Bash – Test for function’s existence that can work on both bash and zsh

bashfunctionshell-scriptzsh

Is there a way to test whether a shell function exists that will work both for bash and zsh?

Best Answer

If you want to check that there's a currently defined (or at least potentially marked for autoloading) function by the name foo regardless of whether a builtin/executable/keyword/alias may also be available by that name, you could do:

if typeset -f foo > /dev/null; then
  echo there is a foo function
fi

Though note that if there's a keyword or alias called foo as well, it would take precedence over the function (when not quoted).

The above should work in ksh (where it comes from), zsh and bash.

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If you are using the defaults for bash and zsh:

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$ youreditor ~/.zshrc
# Here change your config to:
HISTFILE=~/.bash_history
$ rm ~/.histfile

Now you have the same file for history in both shells.

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Several forms of complex commands such as loops have alternate forms in zsh. These forms are mostly inspired by the C shell, which was fairly common when zsh was young but has now disappeared. These alternate forms act exactly like the normal forms, they're just a different syntax. They're slightly shorter, but less clear.

The standard form for the for command is for x in 1 2 3; do echo $x; done, and the standard form for the while command is while test …; do somecommand; done. Ksh, bash and zsh have an alternate form of for: for ((i = 0; i < 42; i++)); do somecommand; done, which mimics the for loops of languages like Pascal or C, to enumerate integers. Other exotic forms that exist in zsh are specific to zsh (but often inspired by csh).

Best Answer

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