How to replace a string in a file?

Hi,

I need to search and replace a string in a file using SKILL.

I want to do this without creating any temp files i.e. open

file in I/O mode and make edits. I was able to this using 

two files using something like the code below. Can somebody

suggest a more efficient way?

Thanks

Aman

infile(xx);

outfile(yy);

when( inPort

    while( gets( nextline inPort)

rexcompile();

rexReplace();

fprintf(yy);

close(yy);