Why is this Bash script not changing the string's value?

Question

I can't understand why userType is not changing.

I know for certain it's successfully reaching determineType, but it isn't changing the value to "bbb" when I try to print out userType later.

userType="aaa"

function determineType {
    userType="bbb"
}

function checkUser {
    cat users.csv | \
    while read userLine; do
        if [[ $userLine =~ .*$user.* ]]
            then
            determineType
            echo "1"
        fi
    done
    echo "0"
}

It would be nice if you could rephrase the question in a way that would make it less localized and more useful for other people. — Lev Levitsky, Nov 26 '12 at 11:00
Your `while` loop is a completely new subshell http://stackoverflow.com/questions/124167/bash-variable-scope — soulseekah, Nov 26 '12 at 11:01
Have a look at "global vs. local" bash variables. http://www.thegeekstuff.com/2010/05/bash-variables/ — cb0, Nov 26 '12 at 13:42

score 2 · Answer 1 · answered Nov 26 '12 at 13:35

You are using a pipe, which launch the while .. do in a subshell. Changing the value of a variable in a subshell won't affect the original variable

You should replace the:

function checkUser {
    cat users.csv | \
    while read userLine; do
        if [[ $userLine =~ .*$user.* ]]
            then
            determineType
            echo "1"
        fi
    done
    echo "0"
}

with

function checkUser {
    while read userLine; do
        if [[ $userLine =~ .*$user.* ]]
            then
            determineType
            echo "1"
        fi
    done < users.csv
    echo "0"
}

(This also get rid of a Useless Use Of Cat)

score 2 · Accepted Answer · answered Nov 26 '12 at 13:40

As soulseekah said in a comment, your while loop is executed in a subshell. Instead, do (and, as a benefit, you get rid of the useless use of cat):

userType="aaa"

determineType() {
    userType="bbb"
}

checkUser() {
    while read userLine; do
        if [[ $userLine = *$user* ]]; then
            determineType
            return 1
        fi
    done < users.csv
    return 0
}

Note. I also changed a few things:

got rid of the useless regexp since the same can be achieved with globbing,
used more common ways of defining functions in bash,
used return instead of echo for returning values: you'd run into the same problem again with an echo: you'd probably use your function checkUser in another subshell to obtain the value returned by the echo.

Why is this Bash script not changing the string's value?

2 Answers2