Question

I have the following Bash script. How can I make it pause on keypress or pause after a number of loops, but if I don’t press any key it should loop?

for i in `cat files` 
do
    echo $i
done

Answer 1

I think I initially misread your question. You can suspend the active process at any time by pressing Ctrl+Z, and resume it with the fg builtin.

In order to make the script pause after a number of iterations have been performed, you can use a counter variable and the modulo operator %:

i=1
for f in `cat files`; do
    echo $f
    if (( i % 10 == 0 )); then  # pause every 10 iterations
        read
    fi
    let "i++"
done

---

My original answer was:

You can use the read builtin to have the shell wait until the user presses the RETURN key (or the EOF key, Ctrl+D):

for i in `cat files`
do
    echo $i
    read
done

You can use the -t option of read in order have it time out and continue execution:

for i in `cat files`
do
    echo $i
    read -t 1
done

The above will resume execution after 1 second if the user doesn’t press the RETURN key.