Exiting a shell script from inside a while loop

Question

I'm writing a simple shell script that should exit with 0 if an input string is found in a file, and exit with 1 if it isn't

INPSTR=$1

cat ~/file.txt | while read line
do
    if [[ $line == *$INPSTR* ]]; then
        exit 0
    fi
done

#string not found
exit 1

What's actually happening is that when the string is found, the loop exits, and the shell then goes to "exit 1". What's the correct way to exit from the shell script entirely while in a loop?

Answer 1

You need to avoid creating sub-shell in your script by avoiding the pipe and un-necessary cat:

INPSTR="$1"

while read -r line
do
    if [[ $line == *"$INPSTR"* ]]; then
        exit 0
    fi
done < ~/file.txt

#string not found
exit 1

Otherwise exit 0 is only exiting from the sub-shell created by pipe and later when loop ends then exit 1 is used from parent shell.

Answer 2

you can catch return code of subshell using $? like this

INPSTR=$1
cat ~/file.txt | while read line
do
if [[ $line == *$INPSTR* ]]; then
    exit 0
fi
done
if [[ $? -eq 0 ]]; then
    exit 0
else
#string not found
    exit 1
fi