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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><link href=https://flokoe.github.io/bash-hackers-wiki/snipplets/rndstr/ rel=canonical><link href=../print_horizontal_line/ rel=prev><link href=../screen_saverestore/ rel=next><link rel=icon href=../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.5.44"><title>Print a random string or select random elements - The Bash Hackers Wiki</title><link rel=stylesheet href=../../assets/stylesheets/main.0253249f.min.css><link rel=stylesheet href=../../assets/stylesheets/palette.06af60db.min.css><link rel=preconnect href=https://fonts.gstatic.com crossorigin><link rel=stylesheet href="https://fonts.googleapis.com/css?family=Roboto:300,300i,400,400i,700,700i%7CRoboto+Mono:400,400i,700,700i&display=fallback"><style>:root{--md-text-font:"Roboto";--md-code-font:"Roboto Mono"}</style><script>__md_scope=new URL("../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#print-a-random-string-or-select-random-elements class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../.. title="The Bash Hackers Wiki" class="md-header__button md-logo" aria-label="The Bash Hackers Wiki" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> The Bash Hackers Wiki </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> Print a random string or select random elements </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo 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1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <div class=md-search data-md-component=search role=dialog> <label class=md-search__overlay for=__search></label> <div class=md-search__inner role=search> <form class=md-search__form name=search> <input type=text class=md-search__input name=query aria-label=Search placeholder=Search autocapitalize=off autocorrect=off autocomplete=off spellcheck=false data-md-component=search-query required> <label class="md-search__icon md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 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<a href=../../dict/directory/ class=md-tabs__link> Dict </a> </li> <li class=md-tabs__item> <a href=../../howto/calculate-dc/ class=md-tabs__link> Howto </a> </li> <li class=md-tabs__item> <a href=../../internals/shell_options/ class=md-tabs__link> Internals </a> </li> <li class=md-tabs__item> <a href=../../misc/bashphorisms/ class=md-tabs__link> Misc </a> </li> <li class=md-tabs__item> <a href=../../scripting/bashbehaviour/ class=md-tabs__link> Scripting </a> </li> <li class="md-tabs__item md-tabs__item--active"> <a href=../ 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 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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--active md-nav__item--section md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_8 checked> <label class=md-nav__link for=__nav_8 id=__nav_8_label tabindex> <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=true> <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=../ class=md-nav__link> <span class=md-ellipsis> Small code snipplets </span> </a> </li> <li class=md-nav__item> <a href=../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=../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=../filesize/ class=md-nav__link> <span class=md-ellipsis> Show size of a file </span> </a> </li> <li class=md-nav__item> <a href=../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=../largestfile/ class=md-nav__link> <span class=md-ellipsis> Get largest file </span> </a> </li> <li class=md-nav__item> <a href=../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=../prargs/ class=md-nav__link> <span class=md-ellipsis> Print argument list for testing </span> </a> </li> <li class=md-nav__item> <a href=../print_horizontal_line/ class=md-nav__link> <span class=md-ellipsis> Print a horizontal line </span> </a> </li> <li class="md-nav__item md-nav__item--active"> <input class="md-nav__toggle md-toggle" type=checkbox id=__toc> <a href=./ class="md-nav__link md-nav__link--active"> <span class=md-ellipsis> Print a random string or select random elements </span> </a> </li> <li class=md-nav__item> <a href=../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=../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=../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=../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=../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"> </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/snipplets/rndstr.