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I am working on a UNIX box, and trying to run an application, which gives some debug logs to the standard output. I have redirected this output to a log file, but now wish to get the lines where the error is being shown.
My problem here is that a simple
cat output.log | grep FAIL
does not help out. As this shows only the lines which have FAIL in them. I want some more information along with this. Like the 2-3 lines above this line with FAIL. Is there any way to do this via a simple shell command? I would like to have a single command line (can have pipes) to do the above.
619
Use readlines() to Read the range of line from the File You can use an index number as a line number to extract a set of lines from it. This is the most straightforward way to read a specific line from a file in Python. We read the entire file using this way and then pick specific lines from it as per our requirement.
Method 1: fileobject.readlines() A file object can be created in Python and then readlines() method can be invoked on this object to read lines into a stream. This method is preferred when a single line or a range of lines from a file needs to be accessed simultaneously.
grep -C 3 FAIL output.log
Note that this also gets rid of the useless use of cat (UUOC).
197
grep -A $NUM
This will print $NUM lines of trailing context after matches.
-B $NUM prints leading context.
man grep is your best friend.
So in your case:
cat log | grep -A 3 -B 3 FAIL
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