Bash reading STDOUT stream in real-time

Question

I have searched for this and expected to find hundreds of solutions yet found none !

I would like to read the STDOUT stream and wait for a specific string to appear,

Answer 1

You can pipe into grep to do the matching and have it exit when it encounters a match. That will also exit the program producing the output.

if mycommand | grep something -q; then
    dosomething
fi

The above will quit if anything matches (-q), but not display the result. If you want to see the output, you can quit on the first match (using -m1):

RESP=$(mycommand | grep something -m1)

Read the man-pages for grep for more information.

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If you don't want to cancel the program producing the output, you could try writing it to file in the background, then tail that file:

mycommand > output &
if tail -f output | grep something -q; then
    dosomething
fi