A quick'n'dirty Python script to make find & replace operations on large text files fast and automated. Creates a duplicate file copy and leaves the original file unchanged.

find_replace.py

#!/usr/bin/python
## Configuration ##
__target_file__ = "example.txt"                                     # Relative path to the target file to process.
__find__ = "found"                                                  # Block of text to find.
__replace__ = "replaced"                                            # Block of text to replace with.
###################
with open(__target_file__) as file_in:                              # Open source file for reading.
    file_out = open(__target_file__+"_replaced", 'w')               # Open destination file for writing.
    for line in file_in:                                            # Loop through source, line by line.
        new_line = line.replace(__find__,__replace__)               # Perform find & replace on current line.
        print >>file_out, new_line                                  # Write new line to destination file.
    print "Done!"
print "End of script! Did it work?"