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Monitor a file with tail with timestamps added

Terminal - Monitor a file with tail with timestamps added
tail -f file | while read line; do echo -n $(date -u -Ins); echo -e "\t$line"; done
2010-11-19 10:01:57
User: hfs
Functions: date echo file read tail
6
Monitor a file with tail with timestamps added

This is useful when watching a log file that does not contain timestamps itself.

If the file already has content when starting the command, the first lines will have the "wrong" timestamp when the command was started and not when the lines were originally written.

Alternatives

There are 2 alternatives - vote for the best!

Terminal - Alternatives
tail -f file | awk '{now=strftime("%F %T%z\t");sub(/^/, now);print}'
tail -f file | while read line; do printf "$(date -u '+%F %T%z')\t$line\n"; done
2010-11-24 05:50:12
User: derekschrock
Functions: file printf read tail
Tags: tail date
4

Should be a bit more portable since echo -e/n and date's -Ins are not.

tail -f file |xargs -IX printf "$(date -u)\t%s\n" X

Know a better way?

If you can do better, submit your command here.

What others think

Where did you find -I switch? I don't see it in man date ...

Comment by depesz 301 weeks and 1 day ago

Mmh, I don't remember. It's not listed in my man page, either. It seems to be the short form of '--rfc-3339='.

Comment by hfs 301 weeks ago

Could be written with a single echo and without the 'line' variable

tail -f file | while read; do echo -e "$(date -u -Ins)\t$REPLY"; done
Comment by frans 300 weeks and 5 days ago

-I is for ISO8601

http://en.wikipedia.org/wiki/ISO_8601

But I don't know what the ns TIMESPEC would be..

Comment by derekschrock 300 weeks and 3 days ago

Your point of view

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