substitution in c-shell script

[vikas.m0502]

I have one file :
mem_x mem_x
mem_x mem_x
...
mem_x mem_x

I want to change this to :
mem_1 mem_1
mem_2 mem_2
...
mem_n mem_n

I am trying it with csh script but it keeps giving some error.
Please help.
Thanks in advance.

 

[meir]

This perl one liner will do it
perl -pi -e 's/x/$./g' <file_name>