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/snipplets/rndstr.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=print-a-random-string-or-select-random-elements>Print a random string or select random elements<a class=headerlink href=#print-a-random-string-or-select-random-elements title="Permanent link">&para;</a></h1> <p>---- dataentry snipplet ---- snipplet_tags: terminal, line LastUpdate_dt: 2013-04-30 Contributors: Dan Douglas (ormaaj) type: snipplet</p> <hr> <p>First off, here is a fast / reliable random string function for scripts or libraries which can optionally assign directly to a variable.</p> <div class=highlight><pre><span></span><code><a id=__codelineno-0-1 name=__codelineno-0-1 href=#__codelineno-0-1></a><span class=c1># Print or assign a random alphanumeric string of a given length.</span>
<a id=__codelineno-0-2 name=__codelineno-0-2 href=#__codelineno-0-2></a><span class=c1># rndstr len [ var ]</span>
<a id=__codelineno-0-3 name=__codelineno-0-3 href=#__codelineno-0-3></a><span class=k>function</span><span class=w> </span>rndstr<span class=w> </span><span class=o>{</span>
<a id=__codelineno-0-4 name=__codelineno-0-4 href=#__codelineno-0-4></a><span class=w> </span><span class=k>if</span><span class=w> </span><span class=o>[[</span><span class=w> </span><span class=nv>$FUNCNAME</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=s2>&quot;</span><span class=si>${</span><span class=nv>FUNCNAME</span><span class=p>[1]</span><span class=si>}</span><span class=s2>&quot;</span><span class=w> </span><span class=o>]]</span><span class=p>;</span><span class=w> </span><span class=k>then</span>
<a id=__codelineno-0-5 name=__codelineno-0-5 href=#__codelineno-0-5></a><span class=w> </span><span class=nb>unset</span><span class=w> </span>-v<span class=w> </span>a
<a id=__codelineno-0-6 name=__codelineno-0-6 href=#__codelineno-0-6></a><span class=w> </span><span class=nb>printf</span><span class=w> </span><span class=s2>&quot;</span><span class=nv>$@</span><span class=s2>&quot;</span>
<a id=__codelineno-0-7 name=__codelineno-0-7 href=#__codelineno-0-7></a><span class=w> </span><span class=k>elif</span><span class=w> </span><span class=o>[[</span><span class=w> </span><span class=nv>$1</span><span class=w> </span>!<span class=o>=</span><span class=w> </span>+<span class=o>([[</span>:digit:<span class=o>]])</span><span class=w> </span><span class=o>]]</span><span class=p>;</span><span class=w> </span><span class=k>then</span>
<a id=__codelineno-0-8 name=__codelineno-0-8 href=#__codelineno-0-8></a><span class=w> </span><span class=k>return</span><span class=w> </span><span class=m>1</span>
<a id=__codelineno-0-9 name=__codelineno-0-9 href=#__codelineno-0-9></a><span class=w> </span><span class=k>elif</span><span class=w> </span><span class=o>((</span><span class=w> </span><span class=nv>$1</span><span class=w> </span><span class=o>))</span><span class=p>;</span><span class=w> </span><span class=k>then</span>
<a id=__codelineno-0-10 name=__codelineno-0-10 href=#__codelineno-0-10></a><span class=w> </span><span class=nb>typeset</span><span class=w> </span>-a<span class=w> </span><span class=nv>a</span><span class=o>=({</span>a..z<span class=o>}</span><span class=w> </span><span class=o>{</span>A..Z<span class=o>}</span><span class=w> </span><span class=o>{</span><span class=m>0</span>..9<span class=o>})</span>
<a id=__codelineno-0-11 name=__codelineno-0-11 href=#__codelineno-0-11></a><span class=w> </span><span class=nb>eval</span><span class=w> </span><span class=s1>&#39;${2:+&quot;$FUNCNAME&quot; -v} &quot;${2:-printf}&quot; -- %s &quot;${a[RANDOM%&#39;</span><span class=s2>&quot;</span><span class=si>${#</span><span class=nv>a</span><span class=p>[@]</span><span class=si>}</span><span class=s2>&quot;</span><span class=s1>&#39;]&quot;{1..&#39;</span><span class=s2>&quot;</span><span class=nv>$1</span><span class=s2>&quot;</span><span class=s1>&#39;}&quot;}&quot;&#39;</span>
<a id=__codelineno-0-12 name=__codelineno-0-12 href=#__codelineno-0-12></a><span class=w> </span><span class=k>fi</span>
<a id=__codelineno-0-13 name=__codelineno-0-13 href=#__codelineno-0-13></a><span class=o>}</span>
</code></pre></div> <p>This example prints 10 random positional parameters and operates on basically the same principle as the <code>rndstr</code> function above.</p> <div class=highlight><pre><span></span><code> ~ $ ( set -- foo bar baz bork; printf &#39;%s &#39; &quot;${!_[_=RANDOM%$#+1,0]&quot;{0..10}&quot;}&quot;; echo )
