I wrote ā€œMaking Regular Expressions Your Friendsā€ while I was at RSI (and while it was still RSI). Regular expressions are a ā€œlittle languageā€ embedded inside IDL (and most other modern languages) with very powerful string processing capabilities. In the whitepaper, all the details of IDLā€™s implementation of regular expressions are explained with examples (including the undocumented stuff). Also included in the download is the STR_REPLACE routine (download).

STR_REPLACE can do search and replace actions on strings. For example,

IDL> print, str_replace('data001.dat', 'data', 'precip')
precip001.dat

replacing ā€˜dataā€™ with ā€˜precipā€™ in ā€˜data001.datā€™. The cool part about it is you can replace one regular expression with another, even evaluating IDL expressions in the process. For example,

IDL> search = '([[:alpha:]]+)([0-9]+)'
IDL> replace = 'strupcase(''$1'') + string(fix($2), format=''(Z0)'')'
IDL> print, str_replace('precip032.dat', search, replace, /evaluate)
PRECIP20.dat

Read the whitepaper whitepaper if thatā€™s a bit too dense to follow.

UPDATE 1/22/14: Updated links.

UPDATE 1/23/14: I recommend using MG_STREPLACE instead of the STR_REPLACE shown above.