Python ＆ Perl: Find/Replace Strings in a File

This pages shows a simple example of Python ＆ Perl scripts for find ＆ replace strings in a file.

Python

# -*- coding: utf-8 -*-
# python

import sys

nn = len(sys.argv)

if nn != 5:
     print "Error: number of arguments does not match. Syntax should be: %s searchString replaceString inputFile outputFile" % sys.argv[0]
else:
     searchStr = sys.argv[1]
     replaceStr = sys.argv[2]
     inputFile = open(sys.argv[3])
     outputFile = open(sys.argv[4],'w')

     for thisLine in inputFile:
         outputFile.write(thisLine.replace(searchStr,replaceStr))

     outputFile.close()
     inputFile.close()

Save this code as “find_replace.py” and run it like this:

python find_replace.py findStr replacementStr inputFile outputFile

The “sys.argv” is from the module “sys”. The value of sys.argv[0] is the calling script's name itself.

Note the idiom for ‹var› in ‹file object›. It will loop thru the lines in file.

This code was originally based from Python Cookbook by Alex Martelli, David Ascher, page 121. amazon

http://docs.python.org/lib/module-sys.html

Perl

Here is a similar code in Perl.

# -*- coding: utf-8 -*-
# perl

if (scalar @ARGV != 4) {die "Error: number of arguments does not match. Syntax should be: $0 searchString replaceString inputFile outputFile\n"}

$searchStr=$ARGV[0];
$replaceStr=$ARGV[1];
$inputFile = $ARGV[2];
$outputFile = $ARGV[3];

open(F1, "<$inputFile") or die "Error: $!";
open(F2, ">$outputFile") or die "Error: $!";

while ($line = <F1>) {
     $line =~ s/$searchStr/$replaceStr/g;
     print F2 "$line";
}

close(F1) or die "Error: $!";
close(F2) or die "Error: $!";

For a full-featured script that does find-replace in Perl, see: Perl: Find/Replace on Multiple Files.