Force flushing of output to a file while bash script is still running

user_154510 0
Viewed 137476

I have a small script, which is called daily by crontab using the following command:

/homedir/MyScript &> some_log.log

The problem with this method is that some_log.log is only created after MyScript finishes. I would like to flush the output of the program into the file while it's running so I could do things like 

tail -f some_log.log

and keep track of the progress, etc.

flush file bash
13 Answers

Would this help?

tail -f access.log | stdbuf -oL cut -d ' ' -f1 | uniq

This will immediately display unique entries from access.log using the stdbuf utility.

user_1459890

Thanks @user3258569, script is maybe the only thing that works in busybox!

The shell was freezing for me after it, though. Looking for the cause, I found these big red warnings "don't use in a non-interactive shells" in script manual page:

script is primarily designed for interactive terminal sessions. When stdin is not a terminal (for example: echo foo | script), then the session can hang, because the interactive shell within the script session misses EOF and script has no clue when to close the session. See the NOTES section for more information.

True. script -c "make_hay" -f /dev/null | grep "needle" was freezing the shell for me.

Countrary to the warning, I thought that echo "make_hay" | script WILL pass a EOF, so I tried

echo "make_hay; exit" | script -f /dev/null | grep 'needle'

and it worked!

Note the warnings in the man page. This may not work for you.

user_2077910

alternative to stdbuf is awk '{print} END {fflush()}' I wish there were a bash builtin to do this. Normally it shouldn't be necessary, but with older versions there might be bash synchronization bugs on file descriptors.

user_33039580
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