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What is meaning of given line?

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# 1  
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.
sed 's/\([a-z]*\) \1/\1/'
# 2  
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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# 3  
Please give me example of above basic regular expression so that I can understand well.
# 4  
Hello Aditya,

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

Then some of the examples are as follows for sed with a little regular expresssions.
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.
Unix - Regular Expressions with SED
GNU Regular Expression Extensions - Gnulib Regex Module

R. Singh
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