This example program interprets the arguments as file names and replaces the string "dog" by "cat" in the corresponding files

 $ include "seed7_05.s7i";       # Standard Seed7 library
   include "getf.s7i";           # Import the getf and putf functions

 const proc: main is func
   local
     var string: file_name is "";
   begin
     for file_name range argv(PROGRAM) do
       putf(file_name, replace(getf(file_name), "dog", "cat"));
     end for;
   end func;

The 'getf' function reads the complete file with the name 'file_name' into a string and returns it. Since strings can have any length and can contain any data (even zero bytes) this is possible. The 'replace' function replaces "dog" by "cat" and after that the 'putf' function writes the string back to the file with the name 'file_name'.