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2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </div> <div class=md-source__repository> flokoe/bash-hackers-wiki </div> </a> </div> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../.. class=md-nav__link> <span class=md-ellipsis> Start </span> </a> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_2> <label class=md-nav__link for=__nav_2 id=__nav_2_label tabindex=0> <span class=md-ellipsis> Commands </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=1 aria-labelledby=__nav_2_label aria-expanded=false> <label class=md-nav__title for=__nav_2> <span class="md-nav__icon md-icon"></span> Commands </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../../commands/classictest/ class=md-nav__link> <span class=md-ellipsis> The classic test command </span> </a> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_2_2> <label class=md-nav__link for=__nav_2_2 id=__nav_2_2_label tabindex=0> <span class=md-ellipsis> Builtin </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=2 aria-labelledby=__nav_2_2_label aria-expanded=false> <label class=md-nav__title for=__nav_2_2> <span class="md-nav__icon md-icon"></span> Builtin </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../../commands/builtin/caller/ class=md-nav__link> <span class=md-ellipsis> The caller builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../../commands/builtin/cd/ class=md-nav__link> <span class=md-ellipsis> The cd builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../../commands/builtin/declare/ class=md-nav__link> <span class=md-ellipsis> The declare builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../../commands/builtin/echo/ class=md-nav__link> <span class=md-ellipsis> The echo builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../../commands/builtin/eval/ class=md-nav__link> <span class=md-ellipsis> The eval builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../../commands/builtin/exec/ class=md-nav__link> <span class=md-ellipsis> The exec builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../../commands/builtin/exit/ class=md-nav__link> <span class=md-ellipsis> The exit builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../../commands/builtin/export/ class=md-nav__link> <span class=md-ellipsis> The export builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../../commands/builtin/kill/ class=md-nav__link> <span class=md-ellipsis> The kill builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../../commands/builtin/let/ class=md-nav__link> <span class=md-ellipsis> The let builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../../commands/builtin/local/ class=md-nav__link> <span class=md-ellipsis> The local builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../../commands/builtin/mapfile/ class=md-nav__link> <span class=md-ellipsis> The mapfile builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../../commands/builtin/printf/ class=md-nav__link> <span class=md-ellipsis> The printf command </span> </a> </li> <li class=md-nav__item> <a href=../../../commands/builtin/read/ class=md-nav__link> <span class=md-ellipsis> The read builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../../commands/builtin/readonly/ class=md-nav__link> <span class=md-ellipsis> The readonly builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../../commands/builtin/return/ class=md-nav__link> <span class=md-ellipsis> The return builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../../commands/builtin/set/ class=md-nav__link> <span class=md-ellipsis> The set builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../../commands/builtin/shift/ class=md-nav__link> <span class=md-ellipsis> The shift builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../../commands/builtin/shopt/ class=md-nav__link> <span class=md-ellipsis> The shopt builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../../commands/builtin/trap/ class=md-nav__link> <span class=md-ellipsis> The trap builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../../commands/builtin/unset/ class=md-nav__link> <span class=md-ellipsis> The unset builtin command </span> </a> </li> <li class=md-nav__item> <a href=../../../commands/builtin/wait/ class=md-nav__link> <span class=md-ellipsis> The wait builtin command </span> </a> </li> </ul> </nav> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_3> <label class=md-nav__link for=__nav_3 id=__nav_3_label tabindex=0> <span class=md-ellipsis> Dict </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=1 aria-labelledby=__nav_3_label aria-expanded=false> <label class=md-nav__title for=__nav_3> <span class="md-nav__icon md-icon"></span> Dict </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../../dict/directory/ class=md-nav__link> <span class=md-ellipsis> Directory </span> </a> </li> <li