I'm re-phrasing the question because it was highly confusing and was badly phrased... )-:

I have a docker container and I'm reading logs from it like this:

docker exec -it my-container sh -c "export TERM=xterm && ls -t /logs/my-log.* | xargs zless -R"

now, I want to use 'grep' on the output and I am facing a problem because this one is working:

docker exec -it my-container sh -c "export TERM=xterm && ls -t /logs/my-log.* | xargs zless -R | grep sometext"

while this one is not working:

docker exec -it my-container sh -c "export TERM=xterm && ls -t /logs/my-log.* | xargs zless -R" | grep sometext

(note that the 1st working command includes the grep within the command I send and in the 2nd one I run grep on the output)

it is important to me because I am running the command in a script and I want to allow running grep on this script's output.

  • What do you mean by multiple piped ones? – countermode Feb 7 '17 at 15:05
  • Something like that: scrpt my-container my-file | grep sometext | head -n 1 – Hovav Feb 7 '17 at 18:16
  • you could just mount external volumes onto your container for this logging then perform a simpler grep directly from the host to avoid having to docker exec onto the container ... I realize this may not always be possible or advisable yet its an option – Scott Stensland Oct 18 '18 at 11:05

the script is running 'exec -it', 't' stands for tty

zless is "thinking" it has a tty in front of it without the additional pipe...

removing the 't' solved the problem (although it is now acts like a zcat and not zless but since piping is working I can simply pipe it into less...)

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I don't really see the point of the pipeline. zless is an interactive program, and the output of ls is to be looked at, not parsed.


... sh -c 'zgrep PATTERN /logs/my-log.*'

or, if there are too many files,

... sh -c 'for pathname in /logs/my-log.*; do zgrep PATTERN "$pathname"; done'

or, more efficiently,

... sh -c 'find /logs/ -maxdepth 1 -type f -name "my-log.*" -exec zgrep PATTERN {} +'
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