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AbstProcDo
Asked: 2018-04-14 20:58:15 +0800 CST

Is `return` within function a compulsory requirement?

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The the simpler form of a function is:

name () { commands return }

I find no difference in a function with and without return.
Suppose the minimal code:

step_forward (){
    echo "step one;"
    return
}
turn_around() {
    echo "turn around."
    return
}

step_forward
turn_around

Run and check the exit status:

$ bash testing.sh
step one;
turn around.
$ echo $?
0

Run it again after commenting out return

$ bash testing.sh
step one;
turn around.
$ echo $?
0

In what circumstances should a function end with a return?

bash

1 Answers

  1. Best Answer

    A return value is not required in a function. Normally a return would be used in a script for an exit value to be returned. Exit values are normally like a 1 or a 0 where a lot of scripters might use it for a 0 as successful and a 1 as not successful.

    #!/bin/bash
#The following function returns a value of 0 or 1
function if_running(){
    ps -ef | grep -w "$1" | grep -v grep > /dev/null
    if [[ $? == 0 ]]; then
        return 0
    else
        return 1
    fi
}

#Read in name of a running process
read -p "Enter a name of a process: "

#Send REPLY to function
if_running $REPLY

#Check return value and echo appropriately
if [[ $? == 0 ]]; then
   echo "Return value is $?"
   echo "$REPLY is running..."
else
   echo "Return value is $?"
   echo "$REPLY is not running..."
fi

    Examples:

    ~$ ./ps_test.bsh 
Enter a name of a process: ls
Return value is 1
ls is not running...

~$ ./ps_test.bsh 
Enter a name of a process: bash
Return value is 0
bash is running...

    And this answer I wrote a little bit ago does not have return values but still gives output https://askubuntu.com/a/1023493/231142

    #!/bin/bash
function area(){
    circ=$(echo "3.14 * $1^2" | bc)
}

#Read in radius
read -p "Enter a radius: "

#Send REPLY to function
area $REPLY

#Print output
echo "Area of a circle is $circ"

    Example:

    terrance@terrance-ubuntu:~$ ./circ.bsh 
Enter a radius: 6
Area of a circle is 113.04

    Hope this helps!

    • 4