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Full Discussion: grep regular expression
Top Forums Shell Programming and Scripting grep regular expression Post 302316947 by durden_tyler on Sunday 17th of May 2009 11:44:25 AM
Old 05-17-2009
Quote:
Originally Posted by research3
...The command filter contains only lines which start with "aa"!
Nope, the "grep" regex matches all the lines in <file> that have one or more a's and nothing other than a's.

Code:
$
$ cat -n input.txt
     1  a
     2  aa
     3  aaa
     4  aba
     5  abb
     6
     7  b
     8  A
     9  AA
$
$ grep -n "^aa*$" input.txt
1:a
2:aa
3:aaa
$
$

tyler_durden
 

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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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