Bash Function

Declaration

A function is declared with one of:

myfunction() {
  :
}

function myfunction() {
  :
}

If the function keyword is used, the parentheses are optional.

Usage

The above functions would be called like:

myfunction "first argument" "second argument"

Arguments

Arguments passed to a function implicitly overwrite the positional variables ($1, $2, and so on) as well as the argument count variable ($#). All of these will be reset to the original values upon the function's return.

Note that $0 is not overwritten.

Local Scope

To mark a variable as belonging only to a function's scope, declare it with the local builtin.

local x=y

Error and Return Codes

By default a function does not set the exit code. But it also does not clear the code. The final command in a function effectively sets the error code for the function as well.

The return builtin causes the function to return immediately with a specified exit code.

isdirectory() {
  if [ -d "$1" ]; then
    return 0
  else
    return 1
  fi
}

if isdirectory "$some_directory"; then
  :
fi

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