While loop to test if a file exists in bash

Question

I'm working on a shell script that does certain changes on a txt file only if it does exist, however this test loop doesn't work, I wonder why? Thank you!

while [ ! -f /tmp/list.txt ] ; do       sleep 2 done 

Answer 1

When you say "doesn't work", how do you know it doesn't work?

You might try to figure out if the file actually exists by adding:

while [ ! -f /tmp/list.txt ] do   sleep 2 # or less like 0.2 done ls -l /tmp/list.txt 

You might also make sure that you're using a Bash (or related) shell by typing 'echo $SHELL'. I think that CSH and TCSH use a slightly different semantic for this loop.

Answer 2

If you are on linux and have inotify-tools installed, you can do this:

file=/tmp/list.txt while [ ! -f "$file" ] do     inotifywait -qqt 2 -e create -e moved_to "$(dirname $file)" done 

This reduces the delay introduced by sleep while still polling every "x" seconds. You can add more events if you anticipate that they are needed.