Syntax for awk

awk <options> 'Program' Input-File1 Input-File2 ...
awk -f PROGRAM-FILE <options> Input-File1 Input-File2 ...

If no Input-File is specified then `awk’ applies the Program to “standard input”, (piped output of some other command or the terminal. Typed input will continue until end-of-file (typing `Control-d’)

Example for search and replace

awk  ‘{ gsub( /search_string/ , replacestring , $0 ); print }’ file

If you want to write the output to a file, then simple redirect the output as shown below:

awk  ‘{ gsub( /search_string/ , replacestring , $0 ); print > output_file }’ file

Hope, it helps!