Editing Bash (Unix shell) (section)

=== Portability with POSIX ===
Invoking Bash with the <code>--posix</code> option or stating <code>set -o posix</code> in a script causes Bash to conform very closely with the [[Posix#POSIX.2|POSIX 1003.2 standard]].<ref name="tldp">{{Cite web |last=Mendel Cooper     |title=Portability Issues     |url=http://tldp.org/LDP/abs/html/portabilityissues.html     |url-status=live     |archive-url=https://web.archive.org/web/20120127105451/http://tldp.org/LDP/abs/html/portabilityissues.html     |archive-date=January 27, 2012     |access-date=January 26, 2012     |website=The Linux Documentation Project   |publisher=ibiblio.org    }}</ref> Bash shell scripts intended for [[portability (computer science)|portability]] should take into account at least the POSIX shell standard. Some bash features not found in POSIX are:<ref name="tldp" /><ref name="deb">{{Cite web |title=10. Files     |url=https://www.debian.org/doc/debian-policy/ch-files.html#scripts     |url-status=live     |archive-url=https://web.archive.org/web/20200512050159/https://www.debian.org/doc/debian-policy/ch-files.html#scripts     |archive-date=May 12, 2020     |access-date=May 11, 2020     |website=Debian Policy Manual v4.5.0.2  }}</ref>

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* Certain extended invocation options
* Brace expansion
* Arrays and associative arrays
* The double bracket {{code| [[...]] }} extended test construct and its regex matching
* The double-parentheses arithmetic-evaluation construct (only {{code|(( ... ))}}; {{code|$(( ... ))}} is POSIX)
* Certain string-manipulation operations in parameter expansion
* {{code|local}} for scoped variables
* Process substitution
* Bash-specific builtins
* [[Coprocess]]es
* $EPOCHSECONDS and $EPOCHREALTIME variables<ref>{{Cite web |title=How To Format Date And Time In Linux, MacOS, And Bash?     |url=https://www.shell-tips.com/linux/how-to-format-date-and-time-in-linux-macos-and-bash/#using-the-gnu-date-command-line     |url-status=live     |archive-url=https://web.archive.org/web/20200603230615/https://www.shell-tips.com/linux/how-to-format-date-and-time-in-linux-macos-and-bash/#using-the-gnu-date-command-line     |archive-date=June 3, 2020     |access-date=June 3, 2020     |website=Shell Tips!  }}</ref>
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If a piece of code uses such a feature, it is called a "bashism" – a problem for portable use. Debian's {{code|checkbashisms}} and Vidar Holen's {{code|shellcheck}} can be used to make sure that a script does not contain these parts.<ref name="checkbashisms, ManKier man page">{{man|1|checkbashisms|ManKier}}</ref><ref name="shellcheck, ManKier man page">{{man|1|shellcheck|ManKier}}</ref> The list varies depending on the actual target shell: Debian's policy allows some extensions in their scripts (as they are in the [[Almquist shell#Dash|dash]] shell),<ref name=deb/> while a script intending to support pre-POSIX Bourne shells, like [[autoconf]]'s {{code|configure}}, are even more limited in the features they can use.<ref>{{Cite web |title=Portable Shell     |url=https://www.gnu.org/software/autoconf/manual/html_node/Portable-Shell.html     |url-status=live     |archive-url=https://web.archive.org/web/20210302212413/https://www.gnu.org/savannah-checkouts/gnu/autoconf/manual/autoconf-2.70/html_node/Portable-Shell.html     |archive-date=March 2, 2021     |access-date=20 January 2020     |website=Autoconf  }}</ref>

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