for class=md-nav__link> <span class=md-ellipsis> for </span> </a> </li> <li class=md-nav__item> <a href=#whileuntil class=md-nav__link> <span class=md-ellipsis> while/until </span> </a> </li> <li class=md-nav__item> <a href=#the-case-construct class=md-nav__link> <span class=md-ellipsis> The case construct </span> </a> </li> </ul> </nav> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=#syntax-and-coding-guidelines class=md-nav__link> <span class=md-ellipsis> Syntax and coding guidelines </span> </a> <nav class=md-nav aria-label="Syntax and coding guidelines"> <ul class=md-nav__list> <li class=md-nav__item> <a href=#cryptic-constructs class=md-nav__link> <span class=md-ellipsis> Cryptic constructs </span> </a> </li> <li class=md-nav__item> <a href=#variable-names class=md-nav__link> <span class=md-ellipsis> Variable names </span> </a> </li> </ul> </nav> </li> </ul> </nav> </div> </div> </div> <div class=md-content data-md-component=content> <article class="md-content__inner md-typeset"> <a href=https://github.com/flokoe/bash-hackers-wiki/edit/main/docs/scripting/style.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/scripting/style.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=scripting-with-style>Scripting with style<a class=headerlink href=#scripting-with-style title="Permanent link">¶</a></h1> <div class="admonition warning"> <p class=admonition-title>FIXME</p> <p>continue</p> </div> <p>These are some coding guidelines that helped me to read and understand my own code over the years. They also will help to produce code that will be a bit more robust than "if something breaks, I know how to fix it".</p> <p>This is not a bible, of course. But I have seen so much ugly and terrible code (not only in shell) during all the years, that I'm 100% convinced there needs to be <em>some</em> code layout and style. No matter which one you use, use it throughout your code (at least don't change it within the same shellscript file); don't change your code layout with your mood.</p> <p>Some good code layout helps you to read your own code after a while. And of course it helps others to read the code.</p> <h2 id=indentation-guidelines>Indentation guidelines<a class=headerlink href=#indentation-guidelines title="Permanent link">¶</a></h2> <p>Indentation is nothing that technically influences a script, it's only for us humans.</p> <p>I'm used to seeing/using indentation of <em>two space characters</em> (though many may prefer 4 spaces, see below in the discussion section):</p> <ul> <li>it's easy and fast to type</li> <li>it's not a hard-tab that's displayed differently in different environments</li> <li>it's wide enough to give a visual break and small enough to not waste too much space on the line</li> </ul> <p>Speaking of hard-tabs: Avoid them if possible. They only make trouble. I can imagine one case where they're useful: Indenting <a href=../../syntax/redirection/#here_documents>here-documents</a>.</p> <h3 id=breaking-up-lines>Breaking up lines<a class=headerlink href=#breaking-up-lines title="Permanent link">¶</a></h3> <p>Whenever you need to break lines of long code, you should follow one of these two rules:</p> <p><u><strong>Indention using command width:</strong></u></p> <div class=highlight><pre><span></span><code>activate some_very_long_option \
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some_other_option
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</code></pre></div> <p><u><strong>Indention using two spaces:</strong></u></p> <div class=highlight><pre><span></span><code>activate some_very_long_option \
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some_other_option
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</code></pre></div> <p>Personally, with some exceptions, I prefer the first form because it supports the visual impression of "these belong together".</p> <h3 id=breaking-compound-commands>Breaking compound commands<a class=headerlink href=#breaking-compound-commands title="Permanent link">¶</a></h3> <p><a href=../../syntax/ccmd/intro/ >Compound commands</a> form the structures that make a shell script different from a stupid enumeration of commands. Usually they contain a kind of "head" and a "body" that contains command lists. This type of compound command is relatively easy to indent.</p> <p>I'm used to (not all points apply to all compound commands, just pick the basic idea):</p> <ul> <li>put the introducing keyword and the initial command list or parameters on one line ("head")</li> <li>put the "body-introducing" keyword on the same line</li> <li>the command list of the "body" on separate lines, indented by two spaces</li> <li>put the closing keyword on a separated line, indented like the initial introducing keyword</li> </ul> <p>What?! Well, here again:</p> <h5 id=symbolic>Symbolic<a class=headerlink href=#symbolic title="Permanent link">¶</a></h5> <div class=highlight><pre><span></span><code>HEAD_KEYWORD parameters; BODY_BEGIN
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BODY_COMMANDS
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BODY_END
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</code></pre></div> <h5 id=ifthenelifelse>if/then/elif/else<a class=headerlink href=#ifthenelifelse title="Permanent link">¶</a></h5> <p>This construct is a bit special, because it has keywords (<code>elif</code>, <code>else</code>) "in the middle". The visually appealing way is to indent them like this:</p> <div class=highlight><pre><span></span><code>if ...; then
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...
