Check if a given function name exists in a sourced shell script file

Question

In Bash I can use $(type -t function_name) = "function" to check if the function by name function_name exists or not in a sourced file which is sourced using source file_name command. I'm trying to achieve the same in ksh where the source command equivalent is .. But I'm stuck with type -t syntax for which I'm getting the below error in ksh.

abc.sh in Bash

source def.sh
if [ "$(type -t foo)" != "function" ]; then
    echo "function foo exists"
fi

abc.sh in Korn

. def.sh
if [ "$(type -t foo)" != "function" ]; then
    echo "function foo exists"
fi

Error in Korn shell

./abc.sh[4]: whence: -t: unknown option

ksh version

echo $KSH_VERSION
@(#)PD KSH v5.2.14 99/07/13.2

Answer 1

Even a bit simpler and without a subshell:

foo(){
  echo "foo"
}

if typeset -f foo >/dev/null 2>&1; then
    echo "function foo exists"
fi

In bash, typeset and declare are exactly the same. The only difference is that typeset is considered obsolete.

...

typeset is portable to some other shells, for example, ksh93. If you are aiming for cross-shell portability, use typeset (and make sure that the way you are calling it is portable). If you don't care about such portability, use declare.

• What is the difference between declare and typeset?

• Difference between typeset and declare:

The former is more portable(e.g. ksh), while the latter is more preferable when portability is not a concern.

• Differences between declare, typeset and local variable in Bash

Answer 2

I'd love to go with typeset +f, which prints all defined function names in ksh, zsh; but bash is special and wants to use -F instead. So, either you write a detection function that does different things based on what shell you have (and you'd simply test that by defining a function, and checking what works, and then using that method to check the function name you actually wanted to check), or you jump through a bit of parsing hoops.

typeset -f functionname gives you the definition of functionname if a function of that name exists. So, deal with that!

functionname="foo"

if [ -n "$(typeset -f $functionname)" ]; then
   printf '%s is defined.\n' "$functionname"
fi