class=md-nav__item> <a href=../../../dict/end_of_options/ class=md-nav__link> <span class=md-ellipsis> End of Options </span> </a> </li> <li class=md-nav__item> <a href=../../../dict/exit_status/ class=md-nav__link> <span class=md-ellipsis> Exit Status </span> </a> </li> <li class=md-nav__item> <a href=../../../dict/file/ class=md-nav__link> <span class=md-ellipsis> File </span> </a> </li> <li class=md-nav__item> <a href=../../../dict/filetimes/ class=md-nav__link> <span class=md-ellipsis> File timestamp </span> </a> </li> <li class=md-nav__item> <a href=../../../dict/globbing/ class=md-nav__link> <span class=md-ellipsis> Globbing </span> </a> </li> <li class=md-nav__item> <a href=../../../dict/hardlink/ class=md-nav__link> <span class=md-ellipsis> Hardlink </span> </a> </li> <li class=md-nav__item> <a href=../../../dict/interpreter_directive/ class=md-nav__link> <span class=md-ellipsis> Interpreter Directive </span> </a> </li> <li class=md-nav__item> <a href=../../../dict/parameter/ class=md-nav__link> <span class=md-ellipsis> Parameter </span> </a> </li> <li class=md-nav__item> <a href=../../../dict/posix/ class=md-nav__link> <span class=md-ellipsis> POSIX </span> </a> </li> <li class=md-nav__item> <a href=../../../dict/shell/ class=md-nav__link> <span class=md-ellipsis> Shell </span> </a> </li> <li class=md-nav__item> <a href=../../../dict/special_file/ class=md-nav__link> <span class=md-ellipsis> Special file </span> </a> </li> <li class=md-nav__item> <a href=../../../dict/symlink/ class=md-nav__link> <span class=md-ellipsis> Symlink </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_4> <label class=md-nav__link for=__nav_4 id=__nav_4_label tabindex=0> <span class=md-ellipsis> Howto </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=1 aria-labelledby=__nav_4_label aria-expanded=false> <label class=md-nav__title for=__nav_4> <span class="md-nav__icon md-icon"></span> Howto </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../../howto/calculate-dc/ class=md-nav__link> <span class=md-ellipsis> Calculating with dc </span> </a> </li> <li class=md-nav__item> <a href=../../../howto/collapsing_functions/ class=md-nav__link> <span class=md-ellipsis> Collapsing Functions </span> </a> </li> <li class=md-nav__item> <a href=../../../howto/conffile/ class=md-nav__link> <span class=md-ellipsis> Config files for your script </span> </a> </li> <li class=md-nav__item> <a href=../../../howto/dissectabadoneliner/ class=md-nav__link> <span class=md-ellipsis> Dissect a bad oneliner </span> </a> </li> <li class=md-nav__item> <a href=../../../howto/edit-ed/ class=md-nav__link> <span class=md-ellipsis> Editing files via scripts with ed </span> </a> </li> <li class=md-nav__item> <a href=../../../howto/getopts_tutorial/ class=md-nav__link> <span class=md-ellipsis> Small getopts tutorial </span> </a> </li> <li class=md-nav__item> <a href=../../../howto/mutex/ class=md-nav__link> <span class=md-ellipsis> Lock your script (against parallel execution) </span> </a> </li> <li class=md-nav__item> <a href=../../../howto/pax/ class=md-nav__link> <span class=md-ellipsis> pax - the POSIX archiver </span> </a> </li> <li class=md-nav__item> <a href=../../../howto/redirection_tutorial/ class=md-nav__link> <span class=md-ellipsis> Illustrated Redirection Tutorial </span> </a> </li> <li class=md-nav__item> <a href=../../../howto/testing-your-scripts/ class=md-nav__link> <span class=md-ellipsis> Testing your scripts </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_5> <label class=md-nav__link for=__nav_5 id=__nav_5_label tabindex=0> <span class=md-ellipsis> Internals </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=1 aria-labelledby=__nav_5_label aria-expanded=false> <label class=md-nav__title for=__nav_5> <span class="md-nav__icon md-icon"></span> Internals </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../../internals/shell_options/ class=md-nav__link> <span class=md-ellipsis> List of shell options </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_6> <label class=md-nav__link for=__nav_6 id=__nav_6_label tabindex=0> <span class=md-ellipsis> Misc </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=1 aria-labelledby=__nav_6_label aria-expanded=false> <label class=md-nav__title for=__nav_6> <span class="md-nav__icon md-icon"></span> Misc </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../../misc/bashphorisms/ class=md-nav__link> <span class=md-ellipsis> The Bashphorisms </span> </a> </li> <li class=md-nav__item> <a href=../../../misc/readthesourceluke/ class=md-nav__link> <span class=md-ellipsis> Readthesourceluke </span> </a> </li> <li class=md-nav__item> <a href=../../../misc/shell_humor/ class=md-nav__link> <span class=md-ellipsis> Shell Humor </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_7> <label class=md-nav__link for=__nav_7 id=__nav_7_label tabindex=0> <span