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elif ...; then
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...
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else
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...
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fi
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</code></pre></div> <h5 id=for>for<a class=headerlink href=#for title="Permanent link">¶</a></h5> <div class=highlight><pre><span></span><code>for f in /etc/*; do
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...
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done
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</code></pre></div> <h5 id=whileuntil>while/until<a class=headerlink href=#whileuntil title="Permanent link">¶</a></h5> <div class=highlight><pre><span></span><code>while [[ $answer != [YyNn] ]]; do
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...
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done
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</code></pre></div> <h5 id=the-case-construct>The case construct<a class=headerlink href=#the-case-construct title="Permanent link">¶</a></h5> <p>The <code>case</code> construct might need a bit more discussion here, since its structure is a bit more complex.</p> <p>In general, every new "layer" gets a new indentation level:</p> <div class=highlight><pre><span></span><code>case $input in
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hello)
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echo "You said hello"
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;;
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bye)
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echo "You said bye"
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if foo; then
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bar
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fi
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;;
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*)
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echo "You said something weird..."
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;;
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esac
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</code></pre></div> <p>Some notes:</p> <ul> <li>if not 100% needed, the optional left parenthesis on the pattern is not used</li> <li>the patterns (<code>hello)</code>) and the corresponding action terminator (<code>;;</code>) are indented at the same level</li> <li>the action command lists are indented one more level (and continue to have their own indentation, if needed)</li> <li>though optional, the very last action terminator is given</li> </ul> <h2 id=syntax-and-coding-guidelines>Syntax and coding guidelines<a class=headerlink href=#syntax-and-coding-guidelines title="Permanent link">¶</a></h2> <h3 id=cryptic-constructs>Cryptic constructs<a class=headerlink href=#cryptic-constructs title="Permanent link">¶</a></h3> <p>Cryptic constructs, we all know them, we all love them. If they are not 100% needed, avoid them, since nobody except you may be able to decipher them.</p> <p>It's - just like in C - the middle ground between smart, efficient and readable.</p> <p>If you need to use a cryptic construct, include a comment that explains what your "monster" does.</p> <h3 id=variable-names>Variable names<a class=headerlink href=#variable-names title="Permanent link">¶</a></h3> <p>Since all reserved variables are <code>UPPERCASE</code>, the safest way is to only use <code>lowercase</code> variable names. This is true for reading user input, loop counting variables, etc., ... (in the example: <code>file</code>)</p> <ul> <li>prefer <code>lowercase</code> variables</li> <li>if you use <code>UPPERCASE</code> names, <strong>do not use reserved variable names</strong> (see <a href=http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap08.html#tag_08>SUS</a> for an incomplete list)</li> <li> <p>if you use <code>UPPERCASE</code> names, prepend the name with a unique prefix (<code>MY_</code> in the example below)</p> <h1 id=binbash>!/bin/bash<a class=headerlink href=#binbash title="Permanent link">¶</a></h1> <h1 id=the-prefix-my_>the prefix 'MY_'<a class=headerlink href=#the-prefix-my_ title="Permanent link">¶</a></h1> <p>MY_LOG_DIRECTORY=/var/adm/</p> <p>for file in "$MY_LOG_DIRECTORY"/*; do echo "Found Logfile: $file" done</p> </li> </ul> <h3 id=variable-initialization>Variable initialization<a class=headerlink href=#variable-initialization title="Permanent link">¶</a></h3> <p>As in C, it's always a good idea to initialize your variables, though, the shell will initialize fresh variables itself (better: Unset variables will generally behave like variables containing a null string).</p> <p>It's no problem to pass an <strong>environment variable</strong> to the script. If you blindly assume that all variables you use for the first time are <strong>empty</strong>, anybody can <strong>inject</strong> content into a variable by passing it via the environment.</p> <p>The solution is simple and effective: <strong>Initialize them</strong></p> <div class=highlight><pre><span></span><code>my_input=""
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my_array=()
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my_number=0
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</code></pre></div> <p>If you do that for every variable you use, then you also have some in-code documentation for them.</p> <h3 id=parameter-expansion>Parameter expansion<a class=headerlink href=#parameter-expansion title="Permanent link">¶</a></h3> <p>Unless you are really sure what you're doing, <strong>quote every parameter expansion</strong>.</p> <p>There are some cases where this isn't needed from a technical point of view, e.g.</p> <ul> <li>inside <code>[[ ... ]]</code> (other than the RHS of the <code>==</code>, <code>!=</code>, and <code>=~</code> operators)</li> <li>the parameter (<code>WORD</code>) in <code>case $WORD in ....</code></li> <li>variable assignment: <code>VAR=$WORD</code></li> </ul> <p>But quoting these is never a mistake. If you quote every parameter expansion, you'll be safe.</p> <p>If you need to parse a parameter as a list of words, you can't quote, of course, e.g.</p> <div class=highlight><pre><span></span><code>list="one two three"
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# you MUST NOT quote $list here
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for word in $list; do
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...
