parse maven output in real time using sed - parsing

Question

I am trying to parse my mvn verify output to only show lines with INFO tags. Please note that maven outputs line to stdout in real time and not by batch. I do not think that it is a problem with maven.
At first I tried to do it with grep:
$ mvn verify | grep INFO
but didn't seem to output lines in real time, as I understand grep buffers its lines before outputting, so I have to wait a few seconds between each flush and then I have tens of lines being printed at the same time, not very convenient. Then I thought I would try with sed.
According to this link, the following command:
sed -n '/PATTERN/p' file
// is equivalent to
grep PATTERN file
and according to this link, the -l option should force sed to flush its output buffer after every newline. So now I am using this command:
$ mvn verify | sed -ln -e '/INFO/p'
but I'm still getting the same result as before, I get a ton of output flushed every 30s or so and I don't know what I've done wrong. Can someone point me in the right direction please?

Answer 1

Try this, if your grep supports it:
mvn verify | grep --line-buffered INFO
If you're doing this in a terminal and still seeing buffered results, it would probably be something earlier than grep doing the buffering, but I'm not familiar with mvn. (And, yes, the -l option to sed should have done the same thing, so the problem may be upstream.)

Answer 2

try this line:
mvn verify | while read line; do echo $line|grep INFO; done

Answer 3

I found what was the problem, I was using a script to colorise maven output (see here) and in fact it was that script that was buffering the output down the pipe. I forgot about it as I was using it as an alias, I guess this is a good lesson, I won't alias as easily in the future. Anyway here is the fix, I changed -e to -le in the last line of the sed call:
mvn $# | sed -e "s/\(\[INFO\]\ \-.*\)/${TEXT_BLUE}${BOLD}\1/g" \
-e "s/\(\[INFO\]\ \[.*\)/${RESET_FORMATTING}${BOLD}\1${RESET_FORMATTING}/g" \
-e "s/\(\[INFO\]\ BUILD SUCCESSFUL\)/${BOLD}${TEXT_GREEN}\1${RESET_FORMATTING}/g" \
-e "s/\(\[WARNING\].*\)/${BOLD}${TEXT_YELLOW}\1${RESET_FORMATTING}/g" \
-e "s/\(\[ERROR\].*\)/${BOLD}${TEXT_RED}\1${RESET_FORMATTING}/g" \
-le "s/Tests run: \([^,]*\), Failures: \([^,]*\), Errors: \([^,]*\), Skipped: \([^,]*\)/${BOLD}${TEXT_GREEN}Tests run: \1${RESET_FORMATTING}, Failures: ${BOLD}${TEXT_RED}\2${RESET_FORMATTING}, Errors: ${BOLD}${TEXT_RED}\3${RESET_FORMATTING}, Skipped: ${BOLD}${TEXT_YELLOW}\4${RESET_FORMATTING}/g"
In effect this is telling sed to flush its output at every new line, which is what I wanted. I am sorry I didn't find another workaround that is more generic. I tried playing around with empty (see man page) and script but none of these solutions worked for me.