Perl commandline search and replace

The better option is using perl command line search and replace option. The syntax is the following.

# perl -i.bak -p -e’s/old/new/g’ filename
s/old/new/g

what this does is searches for pattern “old” and replace it pattern “new”.The g option in does the serch n replace globally in the file, otherwise perl searches and replaces only the first instance of the pattern.

Lets explain the options used.

-e option allows you to define Perl code to be executed by the compiler. For example, it’s not necessary to write a “Hello World” program in Perl when you can just type this at the command line.

# perl -e ‘print “Hello World\n”‘

-p option, adds loops around your -e code.It creates code like this:

LINE:
while (<>) {
# your code goes here
} continue {
print or die “-p destination: $!\n”;
}

-i option. Actually, Perl renames the input file and reads from this renamed version while writing to a new file with the original name. If -i is given a string argument, then that string is appended to the name of the original version of the file. For example, to change all occurrences of “PHP” to “Perl” in a data file you could write something like this:


# perl -i -pe ’s/PHP/Perl/g’ file.txt

Perl reads the input file a line at a time, making the substitution, and then writing the results back to a new file that has the same name as the original file — effectively overwriting it. If you’re not so confident of your Perl abilities you might take a backup of the original file, like this:

# perl -i.bak -pe ’s/PHP/Perl/g’ file.txt