bork bar baz baz foo baz baz baz baz baz bork
</code></pre></div> <div hide> This has some interesting option parsing concepts, but is overly complex. This is a good example of working too hard to avoid an eval for no benefit and some performance penalty. :/ <div class=highlight><pre><span></span><code><a id=__codelineno-1-1 name=__codelineno-1-1 href=#__codelineno-1-1></a><span class=c1># Print or assign a random alphanumeric string of a given length.</span>
<a id=__codelineno-1-2 name=__codelineno-1-2 href=#__codelineno-1-2></a><span class=c1># rndstr [ -v var ] len</span>
<a id=__codelineno-1-3 name=__codelineno-1-3 href=#__codelineno-1-3></a><span class=c1># Bash-only</span>
<a id=__codelineno-1-4 name=__codelineno-1-4 href=#__codelineno-1-4></a>rndstr<span class=o>()</span>
<a id=__codelineno-1-5 name=__codelineno-1-5 href=#__codelineno-1-5></a><span class=w> </span><span class=k>if</span><span class=w> </span><span class=o>[[</span><span class=w> </span><span class=nv>$FUNCNAME</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=s2>&quot;</span><span class=si>${</span><span class=nv>FUNCNAME</span><span class=p>[1]</span><span class=si>}</span><span class=s2>&quot;</span><span class=w> </span><span class=o>]]</span><span class=p>;</span><span class=w> </span><span class=k>then</span>
<a id=__codelineno-1-6 name=__codelineno-1-6 href=#__codelineno-1-6></a><span class=w> </span><span class=c1># On recursion, this branch unsets the outer scope&#39;s locals and assigns the result.</span>
<a id=__codelineno-1-7 name=__codelineno-1-7 href=#__codelineno-1-7></a><span class=w> </span><span class=nb>unset</span><span class=w> </span>-v<span class=w> </span>a<span class=w> </span>b
<a id=__codelineno-1-8 name=__codelineno-1-8 href=#__codelineno-1-8></a><span class=w> </span><span class=nb>printf</span><span class=w> </span>-v<span class=w> </span><span class=s2>&quot;</span><span class=nv>$1</span><span class=s2>&quot;</span><span class=w> </span>%s<span class=w> </span><span class=s2>&quot;</span><span class=si>${</span><span class=p>@:</span><span class=nv>2</span><span class=si>}</span><span class=s2>&quot;</span>
<a id=__codelineno-1-9 name=__codelineno-1-9 href=#__codelineno-1-9></a><span class=w> </span><span class=k>elif</span><span class=w> </span>!<span class=w> </span><span class=o>{</span><span class=w> </span><span class=o>[[</span><span class=w> </span><span class=nv>$1</span><span class=w> </span><span class=o>==</span><span class=w> </span>-v<span class=w> </span><span class=o>]]</span><span class=w> </span><span class=o>&amp;&amp;</span><span class=w> </span>shift<span class=p>;</span><span class=w> </span><span class=o>}</span><span class=p>;</span><span class=w> </span><span class=o>[[</span><span class=w> </span><span class=nv>$?</span>+1<span class=w> </span>-ne<span class=w> </span><span class=nv>$#</span><span class=w> </span><span class=o>||</span><span class=w> </span><span class=si>${</span><span class=p>!#</span><span class=si>}</span><span class=w> </span>!<span class=o>=</span><span class=w> </span>+<span class=o>([[</span>:digit:<span class=o>]])</span><span class=w> </span><span class=o>||</span><span class=w> </span><span class=o>(</span><span class=w> </span><span class=nv>$?</span><span class=w> </span>-gt<span class=w> </span><span class=m>0</span><span class=w> </span><span class=o>&amp;&amp;</span><span class=w> </span>-z<span class=w> </span><span class=nv>$1</span><span class=w> </span><span class=o>)</span><span class=w> </span><span class=o>]]</span><span class=p>;</span><span class=w> </span><span class=k>then</span>
<a id=__codelineno-1-10 name=__codelineno-1-10 href=#__codelineno-1-10></a><span class=w> </span><span class=c1># This branch does input validation, strips -v, and guarantees we&#39;re left with either 1 or 2 args.</span>
<a id=__codelineno-1-11 name=__codelineno-1-11 href=#__codelineno-1-11></a><span class=w> </span><span class=k>return</span><span class=w> </span><span class=m>1</span>
<a id=__codelineno-1-12 name=__codelineno-1-12 href=#__codelineno-1-12></a><span class=w> </span><span class=k>elif</span><span class=w> </span><span class=o>((</span><span class=w> </span>!<span class=w> </span><span class=si>${</span><span class=p>!#</span><span class=si>}</span><span class=w> </span><span class=o>))</span><span class=p>;</span><span class=w> </span><span class=k>then</span>