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done
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</code></pre></div> <h3 id=function-names>Function names<a class=headerlink href=#function-names title="Permanent link">¶</a></h3> <p>Function names should be all <code>lowercase</code> and meaningful. The function names should be human readable. A function named <code>f1</code> may be easy and quick to write down, but for debugging and especially for other people, it reveals nothing. Good names help document your code without using extra comments.</p> <p><strong>do not use command names for your functions</strong>. e.g. naming a script or function <code>test</code>, will collide with the UNIX <code>test</code> command.</p> <p>Unless absolutely necessary, only use alphanumeric characters and the underscore for function names. <code>/bin/ls</code> is a valid function name in Bash, but is not a good idea.</p> <h3 id=command-substitution>Command substitution<a class=headerlink href=#command-substitution title="Permanent link">¶</a></h3> <p>As noted in <a href=../../syntax/expansion/cmdsubst/ >the article about command substitution</a>, you should use the <code>$( ... )</code> form.</p> <p>If portability is a concern, use the backquoted form <code>` ... `</code>.</p> <p>In any case, if other expansions and word splitting are not wanted, you should quote the command substitution!</p> <h3 id=eval>Eval<a class=headerlink href=#eval title="Permanent link">¶</a></h3> <p>Well, like Greg says: <strong>"If eval is the answer, surely you are asking the wrong question."</strong></p> <p>Avoid it, unless absolutely neccesary:</p> <ul> <li><code>eval</code> can be your neckshot</li> <li>there are most likely other ways to achieve what you want</li> <li>if possible, re-think the way your script works, if it seems you can't avoid <code>eval</code> with your current method</li> <li>if you really, really, have to use it, then take care, and be sure about what you're doing</li> </ul> <h2 id=basic-structure>Basic structure<a class=headerlink href=#basic-structure title="Permanent link">¶</a></h2> <p>The basic structure of a script simply reads:</p> <div class=highlight><pre><span></span><code>#!SHEBANG
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CONFIGURATION_VARIABLES
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FUNCTION_DEFINITIONS
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MAIN_CODE
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</code></pre></div> <h3 id=the-shebang>The shebang<a class=headerlink href=#the-shebang title="Permanent link">¶</a></h3> <p>If possible (I know it's not always possible!), use a <a href=../../dict/interpreter_directive/ >shebang</a>.</p> <p>Be careful with <code>/bin/sh</code>: The argument that "on Linux <code>/bin/sh</code> is Bash" <strong>is a lie</strong> (and technically irrelevant)</p> <p>The shebang serves two purposes for me:</p> <ul> <li>it specifies the interpreter to be used when the script file is called directly: If you code for Bash, specify <code>bash</code>!</li> <li>it documents the desired interpreter (so: use <code>bash</code> when you write a Bash-script, use <code>sh</code> when you write a general Bourne/POSIX script, ...)</li> </ul> <h3 id=configuration-variables>Configuration variables<a class=headerlink href=#configuration-variables title="Permanent link">¶</a></h3> <p>I call variables that are meant to be changed by the user "configuration variables" here.</p> <p>Make them easy to find (directly at the top of the script), give them meaningful names and maybe a short comment. As noted above, use <code>UPPERCASE</code> for them only when you're sure about what you're doing. <code>lowercase</code> will be the safest.</p> <h3 id=function-definitions>Function definitions<a class=headerlink href=#function-definitions title="Permanent link">¶</a></h3> <p>Unless there are reasons not to, all function definitions should be declared before the main script code runs. This gives a far better overview and ensures that all function names are known before they are used.</p> <p>Since a function isn't parsed before it is executed, you usually don't have to ensure they're in a specific order.</p> <p>The portable form of the function definition should be used, without the <code>function</code> keyword (here using the <a href=../../syntax/ccmd/grouping_plain/ >grouping compound command</a>):</p> <div class=highlight><pre><span></span><code>getargs() {
|
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...
