[LINUX] A story that did not end with exit when turning while with pipe input

I wrote such a program in bash

fruits.txt

apple
banana
orange

#!/bin/bash

cat fruits.txt | while read LINE do
    echo ${LINE}
    if [ $? -ne 0 ] ; then
        echo "error:${LINE}"
        exit 1;
    fi
done

echo "Successful completion!"
done

Commentary

It is a program that cats the contents of fruit.txt and pipes it to a while statement for standard output.

Try to run

For example, if banana echo fails, the expected output is:

apple
error:banana

However, the actual output is as follows. The script did not end after the error, and the subsequent processing continues.

apple
error:banana
orange
Successful completion!

Cause

When piped to a while statement, the while loop is a child process of the original script It will be executed. Therefore, even if you do exit 1, only the child process will end, The main process will continue.

Solution 1_Pick up the return value of the child process

The parent process picks up the return value 1 of the child process and terminates the parent process abnormally.

cat fruits.txt | while read LINE do
    echo ${LINE}
    if [ $? -ne 0 ] ; then
        echo "error:${LINE}"
        exit 1;
    fi
done

if [ $? -ne 0 ] ; then
    exit 1;
fi

Solution 2 Use the _for statement

Specifying the result of cat in the list of for statements will solve the problem. If you do this, you don't need to define a variable to put the result of cat separately, so it's smart.

for FRUIT in `cat fruits.txt`; do
    echo ${FRUIT} 
done