Difference between revisions of "Perl-regex"

__NOTOC__

= Perl Regex =

== How to search and replace a word or phrase ==

* '''All matches'''

<pre><nowiki>

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

</nowiki></pre>

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'''

<pre><nowiki>

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

</nowiki></pre>

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'''

<pre><nowiki>

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

</nowiki></pre>

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'''

<pre><nowiki>

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

</nowiki></pre>

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