Finding bash Portably for #!
Problem
You need to run a bash script on several machines, but bash is not always in the same place. See Getting bash for xBSD.
Solution
Use the /usr/bin/env command in the shebang line, as in #!/usr/bin/env bash
. If your system doesn’t
have env in /usr/bin, ask your
system administrator to install it, move it, or create a symbolic link
because this is the required location. For example, Red Hat inexplicably uses /bin/env,
but they at least create a symlink to the correct location.
You could also create symbolic links for bash itself, but using env is the canonical and correct solution.
Discussion
env’s purpose is to “run a program in a modified environment,” but since it will search the path for the command it is given to run, it works very well for this use.
You may be tempted to use #!/bin/sh
instead.
Don’t. If you are using bash-specific features in
your script, they will not work on machines that do not use
bash in Bourne shell mode for
/bin/sh (e.g., BSD, Solaris, Ubuntu 6.10+). And even if you aren’t using
bash-specific features now, you may forget about
that in the future. If you are committed to using only POSIX features, by all means use #!/bin/sh
(and don’t develop on Linux, see
Developing Portable Shell Scripts), but otherwise be
specific.
You may sometimes see a space between #!
and /bin/whatever
. Historically there were some systems that required the space, though in practice we haven’t seen one in a long time. It’s very unlikely any system running ...
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