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Full Discussion: grep sed and a loop
Top Forums UNIX for Dummies Questions & Answers grep sed and a loop Post 302521308 by agama on Tuesday 10th of May 2011 10:32:32 PM
Old 05-10-2011
It sounds like you're working with a daemon's log file and if so you'll need to be careful. If you overlay the open log file, you'll stop seeing updates to the file as you will have unlinked the open file from the directory and replaced it with a static file that you marked up with hash (#) signs.

I think you have two choices:

1) use tail -f to read the log file and pipe the output through grep or awk to do what you need. This is probably easiest.

2) if your log file has timestamps then you can run your search periodically. With each run save the last time stamp in the log file, tuck it away in a /tmp file or something, and only process messages in the log that have a timestamp greater than the last one saved.

Small sample of using tail:
Code:
tail -f /var/log/foo | grep "Can not load CRL"  >capture-file

 

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LEARN ABOUT MINIX

grep

GREP(1) 						      General Commands Manual							   GREP(1)

NAME

       grep - search a file for lines containing a given pattern

SYNOPSIS

       grep [-elnsv] pattern [file] ...

OPTIONS

       -e     -e pattern is the same as pattern

       -c     Print a count of lines matched

       -i     Ignore case

       -l     Print file names, no lines

       -n     Print line numbers

       -s     Status only, no printed output

       -v     Select lines that do not match

EXAMPLES

       grep mouse file	   # Find lines in file containing mouse

       grep [0-9] file	   # Print lines containing a digit

DESCRIPTION

       Grep  searches  one  or	more  files (by default, stdin) and selects out all the lines that match the pattern.  All the regular expressions
       accepted by ed and mined are allowed.  In addition, + can be used instead of * to mean 1 or more occurrences, ? can be used to mean 0 or  1
       occurrences,  and  |  can  be used between two regular expressions to mean either one of them.  Parentheses can be used for grouping.  If a
       match is found, exit status 0 is returned.  If no match is found, exit status 1 is returned.  If an error is detected,  exit  status  2	is
       returned.

SEE ALSO

       cgrep(1), fgrep(1), sed(1), awk(9).

																	   GREP(1)
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