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Top Forums UNIX for Dummies Questions & Answers Please explain this grep command Post 302797511 by hanson44 on Monday 22nd of April 2013 05:15:37 PM
Old 04-22-2013
Quote:
why do we even need the A option
grep -A N prints N lines of "after-context". That means it prints the matching line, and then the next N lines. So grep regexp -A 999999 prints the matching line and the next 999999 lines. The reason they chose six nines is they figured that was such as big number that it would print the rest of the log file, is my guess. 999999 is a very big number, in terms of number of lines for a log file. So the overall intention is to count the number of lines with 'Option=\[Yes\]' that occur AFTER the line with regexp.
 

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GREP(1) 						      General Commands Manual							   GREP(1)

NAME
grep - search a file for a pattern SYNOPSIS
grep [ option ... ] pattern [ file ... ] DESCRIPTION
Grep searches the input files (standard input default) for lines (with newlines excluded) that match the pattern, a regular expression as defined in regexp(6). Normally, each line matching the pattern is `selected', and each selected line is copied to the standard output. The options are -c Print only a count of matching lines. -h Do not print file name tags (headers) with output lines. -i Ignore alphabetic case distinctions. The implementation folds into lower case all letters in the pattern and input before interpre- tation. Matched lines are printed in their original form. -l (ell) Print the names of files with selected lines; don't print the lines. -L Print the names of files with no selected lines; the converse of -l. -n Mark each printed line with its line number counted in its file. -s Produce no output, but return status. -v Reverse: print lines that do not match the pattern. Output lines are tagged by file name when there is more than one input file. (To force this tagging, include /dev/null as a file name argument.) Care should be taken when using the shell metacharacters $*[^|()= and newline in pattern; it is safest to enclose the entire expression in single quotes '...'. SOURCE
/sys/src/cmd/grep.c SEE ALSO
ed(1), awk(1), sed(1), sam(1), regexp(6) DIAGNOSTICS
Exit status is null if any lines are selected, or non-null when no lines are selected or an error occurs. GREP(1)
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