When you do search and replace, the replace section is literal not a pattern match.  So piece by piece:

s/ # This means match the first section and replace with the second

\.JPG$/  # This means a literal '.' at any point in the string followed by 'JPG' then the end of the line

.jpg/ # This is the string to replace the previous regex with '.jpg'

--

Paul Mooring

Systems Engineer and Customer Advocate

www.opscode.com

From: Michael Havens <bmike1@gmail.com>
Reply-To: Main discussion list <plug-discuss@lists.plug.phoenix.az.us>
Date: Tuesday, September 11, 2012 9:42 AM
To: Main discussion list <plug-discuss@lists.plug.phoenix.az.us>
Subject: Re: find and replace

Hate to resurrect old stuff but in

   rename 's/\.JPG$/.jpg/' *.JPG

is this saying to s(earch)/(for the string).JPG$/(replace with).jpg/ ? Why does one not need the escape character (\) before the period here or before the final JPG? What does the *.JPG at the end signify?

:-)~MIKE~(-: 

On Tue, Feb 21, 2012 at 7:32 AM, Sam Kreimeyer <skreimey@gmail.com> wrote:

Here's a pdf of a quick guide to regular expressions
http://www.addedbytes.com/download/regular-expressions-cheat-sheet-v1/pdf/

Basically, it's a format for defining search patterns that supports special meanings for certain characters. For instance:

a - finds any string like "a"
a. - finds any string like "a" plus any other character except a new line (matches "aa", "ab", "ac", etc)
a.* - finds any string like "a" plus zero or more characters except a new line (matches "aa", "abcdefghijk")
Other special characters can further modify this behavior.

So here's an explanation of the earlier command.

's/\.JPG$/.jpg/' *.JPG

Basic search and replace format s/[string we search for]/[string to replace matches with]/

"\.JPG$" - Because "." is special, we escape it with "\" to keep the regex from interpreting it, so the "." will be treated literally. "JPG" is what we're looking for. Placing a "$" at the end of the string tells the regex to match the string only at the end of the strings you're searching. This means that you will match "example.JPG" but not "JPG.example".

".jpg" - This is our replacement string. This is what goes in the place of every match we find.

"*.JPG" - while this isn't part of the regex, "*" is a wildcard (can be substituted for any number of characters).

Hope that helps!

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