class=md-ellipsis> Scripting </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=1 aria-labelledby=__nav_7_label aria-expanded=false> <label class=md-nav__title for=__nav_7> <span class="md-nav__icon md-icon"></span> Scripting </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../../scripting/bashbehaviour/ class=md-nav__link> <span class=md-ellipsis> Bash's behaviour </span> </a> </li> <li class=md-nav__item> <a href=../../../scripting/bashchanges/ class=md-nav__link> <span class=md-ellipsis> Bash changes </span> </a> </li> <li class=md-nav__item> <a href=../../../scripting/basics/ class=md-nav__link> <span class=md-ellipsis> The basics of shell scripting </span> </a> </li> <li class=md-nav__item> <a href=../../../scripting/debuggingtips/ class=md-nav__link> <span class=md-ellipsis> Debugging a script </span> </a> </li> <li class=md-nav__item> <a href=../../../scripting/newbie_traps/ class=md-nav__link> <span class=md-ellipsis> Beginner Mistakes </span> </a> </li> <li class=md-nav__item> <a href=../../../scripting/nonportable/ class=md-nav__link> <span class=md-ellipsis> Portability talk </span> </a> </li> <li class=md-nav__item> <a href=../../../scripting/obsolete/ class=md-nav__link> <span class=md-ellipsis> Obsolete and deprecated syntax </span> </a> </li> <li class=md-nav__item> <a href=../../../scripting/posparams/ class=md-nav__link> <span class=md-ellipsis> Handling positional parameters </span> </a> </li> <li class=md-nav__item> <a href=../../../scripting/processtree/ class=md-nav__link> <span class=md-ellipsis> Bash and the process tree </span> </a> </li> <li class=md-nav__item> <a href=../../../scripting/style/ class=md-nav__link> <span class=md-ellipsis> Scripting with style </span> </a> </li> <li class=md-nav__item> <a href=../../../scripting/terminalcodes/ class=md-nav__link> <span class=md-ellipsis> Terminal codes (ANSI/VT100) introduction </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_8> <label class=md-nav__link for=__nav_8 id=__nav_8_label tabindex=0> <span class=md-ellipsis> Snipplets </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=1 aria-labelledby=__nav_8_label aria-expanded=false> <label class=md-nav__title for=__nav_8> <span class="md-nav__icon md-icon"></span> Snipplets </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../../snipplets/ class=md-nav__link> <span class=md-ellipsis> Small code snipplets </span> </a> </li> <li class=md-nav__item> <a href=../../../snipplets/add_color_to_your_scripts/ class=md-nav__link> <span class=md-ellipsis> Add Color to your scripts </span> </a> </li> <li class=md-nav__item> <a href=../../../snipplets/awkcsv/ class=md-nav__link> <span class=md-ellipsis> Using awk to deal with CSV that uses quoted/unquoted delimiters </span> </a> </li> <li class=md-nav__item> <a href=../../../snipplets/filesize/ class=md-nav__link> <span class=md-ellipsis> Show size of a file </span> </a> </li> <li class=md-nav__item> <a href=../../../snipplets/kill_bg_job_without_message/ class=md-nav__link> <span class=md-ellipsis> Kill a background job without a message </span> </a> </li> <li class=md-nav__item> <a href=../../../snipplets/largestfile/ class=md-nav__link> <span class=md-ellipsis> Get largest file </span> </a> </li> <li class=md-nav__item> <a href=../../../snipplets/pause_command/ class=md-nav__link> <span class=md-ellipsis> Pausing a script (like MSDOS pause command) </span> </a> </li> <li class=md-nav__item> <a href=../../../snipplets/prargs/ class=md-nav__link> <span class=md-ellipsis> Print argument list for testing </span> </a> </li> <li class=md-nav__item> <a href=../../../snipplets/print_horizontal_line/ class=md-nav__link> <span class=md-ellipsis> Print a horizontal line </span> </a> </li> <li class=md-nav__item> <a href=../../../snipplets/rndstr/ class=md-nav__link> <span class=md-ellipsis> Print a random string or select random elements </span> </a> </li> <li class=md-nav__item> <a href=../../../snipplets/screen_saverestore/ class=md-nav__link> <span class=md-ellipsis> Save and restore terminal/screen content </span> </a> </li> <li class=md-nav__item> <a href=../../../snipplets/ssh_fetchkeys/ class=md-nav__link> <span class=md-ellipsis> Fetching SSH hostkeys without interaction </span> </a> </li> <li class=md-nav__item> <a href=../../../snipplets/ssh_local_var/ class=md-nav__link> <span class=md-ellipsis> Run some bash commands with SSH remotely using local variables </span> </a> </li> <li class=md-nav__item> <a href=../../../snipplets/wrapperargs/ class=md-nav__link> <span class=md-ellipsis> Generate code with own arguments properly quoted </span> </a> </li> <li class=md-nav__item> <a href=../../../snipplets/xclip/ class=md-nav__link> <span class=md-ellipsis> X-Clipboard on Commandline </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--active md-nav__item--section md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_9 