Bash function returns unexpected value

Question

function() {
   if something_that_will_fail; then
      irrelevantcode
   else
      echo "should be here"
      false
   fi
}

echo $function

This outputs "should be here". How do I get the false value?

false is a command that always has an exit status of 1, not a value. — chepner
– chepner, Commented Mar 16, 2020 at 17:36
Also, note that the function's exit status will be that of the last command in it. In this case, it's false, so the function will exit with a status of 1 (indicating failure), but if the function does anything after the false command, that status will change. That's why it's better to use something like return 1 to control the function's exit status; return, by definition, is the last thing the function will execute, so it has complete control over the exit status. — Gordon Davisson
– Gordon Davisson, Commented Mar 16, 2020 at 18:03

choroba · Accepted Answer · 2020-03-16 17:26:13Z

1

You seem to be confusing the output with returned value.

$function is a variable, you don't seem to populate it anywhere. To populate it with the output of the function, use

output=$(function_call)

The return value of a function can be retrieved from the special variable $?.

function_call
value=$?

If you want to use it in a condition, you often don't need the variable at all, as you can run the function directly in the condition:

function_call
if (( $? )) ; then
    echo There was an error
else
    echo Everything OK
fi

can be shortened to

if function_call ; then
    echo Everything OK
else
    echo There was an error
fi

answered Mar 16, 2020 at 17:26

choroba

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Comments

Kenan Güler · Accepted Answer · 2020-03-16 18:37:14Z

Bash has no built-in boolean variables. Further, calling a function a la $function_name also seems wrong to me.

I am not sure, what you are trying to achieve, but you have two options there:

You can output strings within your function and retrieve them afterwards.
Additionally, you can also set the exit status of your function via the return key (this is what return is all about); here you can also specify a status code within a range 0-255 for your return, where 0 indicates that function terminated successfully, and all other numbers indicate the opposite.

Example:

#!/usr/bin/env bash

function is_greater() {
   local value1=$1     
   local value2=$2

   if [[ $value1 -gt $value2 ]]; then
        printf "%s is greater than %s! \n" $value1 $value2
        return 0
   else 
        printf "%s is NOT greater than %s! \n" $value1 $value2
        return 1
   fi
}

what_func_says=$(is_greater 21 42)
func_exit_status=$?

if [[ $func_exit_status -eq 0 ]]; then
  echo $what_func_says
  printf "success code: %s \n" $func_exit_status
else
  echo $what_func_says
  printf "error code: %s \n" $func_exit_status
fi

Output:

21 is NOT greater than 42!
error code: 1

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