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I'm wondering what's the difference between using * and .* in a regex string.

I guess, * stands for "0 to n characters" but I don't see what .* stands for.

For example, what is the difference between: "2013*11*27" and "2013.*11.*27"? If I take a look to 

find . -name [pattern]

As pattern I tried : "2013.*11.*25" and it didn't find "2013-11-25" however, with "2013*11*25", it finds it.

Why ? In unix, 0 or n occurences of wildcards is : *, in regex .* so why doesn't it work ?

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2 Answers 2

up vote 2 down vote accepted

* stands for 0 or more arbitrary characters in shell wildcard matches.

* stands for 0 or more occurrences of the preceding expression in regex matches.

. stands for single arbitrary character in regex matches.

Thus, * in shell wildcard match is equivalent to .* in regex match.

"2013*11*27" in regex match will match "2013333111111111127" but not "2013-11-27" but if you use it to find files, e.g. as argument to ls, letting the shell handle it as "shell wildcard match" (and not regex) it will capture "2013-11-27" just fine.

*(in your case, the expression is a single character matching exactly that character, 3 and 1 respectively.)

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up vote 2 down vote

First, you need to separate regexp from unix shell pattern.
In ksh command expect special option, you will use unix pattern.
if you use for example grep -R you will use regexp.

The * in regex synthax mean 0 or n occurences.
The * in unix pattern mean any string and depending on the settings with or without line jump.
If you use regexp .* means any char except jump line 0 or n time
and using * in a regex will match the previous char 0 or n time.

.* in regexp is equivalent of unix pattenr *

find -name use unix pattern so using .* in a pattern stand for finding .ANY_STRING_OR_NO_STRING no any sring.
tu use regexp use
find -regex

Regard

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I'm still missing something. If I do : find . -name [pattern] As pattern I tried : "2013.*11.*25" and it didn't find "2013-11-25" however, with "2013*11*25", it finds it. If I take a look to what you wrote above, in regexp, I should used .* to say "0 or n occurences of wild card" –  user1058398 Nov 27 '13 at 10:18
    
``find -name` use pattern and not regexp so .* in your search stand for 2013.anystring11.anystring225. You must use find -regexp to use regexp instaed pattern –  Kiwy Nov 27 '13 at 10:22
    
Ok Thank you. However, by default, grep use regexp ? –  user1058398 Nov 27 '13 at 10:31
    
no to use regexp in grep you must provide the argumen -R. You should consider the use of man grep or any man ;) –  Kiwy Nov 27 '13 at 10:35
    
Yeah, but actually I thought that in man pages, pattern was used for regexp. But ok thank you. –  user1058398 Nov 27 '13 at 12:34

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