checked> <label class=md-nav__link for=__nav_9 id=__nav_9_label tabindex> <span class=md-ellipsis> Syntax </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=1 aria-labelledby=__nav_9_label aria-expanded=true> <label class=md-nav__title for=__nav_9> <span class="md-nav__icon md-icon"></span> Syntax </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../arith_expr/ class=md-nav__link> <span class=md-ellipsis> Arithmetic expressions </span> </a> </li> <li class=md-nav__item> <a href=../../arrays/ class=md-nav__link> <span class=md-ellipsis> Arrays </span> </a> </li> <li class=md-nav__item> <a href=../../basicgrammar/ class=md-nav__link> <span class=md-ellipsis> Basic grammar rules of Bash </span> </a> </li> <li class=md-nav__item> <a href=../../pattern/ class=md-nav__link> <span class=md-ellipsis> Patterns and pattern matching </span> </a> </li> <li class=md-nav__item> <a href=../../pe/ class=md-nav__link> <span class=md-ellipsis> Parameter expansion </span> </a> </li> <li class=md-nav__item> <a href=../../quoting/ class=md-nav__link> <span class=md-ellipsis> Quotes and escaping </span> </a> </li> <li class=md-nav__item> <a href=../../redirection/ class=md-nav__link> <span class=md-ellipsis> Redirection </span> </a> </li> <li class=md-nav__item> <a href=../../shellvars/ class=md-nav__link> <span class=md-ellipsis> Special parameters and shell variables </span> </a> </li> <li class=md-nav__item> <a href=../../words/ class=md-nav__link> <span class=md-ellipsis> Words... </span> </a> </li> <li class="md-nav__item md-nav__item--active md-nav__item--section md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_9_10 checked> <label class=md-nav__link for=__nav_9_10 id=__nav_9_10_label tabindex> <span class=md-ellipsis> Ccmd </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=2 aria-labelledby=__nav_9_10_label aria-expanded=true> <label class=md-nav__title for=__nav_9_10> <span class="md-nav__icon md-icon"></span> Ccmd </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../arithmetic_eval/ class=md-nav__link> <span class=md-ellipsis> Arithmetic evaluation (command) </span> </a> </li> <li class=md-nav__item> <a href=../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=../case/ class=md-nav__link> <span class=md-ellipsis> The case statement </span> </a> </li> <li class=md-nav__item> <a href=../classic_for/ class=md-nav__link> <span class=md-ellipsis> The classic for-loop </span> </a> </li> <li class="md-nav__item md-nav__item--active"> <input class="md-nav__toggle md-toggle" type=checkbox id=__toc> <label class="md-nav__link md-nav__link--active" for=__toc> <span class=md-ellipsis> The conditional expression </span> <span class="md-nav__icon md-icon"></span> </label> <a href=./ class="md-nav__link md-nav__link--active"> <span class=md-ellipsis> The conditional expression </span> </a> <nav class="md-nav md-nav--secondary" aria-label="Table of contents"> <label class=md-nav__title for=__toc> <span class="md-nav__icon md-icon"></span> Table of contents </label> <ul class=md-nav__list data-md-component=toc data-md-scrollfix> <li class=md-nav__item> <a href=#synopsis class=md-nav__link> <span class=md-ellipsis> Synopsis </span> </a> </li> <li class=md-nav__item> <a href=#description class=md-nav__link> <span class=md-ellipsis> Description </span> </a> <nav class=md-nav aria-label=Description> <ul class=md-nav__list> <li class=md-nav__item> <a href=#word-splitting class=md-nav__link> <span class=md-ellipsis> Word splitting </span> </a> </li> <li class=md-nav__item> <a href=#regular-expression-matching class=md-nav__link> <span class=md-ellipsis> Regular Expression Matching </span> </a> <nav class=md-nav aria-label="Regular Expression Matching"> <ul class=md-nav__list> <li class=md-nav__item> <a href=#the-special-bash_rematch-array-variable class=md-nav__link> <span class=md-ellipsis> The special BASH_REMATCH array variable </span> </a> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=#behaviour-differences-compared-to-the-builtin-test-command class=md-nav__link> <span class=md-ellipsis> Behaviour differences compared to the builtin test command </span> </a> </li> <li class=md-nav__item> <a href=#implicit-arithmetic-context class=md-nav__link> <span class=md-ellipsis> Implicit arithmetic context </span> </a> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=#examples class=md-nav__link> <span class=md-ellipsis> Examples </span> </a> </li> <li class=md-nav__item> <a href=#portability-considerations class=md-nav__link> <span class=md-ellipsis> Portability considerations </span> </a> </li> <li class=md-nav__item> <a href=#see-also class=md-nav__link> <span class=md-ellipsis> See also </span> </a> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=../grouping_plain/ class=md-nav__link> <span class=md-ellipsis> Grouping commands </span> </a> </li> <li class=md-nav__item> <a