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Full Discussion: The asterisk in regex
Top Forums UNIX for Dummies Questions & Answers The asterisk in regex Post 302649009 by sudon't on Wednesday 30th of May 2012 04:23:27 PM
Old 05-30-2012
The asterisk in regex

I know through (my very limited) experience that you can't use the asterisk alone in a regex, but I still don't quite understand why. After all, it should match 'any or no characters'. To my mind, '*grep' should match:

grep
egrep
fgrep

While '.*grep' should match

egrep
fgrep

...but not 'grep' because it seems like we are insisting upon a character in front of 'grep' with that dot. Yet that is clearly not the case. Can someone explain why this is so?
(Hope my use of 'grep' as the search term doesn't cause any confusion)
 
ZGREP(1)						      General Commands Manual							  ZGREP(1)

NAME
zgrep - search possibly compressed files for a regular expression SYNOPSIS
zgrep [ grep_options ] [ -e ] pattern filename... DESCRIPTION
Zgrep is used to invoke the grep on compress'ed or gzip'ed files. All options specified are passed directly to grep. If no file is speci- fied, then the standard input is decompressed if necessary and fed to grep. Otherwise the given files are uncompressed if necessary and fed to grep. If zgrep is invoked as zegrep or zfgrep then egrep or fgrep is used instead of grep. If the GREP environment variable is set, zgrep uses it as the grep program to be invoked. For example: for sh: GREP=fgrep zgrep string files for csh: (setenv GREP fgrep; zgrep string files) AUTHOR
Charles Levert (charles@comm.polymtl.ca) SEE ALSO
grep(1), egrep(1), fgrep(1), zdiff(1), zmore(1), znew(1), zforce(1), gzip(1), gzexe(1) ZGREP(1)
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