Revision as of 06:25, 3 May 2013

Perl Regex

How to search and replace a word or phrase

• All matches

 perl -pi -e 's/old string/new string/g' /path/to/the/file
 

This command line replaces all the instances of old string with new string that are found in `/path/to/the/file`.  To replace only the first instance, remove the g at the end of the command.

• Conditional match

 perl -pi -e 's/old string/new string/ if m/my unique string/' /path/to/the/file
 

This command line search only for the lines that matches my unique string and then replaces old string with new string

• Search and replace using bash shell variables

 sed -i -e s%old string%$BASH_VARIABLE% /path/to/the/file
 

In order to get this done is convenient to use `sed` instead `perl` command.
Always use `-i -e` instead `-ie`, if not you will end up with another file with the same name but with an `e` at the end of the file name.

How to remove/replace a whole line

• Conditional match

 perl -pi -e '$_="" if m/my unique string/' /path/to/the/file
 

This command line removes all the lines that matches my unique string

How to work with "sed" command

Attached is a file Media:sed1line.txt with a very useful list of sed commands called One-Liners for sed. Updated version is always available at http://sed.sourceforge.net/sed1line.txt