While the loop checks if the file exists in bash

Question

I am working on a shell script that makes certain changes to the txt file only if it exists, but this test loop does not work, I wonder why? Thank!

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

Answer 1

When you say "does not work," how do you know that it does not work?

You can try to find out if the file exists by adding:

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

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

Answer 2

If you 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 caused by sleep while still checking every 2 seconds. You can add more events if you expect them to be needed.

Answer 3

I had the same problem, set it! out of brackets;

 while ! [ -f /tmp/list.txt ]; do echo "#" sleep 1 done 

Also, if you add an echo inside the loop, it will tell you whether you get into the loop or not.

Answer 4

I ran into a similar problem and it brought me here, so I just wanted to leave my solution for those who are experiencing the same.

I found that if I ran cat /tmp/list.txt , the file would be empty, although I was sure that the contents were immediately placed in the file. It turns out if I put sleep 1; just before cat /tmp/list.txt , it worked as expected. There should have been a delay between the time the file was created and the time it was written, or something in that direction.

My last code is:

 while [ ! -f /tmp/list.txt ]; do sleep 1; done; sleep 1; cat /tmp/list.txt; 

Hope this helps save someone a disappointing half hour!

Answer 5

do it like that

 while true do [ -f /tmp/list.txt ] && break sleep 2 done ls -l /tmp/list.txt