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Linux HowTo's -
Advance Linux HowTo's
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Written by Allen Sanabria
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Sunday, 18 May 2008 16:33 |
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There are a bunch of great regular expressions HowTo's out there..... Now you may be asking why am I creating another??? Well quite simple, I am creating this one because this is not really just a regular expression howto but more a regular expression HowTo with its everyday uses with linux/unix commands. So it will not cover perl/python/ruby/...etc programming languages regular expressions (That will be for another tutorial :) )
To start this off I will give you a basic introduction to regular expressions using the output
of "ls" and piping it "grep" using the -oE options (The o stands for Exact match and the E stands for Extended Regular Expressions). Using "(BRE and ERE) Basic Regular Expressions and Posix Extended Regular Expressions"...
THIS IS NOT A TUTORIAL BUT A HOWTO!! So this means more examples and less explaining..
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Anchors |
What it means |
Example |
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^ |
Start of string |
ls |grep -oE "^C\w+\.jpg"
Chunka.jpg
Chunka1.jpg |
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$ |
End of string |
ls |grep -oE "\w+(\.jpg$)"
Chunka.jpg
Chunka1.jpg
DSCF0732.jpg |
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\b |
Word boundary |
ls |grep -oE "\bChunka\b\.jpg"
Chunka.jpg |
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\< |
Start of word |
ls |grep -oE "\<Ch\w+\.jpg"
Chunka.jpg
Chunka1.jpg |
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\> |
End of word |
ls Scripts/Python/ |grep -oE "\w+\>\.py"
xen_mac_generate.py |
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Character Classes |
What it means |
Example |
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\w |
Word |
ls | grep -oE "\w"
C
C |
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\W |
Non word |
ls |grep -oE "\W"
.
. |
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Quantifiers |
what it means |
example |
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* |
zero or more times |
ls | grep -oE "\w*.jpg"
Chunka.jpg
Chunka1.jpg
DSCF0732.jpg |
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+ |
one or more times |
ls | grep -oE "\w+"
Chunka
Chunka1
DSCF0732 |
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? |
matches either once or zero times |
ls | grep -oE "Chunka1?.jpg"
Chunka.jpg
Chunka1.jpg |
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{2} |
Exactly 2 times |
ls | grep -oE "(^C{2}h\w+.jpg)"
CChunka.jpg |
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{1,} |
1 or more times |
ls | grep -oE "(^C{1,}h\w+.jpg)"
CChunka.jpg
CCChunka.jpg
Chunka.jpg
Chunka1.jpg
Chunka11.jpg |
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{1,2} |
1 through 2 times |
ls | grep -oE "(^C{1,2}h\w+.jpg)"
CChunka.jpg
Chunka.jpg
Chunka1.jpg
Chunka11.jpg |
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Special Characters |
What it means |
Example |
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\n |
New line |
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\r |
Carriage return |
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\t |
Tab |
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\v
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Vertical tab |
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\f |
Form feed |
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Last Updated ( Saturday, 24 May 2008 18:58 )
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