Bash – Returning a value from a bash function

bashshell-script

I have a function which returns 1 if the number is a valid ten digit number:

valNum()
{
    flag=1
    if [[ $1 != [1-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9] ]]; then
        echo "Invalid Number"
        flag=0
    fi
    return $flag
}

It is getting called by:

if [[ $(valNum $num) -eq 1 ]]; then
      #do something
fi

The function is working fine if the number is valid but is showing syntax error if input a invalid number.

Best Answer

@choroba's answer is correct, however this example might be clearer:

valNum $num
valNumResult=$? # '$?' is the return value of the previous command
if [[ $valNumResult -eq 1 ]]
then
  : # do something
fi

This example is a little longer (setting $valNumResult then querying that value), but more-explicitly describes what happens: that valNum() returns a value, and that value can be queried and tested.

P.S. Please do yourself a favor and return 0 for true and non-zero for false. That way you can use the return value to indicate "why we failed" in the failure case.

Related Solutions

BASH return to main function

There is no nice way (I am aware of) to do that but if you are willing to pay the price...

Instead of putting the code in functions you can put it in files you source. If the functions need arguments then you have to prepare them with set:

set -- arg1 arg2 arg3
source ...

Three files:

testscript.sh

#! /bin/bash

startdir="$PWD"

echo mainscript

while true; do
        echo "begin: helper loop"
        source "${startdir}/func_1"
        echo "end: helper loop"
        break
done

echo mainscript

func_1

echo "begin: func_1"
source "${startdir}/func_2"
echo "end: func_1"

func_2

echo "begin: func_2"
echo break from func_2
break 100
echo "end: func_2"

Result:

> ./testscript.sh
mainscript
begin: helper loop
begin: func_1
begin: func_2
break from func_2
mainscript

Bash – Get specific result from function

You could output all the other content directly to screen assuming you don't ever want to do anything with it other than display.

Something similar to this could be done

#!/bin/bash

function get_usr_choices() {
        #put everything you only want sending to screen in this block
        {
                echo these
                echo will
                echo go
                echo to
                echo screen
        }> /dev/tty
        #Everything after the block is sent to stdout which will be picked up by the assignment below
        echo result
}
choices=$(get_usr_choices)

echo "<choices is $choices>"

Running this returns

these
will
go
to
screen
<choices is result>

Best Answer

Related Solutions

BASH return to main function

Bash – Get specific result from function

Related Question