I am running a process in linux which logs the status and others info in a log file /home/path/Detail_File.log in text format. the file is being continuously written using a background process. I can display the file contents using tail -f /home/path/Detail_File.log.

I want to check the file for a key word keyword (say). How do I continuously check if the key word is found, and if found get that line in a variable.

I am not sure what should I search on internet so posting this question directly without the primary research. Any suggestion would be appreciated.

EDIT 1: Adding screenshot of the while loop suggestion by @jhnc

The echo "Time elapsed: $curr_time ..." is executed and then its silent

CodePudding user response：

If you are using GNU utilities, grep has a --line-buffered option:

tail -n  1 -f /home/path/Detail_File.log |\
grep --line-buffered -F keyword |\
while read matchedline; do
    dosomething "$matchedline"
done

This is a pipeline: cmd1 | cmd1 | cmd3

Backslash (\) at end of line allows using linebreak for readability.

• tail output is fed into grep.
• grep output is fed into the while loop.
• read gets its input from grep, not from the user.

Usually, grep output is buffered - the output only becomes available once the pipe buffer is full. The --line-buffered option causes the pipe buffer to be flushed after every line. For example, consider difference between output of:

while sleep 1; do date; done |\
grep --line-buffered . |\
while read line; do echo "$(date) :: $line"; done |\
head

versus (may take a few minutes before you see anything):

while sleep 1; do date; done |\
grep . |\
while read line; do echo "$(date) :: $line"; done |\
head