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Debian GNU/Linux Reference Guide
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13.2.2 POSIX shells

Several packages provide a POSIX shell in Debian:

  • dash (Sarge)

    • Priority: optional

    • Installed-Size: 176

    • Smallest and fastest by far – best for initial boot

  • ash (Woody)

    • Priority: optional

    • Installed-Size: 180

    • Smaller and much faster – good for initial boot

  • bash

    • Essential: yes

    • Priority: required

    • Installed-Size: 580

    • Larger and featureful – many extensions implemented

  • pdksh

    • Priority: optional

    • Installed-Size: 408

    • Complete AT&T ksh look-alike

If you are writing a shell script for portability, it is best to write it as a POSIX shell script. Use /bin/sh linked to ash (or dash) to test its POSIX compliance. Avoid writing scripts with "bashisms" or the "zshisms". For example, avoid:

  • if [ foo == bar ] ; then ...

  • diff -u file.c{.orig,}

  • mkdir /foo{bar,baz}

The description for the shell in this document applies only for the POSIX type shells and thus does not apply for the csh type shells including tcsh.


Debian GNU/Linux Reference Guide
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