command line - weird shell script error: invalid option return: usage: return [n]

This programme checks if a certain book title exist by matching user input of book title and book author.

function removebook_option()
{
    echo -n "Title : "
    read title_input2
    echo -n "Author: "
    read author_input2
    checkexist $title_input2 $author_input2
    error=$?
    echo "$error"
    if [ $error != -1 ];then
        #removebook
            echo "New book title $title_input removed successfully"
        else
        echo "Book does not exist"
    fi
}
function checkexist()
{
   counter=0
   for x in ${title[@]}
   do
    for y in ${author[@]}
    do
        if [  $x == $1 ] && [ $y == $2 ];
        then
            error=$counter
                return "$error"
        fi
    done
    counter=$((counter+1))
   done
   error=-1
   return "$error"
}
title=(foo1 foo2)
author=(bar1 bar2)
removebook_option

I am getting a very weird error , where function checkexist() returns 2 instead of -1 when there isnt a match which happens when returning value error=-1

line 43: return: -1: invalid option return: usage: return [n]

EDIT : For reasons unknown , i can only return values from 0-255 , does anyone know how to return negative values??

You can try to input incorrect data to see the weird error

I need help resolving this issue thanks!!!!

You're getting this error:

line 43: return: -1: invalid option return: usage: return [n]

This is because the -1 is interpreted as an option. Use this, -- means 'end of options':

return -- -1

which returns with 255.

---

Working solution:

#!/bin/bash
function removebook_option()
{
    echo -n "Title : "
    read title_input2
    echo -n "Author: "
    read author_input2
    error="$(checkexist "$title_input2" "$author_input2")" # <--
    echo "$error"
    if [[ "$error" != NOT_FOUND ]]; then # <--
        #removebook
        echo "New book title $title_input removed successfully"
    else
        echo "Book does not exist"
    fi
}
function checkexist()
{
   counter=0
   for x in "${title[@]}" # <--
   do
        for y in "${author[@]}" # <--
        do
            if [[  $x == $1 ]] && [[ $y == $2 ]]; # <--
            then
                error=$counter
                echo "$error" # <--
                return
            fi
        done
        ((counter++)) # <--
   done
   error=NOT_FOUND # <--
   echo "$error"
   return
}
title=(foo1 foo2)
author=(bar1 bar2)
removebook_option

Edits marked with  # <--

This works by instead of returning an integer value, it echoes it (writes to screen). Usually, this would print to the terminal however the $( ... ) syntax captures the printed output, and assigns it to error in removebook_option(). This allows 'returning' any string, I've made it return a sentinel value of NOT_FOUND if not found.

Notes:

• Array expansion should be wrapped with double quotes: "${author[@]}" and "${title[@]}"


• Use [[ ... ]] instead of [ ... ].