<a id=__codelineno-1-13 name=__codelineno-1-13 href=#__codelineno-1-13></a><span class=w> </span><span class=c1># If a zero-length string is requested, return success.</span>
<a id=__codelineno-1-14 name=__codelineno-1-14 href=#__codelineno-1-14></a><span class=w> </span><span class=k>return</span>
<a id=__codelineno-1-15 name=__codelineno-1-15 href=#__codelineno-1-15></a><span class=w> </span><span class=k>else</span>
<a id=__codelineno-1-16 name=__codelineno-1-16 href=#__codelineno-1-16></a><span class=w> </span><span class=c1># This line generates the string and assigns it to &quot;b&quot;.</span>
<a id=__codelineno-1-17 name=__codelineno-1-17 href=#__codelineno-1-17></a><span class=w> </span><span class=nb>local</span><span class=w> </span>-a<span class=w> </span><span class=nv>a</span><span class=o>=({</span>a..z<span class=o>}</span><span class=w> </span><span class=o>{</span>A..Z<span class=o>}</span><span class=w> </span><span class=o>{</span><span class=m>0</span>..9<span class=o>})</span><span class=w> </span><span class=s1>&#39;b=(&quot;${a[RANDOM%&#39;</span><span class=s2>&quot;</span><span class=si>${#</span><span class=nv>a</span><span class=p>[@]</span><span class=si>}</span><span class=s2>&quot;</span><span class=s1>&#39;]&quot;{1..&#39;</span><span class=s2>&quot;</span><span class=si>${</span><span class=p>!#</span><span class=si>}</span><span class=s2>&quot;</span><span class=s1>&#39;}&quot;}&quot;)&#39;</span>
<a id=__codelineno-1-18 name=__codelineno-1-18 href=#__codelineno-1-18></a><span class=w> </span><span class=k>if</span><span class=w> </span><span class=o>((</span><span class=w> </span><span class=nv>$#</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=m>2</span><span class=w> </span><span class=o>))</span><span class=p>;</span><span class=w> </span><span class=k>then</span>
<a id=__codelineno-1-19 name=__codelineno-1-19 href=#__codelineno-1-19></a><span class=w> </span><span class=c1># If -v, then pass a variable name and value to assign and recurse once.</span>
<a id=__codelineno-1-20 name=__codelineno-1-20 href=#__codelineno-1-20></a><span class=w> </span><span class=s2>&quot;</span><span class=nv>$FUNCNAME</span><span class=s2>&quot;</span><span class=w> </span><span class=s2>&quot;</span><span class=nv>$1</span><span class=s2>&quot;</span><span class=w> </span><span class=s2>&quot;</span><span class=si>${</span><span class=nv>b</span><span class=p>[@]</span><span class=si>}</span><span class=s2>&quot;</span>
<a id=__codelineno-1-21 name=__codelineno-1-21 href=#__codelineno-1-21></a><span class=w> </span><span class=k>else</span>
<a id=__codelineno-1-22 name=__codelineno-1-22 href=#__codelineno-1-22></a><span class=w> </span><span class=c1># If no -v, write to stdout.</span>
<a id=__codelineno-1-23 name=__codelineno-1-23 href=#__codelineno-1-23></a><span class=w> </span><span class=nb>printf</span><span class=w> </span>%s<span class=w> </span><span class=s2>&quot;</span><span class=si>${</span><span class=nv>b</span><span class=p>[@]</span><span class=si>}</span><span class=s2>&quot;</span>
<a id=__codelineno-1-24 name=__codelineno-1-24 href=#__codelineno-1-24></a><span class=w> </span><span class=k>fi</span>
<a id=__codelineno-1-25 name=__codelineno-1-25 href=#__codelineno-1-25></a><span class=w> </span><span class=k>fi</span>
</code></pre></div> </div> <p>The remaining examples don't use quite the same tricks, which will hopefully be explained elsewhere eventually. See <a href=../../commands/builtin/unset/#scope>unset</a> for why doing assignments in this way works well.</p> <p>This next example is a variation on <a href=../print_horizontal_line/ >print_horizontal_line</a>. We\'re using the printf field width specifier to truncate the values of a <code>sequence expansion</code> to one character.</p> <div class=highlight><pre><span></span><code><a id=__codelineno-2-1 name=__codelineno-2-1 href=#__codelineno-2-1></a><span class=nv>a</span><span class=o>=({</span>a..z<span class=o>}</span><span class=w> </span><span class=o>{</span>A..Z<span class=o>}</span><span class=w> </span><span class=o>{</span><span class=m>0</span>..9<span class=o>})</span>
<a id=__codelineno-2-2 name=__codelineno-2-2 href=#__codelineno-2-2></a><span class=nb>printf</span><span class=w> </span><span class=s1>&#39;%.1s&#39;</span><span class=w> </span><span class=s2>&quot;</span><span class=si>${</span><span class=nv>a</span><span class=p>[RANDOM%</span><span class=si>${#</span><span class=nv>a</span><span class=p>[@]</span><span class=si>}</span><span class=p>]</span><span class=si>}</span><span class=s2>&quot;</span><span class=o>{</span><span class=m>0</span>..9<span class=o>}</span><span class=w> </span><span class=s1>$&#39;\n&#39;</span>
