This is the same question you asked before at Finding only names in a dir and searching for case issues and cross posted at other forums. Have you attempted to implement any of the suggestions already made by monks? Where is the code that you've already tried and what problem do you have with it?

As always, try reading How do I post a question effectively?

Well he did say, "I have tried various ways to achieve this..."

From what I see, this means, he's tried posting to perlmonks a couple times now, AND other forums. That's "various".

1. Read file "data.txt" line by line. Every line has name of a directory.
2. Find all the *.c files in current directory and run a loop on these files
3. Inside above loop read every line of current (*.c) file and run a regular expression to match "modem" case-insensitively with word boundary.
4. If any of the match (in case of multiple matches) is not equal to (eq) "modem" print the line and file (*.c) name

I hope this helps

At step #3,for every file I open,I need to search for all the contents present in data.txt ,not only modem,basically for every .c I have to check if any of the dir names in data.txt are present,how do I match that ?am already in a for loop opening each and every .c files

Read the contents of "data.txt" in an array and run a loop on the array as step#1. This way you have all the directory names with you in the array, at the step #3. Run step #3 and #4 for all the names in array instead of just "modem"

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Regards
- Samar

Something like (untested, may need tweaking) should do:

$ find `cat data.txt` -name '*.c' -print0 | -xargs -0 grep -i modem
[download]

Prove it