Difference between revisions of "Dash as /bin/sh"

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[[Category:Arch development (English)]]
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#REDIRECT [[Dash]]
{{expansion}}
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{{accuracy}}
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[http://en.wikipedia.org/wiki/Debian_Almquist_shell Dash] is a minimalist POSIX-complient shell. It can be much faster than Bash, and takes up less memory when in use. Most POSIX compliant scripts specify {{ic|/bin/sh}} at the first line of the script, which means it will run {{ic|/bin/sh}} as the shell, which by default in Arch is a symlink to {{ic|/bin/bash}}.
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You can re-symlink {{ic|/bin/sh}} to {{ic|/bin/dash}}, which can increase system performance, but first you must verify that none of the scripts that aren't explicitly #!/bin/bash scripts are safely POSIX compliant and do not require any of Bash's features.
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This article is for those who want to help [[dash]] become the new {{ic|/bin/sh}}.
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From http://article.gmane.org/gmane.linux.arch.devel/11418:
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*http://mailman.archlinux.org/pipermail/arch-dev-public/2007-November/003053.html
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*https://launchpad.net/ubuntu/+spec/dash-as-bin-sh
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*https://wiki.ubuntu.com/DashAsBinSh
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*All install scripts must be sh-compatible (or we need a way of executing non-sh scripts, there is a bug open for that)
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*Any daemon/init script is probably written for /bin/bash as our rc.conf and other initscripts files use bash arrays, so those need to be pointed correctly
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==Identifying bashisms==
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Features of bash that aren't included in Dash ('bashisms') will not work without being explicitly pointed to {{ic|/bin/bash}}. The following instructions will allow you to find any scripts that may need modification.
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Install {{AUR|checkbashisms}} from the [[AUR]].
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===Common places to check===
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*Installed scripts with a {{Ic|#!/bin/sh}} shebang:
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$ find {,/usr}/bin -type f \
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    -exec grep -q -- '^#!/bin/sh' {} \; \
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    -exec checkbashisms -f -p {} +
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*Package install scripts:
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$ find /var/lib/pacman/local -mindepth 2 -type f -name install \
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    -exec checkbashisms -f -p {} + 2>&1 |\
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    grep -v -e '^you may get strange results' \
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            -e 'does not appear to have a #! interpreter line;$'
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*Initscripts and daemons:
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$ find \
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    /etc/rc.{conf,d,local{,.shutdown},multi,shutdown,single,sysinit} -type -f \
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    -exec checkbashisms -f -p {} + 2>&1 |\
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    grep -v -e '^you may get strange results' \
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            -e 'does not appear to have a #! interpreter line;$'
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==Relinking /bin/sh==
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Once you have verified that it won't break any functionality, it should be safe to relink {{ic|/bin/sh}}. To do so use the following command (as root):
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  ln -sfT /bin/dash /bin/sh
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==Initscript status==
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* The FD checks with {{Ic|test -t}} in {{ic|/etc/rc.d/functions}} do not work correctly with dash, breaking colored output as a result. See http://bugs.archlinux.org/task/19551?project=1&order=id&sort=desc (the patch does not address this issue in particular).
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:* Try using {{Ic|test(1)}} instead of the dash builtin?
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:* Is the problem specific to calls involving {{Ic|init(1)}}?
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Latest revision as of 17:03, 24 October 2013

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