I wrote following bash script. The read command creates variable var.
if $var==5 then break loop.
seq 10 | while read -r var
do
echo "read: $var"
if [[ $var == 5 ]]; then
echo "break loop: $var"
break
fi
done
echo "after loop: $var"
Here is the output
read: 1
read: 2
read: 3
read: 4
read: 5
break loop: 5
after loop:
My question is: why after loop, $var is empty?
The variable isn't loop-local, and everything related to read and loops here are just red herrings. The behavior you're seeing is because the pipe starts a subshell. If you get rid of the pipe and run this code instead:
while read -r var
do
echo "read: $var"
if [[ $var == 5 ]]; then
echo "break loop: $var"
break
fi
done < <(seq 10)
echo "after loop: $var"
Then it will print this instead:
read: 1
read: 2
read: 3
read: 4
read: 5
break loop: 5
after loop: 5
shopt -s lastpipe