Do a tail -F until matching a pattern

shell sed awk tcl tail
Sam Alba picture Sam Alba · Feb 17, 2011 · Viewed 20.3k times · Source

I want to do a tail -F on a file until matching a pattern. I found a way using awk, but IMHO my command is not really clean. The problem is that I need to do it in only one line, because of some limitations.

tail -n +0 -F /tmp/foo | \
awk -W interactive '{if ($1 == "EOF") exit; print} END {system("echo EOF >> /tmp/foo")}'

The tail will block until EOF appears in the file. It works pretty well. The END block is mandatory because awk's "exit" does not exit right away. It makes awk to eval the END block before quitting. The END block hangs on a read call (because of tail), so the last thing I need to do, is to write another line in the file to force tail to exit.

Does someone know a better way to do that?

Answer

Greg Barrett picture Greg Barrett · Feb 25, 2011

Use tail's --pid option and tail will stop when the shell dies. No need to add extra to the tailed file.

sh -c 'tail -n +0 --pid=$$ -f /tmp/foo | { sed "/EOF/ q" && kill $$ ;}'

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