</code></pre></div> <p>The extra detail that makes this work is to notice that in Bash, <a href=../../syntax/expansion/brace/ >brace expansion</a> is usually the very first type of expansion to be processed, always before parameter expansion. Bash is unique in this respect -- all other shells with a brace expansion feature perform it almost last, just before pathname expansion. First the sequence expansion generates ten parameters, then the parameters are expanded left-to-right causing the <a href=../../syntax/arith_expr/ >arithmetic</a> for each to be evaluated individually, resulting in independent selection of random element of <code>a</code>. To get ten of the same element, put the array selection inside the format string where it will only be evaluated once, just like the dashed-line trick:</p> <div class=highlight><pre><span></span><code><a id=__codelineno-3-1 name=__codelineno-3-1 href=#__codelineno-3-1></a><span class=nb>printf</span><span class=w> </span><span class=s2>&quot;%.s</span><span class=si>${</span><span class=nv>a</span><span class=p>[RANDOM%</span><span class=si>${#</span><span class=nv>a</span><span class=p>[@]</span><span class=si>}</span><span class=p>]</span><span class=si>}</span><span class=s2>&quot;</span><span class=w> </span><span class=o>{</span><span class=m>0</span>..9<span class=o>}</span><span class=w> </span>
</code></pre></div> <p>Selecting random elements whose lengths are not fixed is harder.</p> <div class=highlight><pre><span></span><code><a id=__codelineno-4-1 name=__codelineno-4-1 href=#__codelineno-4-1></a><span class=nv>a</span><span class=o>=(</span>one<span class=w> </span>two<span class=w> </span>three<span class=w> </span>four<span class=w> </span>five<span class=w> </span>six<span class=w> </span>seven<span class=w> </span>eight<span class=w> </span>nine<span class=w> </span>ten<span class=o>)</span>
<a id=__codelineno-4-2 name=__codelineno-4-2 href=#__codelineno-4-2></a><span class=nb>printf</span><span class=w> </span><span class=s1>&#39;%.*s &#39;</span><span class=w> </span><span class=k>$(</span><span class=nb>printf</span><span class=w> </span><span class=s1>&#39;%s &#39;</span><span class=w> </span><span class=s2>&quot;</span><span class=si>${#</span><span class=nv>a</span><span class=p>[x=RANDOM%</span><span class=si>${#</span><span class=nv>a</span><span class=p>[@]</span><span class=si>}</span><span class=p>]</span><span class=si>}</span><span class=s2> </span><span class=si>${</span><span class=nv>a</span><span class=p>[x]</span><span class=si>}</span><span class=s2>&quot;</span><span class=o>{</span><span class=m>1</span>..10<span class=o>}</span><span class=k>)</span>
</code></pre></div> <p>This generates each parameter and it's length in pairs. The \'*\' modifier instructs printf to use the value preceding each parameter as the field width. Note the space between the parameters. This example unfortunately relies upon the unquoted command substitution to perform unsafe wordsplitting so that the outer printf gets each argument. Values in the array can't contain characters in IFS, or anything that might be interpreted as a pattern without using <code>set -f</code>.</p> <p>Lastly, empty brace expansions can be used which don't generate any output that would need to be filtered. The disadvantage of course is that you must construct the brace expansion syntax to add up to the number of arguments to be generated, where the most optimal solution is its set of prime factors.</p> <div class=highlight><pre><span></span><code><a id=__codelineno-5-1 name=__codelineno-5-1 href=#__codelineno-5-1></a><span class=nv>a</span><span class=o>=(</span>one<span class=w> </span>two<span class=w> </span>three<span class=o>)</span>
<a id=__codelineno-5-2 name=__codelineno-5-2 href=#__codelineno-5-2></a><span class=nb>echo</span><span class=w> </span><span class=s2>&quot;</span><span class=si>${</span><span class=nv>a</span><span class=p>[RANDOM%</span><span class=si>${#</span><span class=nv>a</span><span class=p>[@]</span><span class=si>}</span><span class=p>]</span><span class=si>}</span><span class=s2>&quot;</span><span class=o>{</span>,<span class=o>}{</span>,,,,<span class=o>}</span>
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