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Full Discussion: Understanding pattern matching used in a grep command
Top Forums Shell Programming and Scripting Understanding pattern matching used in a grep command Post 302605190 by agama on Tuesday 6th of March 2012 09:36:31 PM
Old 03-06-2012
Code:
echo "--help" | grep -iE '--help'

grep sees '--help' as an option.

If I were putting this into a script I'd code it this way:

Code:
echo "--help" | grep -iE --    '--help'

Extra spaces aren't needed, just set the pattern off a bit. The first pair of dashes end greps search for flags, and thus it treats --help as the pattern.

---------- Post updated at 21:36 ---------- Previous update was at 21:34 ----------

Quote:
Correct me if I am wrong on the following:

In the regular expression [-]-help, the - inside the square brackets matches a character set which contains a single character ( - in this case) and the literal string "-help".
You are correct.
Last edited by agama; 03-06-2012 at 10:37 PM.. Reason: removed extra jibberish
 

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LEARN ABOUT NETBSD

zgrep

ZGREP(1)						    BSD General Commands Manual 						  ZGREP(1)

NAME

     zgrep, zegrep, zfgrep -- print lines matching a pattern in gzip-compressed files

SYNOPSIS

     zgrep [grep-flags] [--] pattern [files ...]

     zegrep [grep-flags] [--] pattern [file ...]

     zfgrep [grep-flags] [--] pattern [file ...]

DESCRIPTION

     zgrep runs grep(1) on files or stdin, if no files argument is given, after decompressing them with zcat(1).

     The grep-flags and pattern arguments are passed on to grep(1).  If an -e flag is found in the grep-flags, zgrep will not look for a pattern
     argument.

     zegrep calls egrep(1), while zfgrep calls fgrep(1).

EXIT STATUS

     In case of missing arguments or missing pattern, 1 will be returned, otherwise 0.

SEE ALSO

     egrep(1), fgrep(1), grep(1), gzip(1), zcat(1)

AUTHORS

     Thomas Klausner <wiz@NetBSD.org>

BSD
								 December 28, 2003							       BSD
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