UNIX for Dummies Questions & Answers

Hi,

i have a tab dilimeted file.The records are :header is having column names.I am facing the following issue :
I want to convert the spaces only for header file into "_" in the unix shell but the problem is that if i use sed command all the blank spaces are getting replaced by "_".
For example:head -1 samlpe.txt
EMP ID EMP NAME EMP DETAIL EMP CONTACT EMP LOCATION
Want to Convert into
EMP_ID EMP_NAME EMP_DETAIL EMP_CONTACT EMP_LOCATION

Can anybody help regarding this?
Thanks in Advance!

Code:

echo $header | sed "s/EMP /EMP_/g"

or

Code:

head -1 sample.txt | sed "s/EMP /EMP_/g"

using perl:

Code:

perl -pi -e 's/EMP /EMP_/g  if ($. == 1);' filename

Can you explain in detail how perl works and what is the benefit of perl when compared to sed and awk commands.......