in reply to how to modify the text in file
in thread ho w to replace a occurence of string by other string

now what i had tried actually replaces the xxx1.data , i do not want to delete the string only add new text before it.

What have you tried? Show us some code...

If you tried 

s[\w\w\w1\.data][$testname/]g

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you might consider 
s[(\w\w\w1\.data)][$testname/$1]g

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instead.

The $1 stands for the text enclosed in the first set of round brackets in the pattern.

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Re^2: how to modify the text in file
by sachin_chat (Initiate) on Jan 19, 2005 at 07:19 UTC
    i was using something like perl -npi.bak -e "s:(\w\d+\.data):testname/$1:g" file1.txt . it actually repleces the text and do not do what i wanted
[reply]
      1. First, you need to replace "\w\d+" with "\w+\d+". Otherwise, your regex is only going to match "x1.data" instead of "xxx1.data".
      2. Second, I assume you're using bash, sh, or a similar shell on a Unix box. When passing arguments using double-quotation marks, you need to escape any backslashes, dollar signs, and certain other characters. I recommend using single-quotation marks instead since most characters don't have to be escaped inside them.

      Suggestion:

      perl -npi.bak -e 's:(\w+\d+\.data):testname/$1:g' file1.txt
[reply]
      Aha ! 
      perl -npi.bak -e "s:(\w\d+\.data):testname/$1:g" file1.txt

      [download]
      That is a shell quoting problem. Your $1 gets replaced by an (empty) environment variable before Perl sees it. Use single quotes: 
      perl -npi.bak -e 's:(\w\d+\.data):testname/$1:g' file1.txt

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