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}
|
|
</code></pre></div> <p>Speaking about the command grouping in function definitions using <code>{ ...; }</code>: If you don't have a good reason to use another compound command directly, you should always use this one.</p> <h2 id=behaviour-and-robustness>Behaviour and robustness<a class=headerlink href=#behaviour-and-robustness title="Permanent link">¶</a></h2> <h3 id=fail-early>Fail early<a class=headerlink href=#fail-early title="Permanent link">¶</a></h3> <p><strong>Fail early</strong>, this sounds bad, but usually is good. Failing early means to error out as early as possible when checks indicate an error or unmet condition. Failing early means to error out <strong>before</strong> your script begins its work in a potentially broken state.</p> <h3 id=availability-of-commands>Availability of commands<a class=headerlink href=#availability-of-commands title="Permanent link">¶</a></h3> <p>If you use external commands that may not be present on the path, or not installed, check for their availability, then tell the user they're missing.</p> <p>Example:</p> <div class=highlight><pre><span></span><code>my_needed_commands="sed awk lsof who"
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missing_counter=0
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for needed_command in $my_needed_commands; do
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if ! hash "$needed_command" >/dev/null 2>&1; then
|
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printf "Command not found in PATH: %s\n" "$needed_command" >&2
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((missing_counter++))
|
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fi
|
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done
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if ((missing_counter > 0)); then
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printf "Minimum %d commands are missing in PATH, aborting\n" "$missing_counter" >&2
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exit 1
|
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fi
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</code></pre></div> <h3 id=exit-meaningfully>Exit meaningfully<a class=headerlink href=#exit-meaningfully title="Permanent link">¶</a></h3> <p>The <a href=../../dict/exit_status/ >exit code</a> is your only way to directly communicate with the calling process without any special provisions.</p> <p>If your script exits, provide a meaningful exit code. That minimally means:</p> <ul> <li><code>exit 0</code> (zero) if everything is okay</li> <li><code>exit 1</code> - in general non-zero - if there was an error</li> </ul> <p>This, <strong>and only this</strong>, will enable the calling component to check the operation status of your script.</p> <p>You know: <strong>"One of the main causes of the fall of the Roman Empire was that, lacking zero, they had no way to indicate successful termination of their C programs."</strong> <em>-- Robert Firth</em></p> <h2 id=misc>Misc<a class=headerlink href=#misc title="Permanent link">¶</a></h2> <h3 id=output-and-appearance>Output and appearance<a class=headerlink href=#output-and-appearance title="Permanent link">¶</a></h3> <ul> <li>if the script is interactive, if it works for you and if you think this is a nice feature, you can try to <a href=../../snipplets/screen_saverestore/ >save the terminal content and restore it</a> after execution</li> <li>output clean and understandable screen messages</li> <li>if applicable, you can use colors or specific prefixes to tag error and warning messages<ul> <li>make it easy for the user to identify those messages</li> </ul> </li> <li>write normal output to <code>STDOUT</code>. write error, warning and diagnostic messages to <code>STDERR</code><ul> <li>enables message filtering</li> <li>keeps the script from mixing output data with diagnostic, or error messages</li> <li>if the script gives syntax help (<code>-?</code> or <code>-h</code> or <code>--help</code> arguments), it should go to <code>STDOUT</code></li> </ul> </li> <li>if applicable, write error/diagnostic messages to a logfile<ul> <li>avoids screen clutter</li> <li>messages are available for diagnostic use</li> </ul> </li> </ul> <h3 id=input>Input<a class=headerlink href=#input title="Permanent link">¶</a></h3> <ul> <li>never blindly assume anything. If you want the user to input a number, <strong>check for numeric input, leading zeros</strong>, etc. If you have specific format or content needs, <strong>always validate the input!</strong></li> </ul> <h3 id=tooling>Tooling<a class=headerlink href=#tooling title="Permanent link">¶</a></h3> <ul> <li>some of these guidelines, such as indentation, positioning of "body-introducing" keywords, and portable function declarations, can be enforced by <a href=https://github.com/mvdan/sh>shfmt</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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