href=../grouping_subshell/ class=md-nav__link> <span class=md-ellipsis> Grouping commands in a subshell </span> </a> </li> <li class=md-nav__item> <a href=../if_clause/ class=md-nav__link> <span class=md-ellipsis> The if-clause </span> </a> </li> <li class=md-nav__item> <a href=../intro/ class=md-nav__link> <span class=md-ellipsis> Bash compound commands </span> </a> </li> <li class=md-nav__item> <a href=../until_loop/ class=md-nav__link> <span class=md-ellipsis> The until loop </span> </a> </li> <li class=md-nav__item> <a href=../user_select/ class=md-nav__link> <span class=md-ellipsis> User selections </span> </a> </li> <li class=md-nav__item> <a href=../while_loop/ class=md-nav__link> <span class=md-ellipsis> The while-loop </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--section md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_9_11> <label class=md-nav__link for=__nav_9_11 id=__nav_9_11_label tabindex> <span class=md-ellipsis> Expansion </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=2 aria-labelledby=__nav_9_11_label aria-expanded=false> <label class=md-nav__title for=__nav_9_11> <span class="md-nav__icon md-icon"></span> Expansion </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../expansion/arith/ class=md-nav__link> <span class=md-ellipsis> Arithmetic expansion </span> </a> </li> <li class=md-nav__item> <a href=../../expansion/brace/ class=md-nav__link> <span class=md-ellipsis> Brace expansion </span> </a> </li> <li class=md-nav__item> <a href=../../expansion/cmdsubst/ class=md-nav__link> <span class=md-ellipsis> Command substitution </span> </a> </li> <li class=md-nav__item> <a href=../../expansion/globs/ class=md-nav__link> <span class=md-ellipsis> Pathname expansion (globbing) </span> </a> </li> <li class=md-nav__item> <a href=../../expansion/intro/ class=md-nav__link> <span class=md-ellipsis> Expansions and substitutions </span> </a> </li> <li class=md-nav__item> <a href=../../expansion/proc_subst/ class=md-nav__link> <span class=md-ellipsis> Process substitution </span> </a> </li> <li class=md-nav__item> <a href=../../expansion/tilde/ class=md-nav__link> <span class=md-ellipsis> Tilde expansion </span> </a> </li> <li class=md-nav__item> <a href=../../expansion/wordsplit/ class=md-nav__link> <span class=md-ellipsis> Word splitting </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--section md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_9_12> <label class=md-nav__link for=__nav_9_12 id=__nav_9_12_label tabindex> <span class=md-ellipsis> Grammar </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=2 aria-labelledby=__nav_9_12_label aria-expanded=false> <label class=md-nav__title for=__nav_9_12> <span class="md-nav__icon md-icon"></span> Grammar </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../grammar/parser_exec/ class=md-nav__link> <span class=md-ellipsis> Parser exec </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--section md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_9_13> <label class=md-nav__link for=__nav_9_13 id=__nav_9_13_label tabindex> <span class=md-ellipsis> Keywords </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=2 aria-labelledby=__nav_9_13_label aria-expanded=false> <label class=md-nav__title for=__nav_9_13> <span class="md-nav__icon md-icon"></span> Keywords </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../keywords/coproc/ class=md-nav__link> <span class=md-ellipsis> The coproc keyword </span> </a> </li> </ul> </nav> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=../../../tags/ class=md-nav__link> <span class=md-ellipsis> Tags </span> </a> </li> </ul> </nav> </div> </div> </div> <div class="md-sidebar md-sidebar--secondary" data-md-component=sidebar data-md-type=toc> <div class=md-sidebar__scrollwrap> <div class=md-sidebar__inner> <nav class="md-nav md-nav--secondary" aria-label="Table of contents"> <label class=md-nav__title for=__toc> <span class="md-nav__icon md-icon"></span> Table of contents </label> <ul class=md-nav__list data-md-component=toc data-md-scrollfix> <li class=md-nav__item> <a href=#synopsis class=md-nav__link> <span class=md-ellipsis> Synopsis </span> </a> </li> <li class=md-nav__item> <a href=#description class=md-nav__link> <span class=md-ellipsis> Description </span> </a> <nav class=md-nav aria-label=Description> <ul class=md-nav__list> <li class=md-nav__item> <a href=#word-splitting class=md-nav__link> <span class=md-ellipsis> Word splitting </span> </a> </li> <li class=md-nav__item> <a href=#regular-expression-matching class=md-nav__link> <span class=md-ellipsis> Regular Expression Matching </span> </a> <nav class=md-nav aria-label="Regular Expression Matching"> <ul class=md-nav__list> <li class=md-nav__item> <a href=#the-special-bash_rematch-array-variable class=md-nav__link> <span class=md-ellipsis> The special BASH_REMATCH array variable </span> </a> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=#behaviour-differences-compared-to-the-builtin-test-command class=md-nav__link> <span class=md-ellipsis> Behaviour differences compared to the builtin test command </span> </a> </li> <li class=md-nav__item> <a href=#implicit-arithmetic-context class=md-nav__link> <span class=md-ellipsis> Implicit arithmetic context </span> </a> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=#examples class=md-nav__link> <span class=md-ellipsis> Examples </span> </a> </li> <li class=md-nav__item> <a href=#portability-considerations class=md-nav__link> <span class=md-ellipsis> Portability considerations </span> </a> </li> <li class=md-nav__item> <a href=#see-also class=md-nav__link> <span class=md-ellipsis> See also </span> </a> </li> </ul> </nav> </div> </div> </div> <div class=md-content data-md-component=content> <article class="md-content__inner md-typeset"> <a href=https://github.com/flokoe/bash-hackers-wiki/edit/main/docs/syntax/ccmd/conditional_expression.md title="Edit this page" class="md-content__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M10 20H6V4h7v5h5v3.1l2-2V8l-6-6H6c-1.1 0-2 .9-2 2v16c0 1.1.9 2 2 2h4zm10.2-7c.1 0 .3.1.4.2l1.3 1.3c.2.2.2.6 0 .8l-1 1-2.1-2.1 1-1c.1-.1.2-.2.4-.2m0 3.9L14.1 23H12v-2.1l6.1-6.1z"/></svg> </a> <a href=https://github.com/flokoe/bash-hackers-wiki/raw/main/docs/syntax/ccmd/conditional_expression.md title="View source of this page" class="md-content__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M17 18c.56 0 1 .44 1 1s-.44 1-1 1-1-.44-1-1 .44-1 1-1m0-3c-2.73 0-5.06 1.66-6 4 .94 2.34 3.27 4 6 4s5.06-1.66 6-4c-.94-2.34-3.27-4-6-4m0 6.5a2.5 2.5 0 0 1-2.5-2.5 2.5 2.5 0 0 1 2.5-2.5 2.5 2.5 0 0 1 2.5 2.5 2.5 2.5 0 0 1-2.5 2.5M9.27 20H6V4h7v5h5v4.07c.7.08 1.36.25 2 .49V8l-6-6H6a2 2 0 0 0-2 2v16a2 2 0 0 0 2 2h4.5a8.2 8.2 0 0 1-1.23-2"/></svg> </a> <h1 id=the-conditional-expression>The conditional expression<a class=headerlink href=#the-conditional-expression title="Permanent link">¶</a></h1> <h2 id=synopsis>Synopsis<a class=headerlink href=#synopsis title="Permanent link">¶</a></h2> <div class=highlight><pre><span></span><code>[[ <EXPRESSION> ]]
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</code></pre></div> <h2 id=description>Description<a class=headerlink href=#description title="Permanent link">¶</a></h2> <p>The conditional expression is meant as the modern variant of the <a href=../../../commands/classictest/ >classic test command</a>. Since it is <strong>not</strong> a normal command, Bash doesn't need to apply the normal commandline parsing rules like recognizing <code>&&</code> as <a href=../../basicgrammar/#lists>command list</a> operator.</p> <p>The testing features basically are the same (see the lists for <a href=../../../commands/classictest/ >classic test command</a>), with some additions and extensions.</p> <table> <thead> <tr> <th>Operator</th> <th>Description</th> </tr> </thead> <tbody> <tr> <td><code>( <EXPRESSION> )</code></td> <td>Used to group expressions, to influence precedence of operators</td> </tr> <tr> <td><code><EXPRESSION1> && <EXPRESSION2></code></td> <td><code>TRUE</code> if <code><EXPRESSION1></code><strong>and</strong><code><EXPRESSION2></code> are <code>TRUE</code> (do <strong>not</strong> use <code>-a</code>!)</td> </tr> <tr> <td><code><EXPRESSION1>||<EXPRESSION2></code></td> <td><code>TRUE</code> if <code><EXPRESSION1></code><strong>or</strong><code><EXPRESSION2></code> is <code>TRUE</code> (do <strong>not</strong> use <code>-o</code>!)</td> </tr> <tr> <td><code><STRING> == <PATTERN></code></td> <td><code><STRING></code> is checked against the pattern <code><PATTERN></code> - <code>TRUE</code> on a match<br><em>But note¹, quoting the pattern forces a literal comparison.</em></td> </tr> <tr> <td><code><STRING> = <PATTERN></code></td> <td>equivalent to the <code>==</code> operator</td> </tr> <tr> <td><code><STRING> != <PATTERN></code></td> <td><code><STRING></code> is checked against the pattern <code><PATTERN></code> - <code>TRUE</code> on <strong>no match</strong></td> </tr> <tr> <td><code><STRING> =~ <ERE></code></td> <td><code><STRING></code> is checked against the <a href=https://en.wikipedia.org/wiki/Regular_expression#POSIX_extended>extended regular expression</a> <code><ERE></code> - <code>TRUE</code> on a match</td> </tr> <tr> <td>See the <a href=../../../commands/classictest/#file_tests>classic test operators</a></td> <td>Do <strong>not</strong> use the <code>test</code>-typical operators <code>-a</code> and <code>-o</code> for AND and OR.</td> </tr> <tr> <td>See also <a href=../../arith_expr/#comparisons>arithmetic comparisons</a></td> <td>Using <code>(( <EXPRESSION> ))</code>, the <a href=../arithmetic_eval/ >arithmetic expression compound command</a></td> </tr> </tbody> </table> <p>When the <code>==</code> and <code>!