What is meaning of given line?

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12-12-2014

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What is meaning of given line?

Hello Guys,

I was study some links, where I was unable to understand below line, please enhance me these code.

Quote:

sed 's/\([a-z]*\) \1/\1/'

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Code:

sed 's/\([a-z]*\) \1/\1/'

is a basic (obsolete) regular expression, which replaces the first occurrence of zero or more lower case chars (lets call it PAT1) followed by a space followed by PAT1 again. In fact, it replaces the first space in every single line, as it matches PAT1 with the NULL (empty) string.

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Please give me example of above basic regular expression so that I can understand well.

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Hello Aditya,

Here are some examples for basic sed operations. Let's say we have an input file as follows.

Code:

cat check_pipie
1|John|32|US|
2|Matt|35|UK
3|Rex|36|EU|

Then some of the examples are as follows for sed with a little regular expresssions.

Code:

1- sed 's/|/\"/g' check_pipie
#### To subtitute string | with string "
 
2-  sed 's/^[^.]\{2\}//g' check_pipie
##### To remove 1st 2 characters in each line.
 
3- sed 's/[[:alpha:]]//g' check_pipie
##### To remove all alphabetic characters in file.
 
4- sed 's/\(..\)$//g' check_pipie
#### To remove last 2 characters in file.

Also following links may be helpful for you to understand sed more with some examples and details.

https://www.gnu.org/software/sed/man...pressions.html
Unix - Regular Expressions with SED
GNU Regular Expression Extensions - Gnulib Regex Module

Thanks,
R. Singh

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