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

User · Answer

Like  zane-hooper  I ve had a similar problem on NFS  On parallel   distributed filesystems the lag between you creating a file on one machine and the other machine  seeing  it can be very large  so I could wait up to a full minute after the creation of the file before the while loop exits  and there also is an aftereffect of it  seeing  an already deleted file     This creates the illusion that the script  doesn t work   while in fact it is the filesystem that is dropping the ball   This took me a while to figure out  hope it saves somebody some time   PS This also causes an annoying number of  Stale file handler  errors

User · Answer

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

User · Answer

do it like this  while true do     -f  tmp list txt    amp  amp  break   sleep 2 done ls -l  tmp list txt

User · Answer

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

User · Answer

I had the same problem  put the   outside the brackets   while     -f  tmp list txt    do     echo         sleep 1 done   Also  if you add an echo inside the loop it will tell you if you are getting into the loop or not

User · Answer

I ran into a similar issue and it lead me here so I just wanted to leave my solution for anyone who experiences the same   I found that if I ran cat  tmp list txt the file would be empty  even though I was certain that there were contents being placed immediately in the file  Turns out if I put a sleep 1  just before the cat  tmp list txt it worked as expected  There must have been a delay between the time the file was created and the time it was written  or something along those lines   My final code   while     -f  tmp list txt    do     sleep 1  done  sleep 1  cat  tmp list txt    Hope this helps save someone a frustrating half hour

User · Answer

works with bash and sh both   touch  tmp testfile sleep 10  amp  amp  rm  tmp testfile  amp  until     -f  tmp testfile   do    echo  testfile still exist        sleep 1 done echo  now testfile is deleted

User · Answer

Here is a version with a timeout so that after an amount of time the loop ends with an error     After 60 seconds the loop will exit timeout 60  while     -f  tmp list txt    do     When the timeout is equal to zero  show an error and leave the loop    if     timeout     0    then     echo  ERROR  Timeout while waiting for the file  tmp list txt       exit 1   fi    sleep 1      Decrease the timeout of one     timeout--   done

[bash] While loop to test if a file exists in bash

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