Question

I have a shell script where I pass a txt file to the script as follows:

./run.sh < list.txt

Within the script, I am doing a “while read LIST do ... end“

It all works well, and the script executes using the list.

However, now I want to have a second while read LIST do ... end in the same shell script. I want it to read again from the original list I’m passing it on execution, but it doesn’t work. It reads the list.txt file for the first loop, but not the second.

What do I do to make the script read list.txt each time I’m asking for it?

Answer 1

You can’t read stdin twice. Try passing list.txt on the command-line rather than redirecting it.

./run.sh list.txt

Then in your script:

while read LINE; do
    ...
done < "$1"

while read LINE; do
    ...
done < "$1"

Alternatively, save the contents of stdin off the first time you read through it. For instance:

# First loop, save stdin in an array.
LINES=()

while read LINE; do
    LINES+=("$LINE")
    ...
done

# Second loop, iterate over the array.
for LINE in "${LINES[@]}"; do
    ...
done