=</code> operators are used, the string to the right of the operator is considered a pattern and matched according to the rules of <a href=../../pattern/ >Pattern Matching</a>. If the shell option <code>nocasematch</code> is enabled, the match is performed without regard to the case of alphabetic characters.</p> <p>¹Any part of the pattern may be quoted to force it to be matched as a literal string.</p> <p>When the operators <code><</code> and <code>></code> are used (string collation order), the test happens using the current locale when the <code>compat</code> level is greater than "40".</p> <p>Operator precedence (highest => lowest):</p> <ul> <li><code>( <EXPRESSION> )</code></li> <li><code>! <EXPRESSION></code></li> <li><code><EXPRESSION1> && <EXPRESSION2></code></li> <li><code><EXPRESSION1> || <EXPRESSION2></code></li> </ul> <p>Do <strong>not</strong> use the <code>test</code>-typical operators <code>-a</code> and <code>-o</code> for AND and OR, they are not known to the conditional expression. Instead, use the operators <code>&&</code> and <code>||</code>.</p> <h3 id=word-splitting>Word splitting<a class=headerlink href=#word-splitting title="Permanent link">¶</a></h3> <p><a href=../../expansion/wordsplit/ >Word splitting</a> and <a href=../../expansion/globs/ >pathname expansion</a> are not performed in the expression you give. That means, a variable containing spaces can be used without quoting:</p> <div class=highlight><pre><span></span><code>sentence="Be liberal in what you accept, and conservative in what you send"
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checkme="Be liberal in what you accept, and conservative in what you send"
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if [[ $sentence == $checkme ]]; then
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echo "Matched...!"
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else
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echo "Sorry, no match :-("
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fi
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</code></pre></div> <p>Compare that to the <a href=../../../commands/classictest/ >classic test command</a>, where word splitting is done (because it's a normal command, not something special):</p> <div class=highlight><pre><span></span><code>sentence="Be liberal in what you accept, and conservative in what you send"
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checkme="Be liberal in what you accept, and conservative in what you send"
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if [ "$sentence" == "$checkme" ]; then
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echo "Matched...!"
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else
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echo "Sorry, no match :-("
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fi
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</code></pre></div> <p>You need to quote that variable reference in the classic test command, since (due to the spaces) the word splitting will break it otherwise!</p> <h3 id=regular-expression-matching>Regular Expression Matching<a class=headerlink href=#regular-expression-matching title="Permanent link">¶</a></h3> <p>Using the operator <code>=~</code>, the left hand side operand is matched against the <strong>extended regular expression (ERE)</strong> on the right hand side.</p> <p>This is consistent with matching against patterns: Every quoted part of the regular expression is taken literally, even if it contains regular expression special characters.</p> <p>Best practise is to put the regular expression to match against into a variable. This is to avoid shell parsing errors on otherwise valid regular expressions.</p> <div class=highlight><pre><span></span><code>REGEX="^[[:upper:]]{2}[[:lower:]]*$"
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# Test 1
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STRING=Hello
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if [[ $STRING =~ $REGEX ]]; then
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echo "Match."
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else
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echo "No match."
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fi
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# ==> "No match."
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# Test 2
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STRING=HEllo
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if [[ $STRING =~ $REGEX ]]; then
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echo "Match."
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else
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echo "No match."
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fi
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# ==> "Match."
