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Re: Regular Expressions
JD Smith wrote:
> IDL> print, stregex(st,'(^|[^l])l($|[^l])')
> which means "a character that is not 'l', or the beginning of the
> string, followed by an 'l', followed by a character that is not 'l', or
> the end of the string". Aren't you glad Ken Thompson didn't decide
> originally to develop regexps in english?
> This will also work on
> IDL> st = "let's all go the the movies"
Thanks. But I now realize that my original formulation was not quite
correct, since the above expression (usually!) returns the position of the
character *before* the 'l', so to get the position of the first single 'l'
one has to add 1
IDL> l_position = stregex(st,'(^|[^l])l($|[^l])') + 1
Unfortunately, if 'l' is the first character, then you *don't* want to add
the 1. (The expression stregex(st,'(^|[^l])l($|[^l])') returns a value of
0 for both st ='long days' and st ='slow nights'. )
One solution is to forget about the beginning of string anchor and just
concatenate a blank to the beginning to the string
IDL> l_position = stregex(' ' + st,'[^l]l($|[^l])')
P.S. The real-life problem I am working on deals not with 'l' but with
apostrophes. I am trying to speed up the processing of FITS header
values, where is a string is delineated by non-repeating apostrophes, and a
possessive is indicated by a double apostrophe.
VALUE = 'This is Wayne''s FITS value' / Example string field