Wednesday, October 3, 2012

#!/bin/bash considered harmful

When one writes a shell script there are a variety of shebang lines that could be used:

  • #!/bin/sh
  • #!/usr/bin/env bash
  • #!/bin/bash

or one of many other options.

Of these only the first two are possibly correct.

Using #!/bin/bash is wrong because:

  • Sometimes bash isn't installed.
  • If it is installed, it may not be in /bin
  • If it is in /bin, the user may have decided to set PATH to use a different installation of bash. Using an absolute path like this overrides the user's choices.
  • bash shouldn't be used for scripts intended for portability

If you have bash specific code use #!/usr/bin/env bash. If you want more portable code try using Debian's checkbashism to find instances of non-POSIX compliant shell scripting.

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