find and replace

[Sam Kreimeyer]

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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