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</code></pre></div> <p>The interpretation of quoted regular expression special characters can be influenced by setting the <code>compat31</code> and <code>compat32</code> shell options (<code>compat*</code> in general). See <a href=../../../internals/shell_options/ >shell_options</a>.</p> <h4 id=the-special-bash_rematch-array-variable>The special BASH_REMATCH array variable<a class=headerlink href=#the-special-bash_rematch-array-variable title="Permanent link">¶</a></h4> <p>An array variable whose members are assigned by the <code>=~</code> binary operator to the <code>[[</code> conditional command.</p> <p>The element with index 0 is the portion of the string matching the entire regular expression. The element with index n is the portion of the string matching the nth parenthesized subexpression.</p> <p>See <a href=../../shellvars/#bash_rematch>BASH_REMATCH</a>.</p> <p>Example:</p> <div class=highlight><pre><span></span><code>if [[ "The quick, red fox" =~ ^The\ (.*),\ (.*)\ fox$ ]]; then
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echo "${BASH_REMATCH[0]} is ${BASH_REMATCH[1]} and ${BASH_REMATCH[2]}.";
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fi
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==> The quick, red fox is quick and red.
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</code></pre></div> <h3 id=behaviour-differences-compared-to-the-builtin-test-command>Behaviour differences compared to the builtin test command<a class=headerlink href=#behaviour-differences-compared-to-the-builtin-test-command title="Permanent link">¶</a></h3> <p>As of Bash 4.1 alpha, the test primaries '<' and '>' (compare strings lexicographically) use the current locale settings, while the same primitives for the builtin test command don't. This leads to the following situation where they behave differently:</p> <div class=highlight><pre><span></span><code>$ ./cond.sh
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[[ ' 4' < '1' ]] --> exit 1
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[[ 'step+' < 'step-' ]] --> exit 1
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[ ' 4' < '1' ] --> exit 0
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[ 'step+' < 'step-' ] --> exit 0
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</code></pre></div> <p>It won't be aligned. The conditional expression continues to respect the locate, as introduced with 4.1-alpha, the builtin <code>test</code>/<code>[</code> command continues to behave differently.</p> <h3 id=implicit-arithmetic-context>Implicit arithmetic context<a class=headerlink href=#implicit-arithmetic-context title="Permanent link">¶</a></h3> <p>When you use a numeric comparison, the arguments are evaluated as an arithmetic expression. The arithmetic expression must be quoted if it both contains whitespace and is not the result of an expansion.</p> <div class=highlight><pre><span></span><code>[[ 'i=5, i+=2' -eq 3+4 ]] && echo true # prints true.
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</code></pre></div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">¶</a></h2> <h2 id=portability-considerations>Portability considerations<a class=headerlink href=#portability-considerations title="Permanent link">¶</a></h2> <ul> <li><code>[[ ... ]]</code> functionality isn't specified by POSIX(R), though it's a reserved word</li> <li>Amongst the major "POSIX-shell superset languages" (for lack of a better term) which do have <code>[[</code>, the test expression compound command is one of the very most portable non-POSIX features. Aside from the <code>=~</code> operator, almost every major feature is consistent between Ksh88, Ksh93, mksh, Zsh, and Bash. Ksh93 also adds a large number of unique pattern matching features not supported by other shells including support for several different regex dialects, which are invoked using a different syntax from Bash's <code>=~</code>, though <code>=~</code> is still supported by ksh and defaults to ERE.</li> <li>As an extension to POSIX ERE, most GNU software supports backreferences in ERE, including Bash. According to POSIX, only BRE is supposed to support them. This requires Bash to be linked against glibc, so it won't necessarily work on all platforms. For example, <code>$(m='(abc(def))(\1)(\2)'; [[ abcdefabcdefdef =~ $m ]]; printf '<%s> ' $? "${BASH_REMATCH[@]}" )</code> will give <code><0> <abcdefabcdefdef> <abcdef> <def> <abcdef> <def></code>.</li> <li>the <code>=~</code> (regex) operator was introduced in Bash 3.0, and its behaviour changed in Bash 3.2: since 3.2, quoted strings and substrings are matched as literals by default.</li> <li>the behaviour of the <code><</code> and <code>></code> operators (string collation order) has changed since Bash 4.0</li> </ul> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">¶</a></h2> <ul> <li>Internal: <a href=../../pattern/ >pattern matching language</a></li> <li>Internal: <a href=../../../commands/classictest/ >the classic test command</a></li> <li>Internal: <a href=../if_clause/ >the if-clause</a></li> <li><a href=http://mywiki.wooledge.org/BashFAQ/031>What is the difference between test, [ and [[ ?</a> - BashFAQ 31 - Greg's wiki.</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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