I am learning regular expressions and I am trying find this string day1otlk_XXXX.gif where the 4 X's will be 3 to 4 random digits. This is what I have so far am I close?
qr/day1otlk_\d++\.gif/i
+1
A:
Kinda close. You have the \d for digits.
Do you know what the range operator for regular expressions is?
Axeman
2010-08-20 19:24:31
+1
A:
Very close. This should do it...
day1otlk_\d{3,4}\.gif
The braces {} allow you to specify a ranged number of repeated characters {3,4} or an exact number like {4}.
Steve Wortham
2010-08-20 19:24:43
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A:
the regex should be /day1otlk_(\d{3,4})\.gif/, maybe /i for case-insensitivity. if it's in a string you might want /\bday1otlk_(\d{4})\.gif\b/ instead for stuff like "asdjklfhlday1otlk_5242.gifiasdytoi", which you probably don't want.
the {3,4} means that there need to be between three and four digits, and the parentheses to capture those four digits in \1 or $1.
(bonus un-asked-for answer: if you need exactly three or, say, five, you can't do that. {3,5} will get between three and five. you'd need \d{3}\d{2}? or something of the sort.)
sreservoir
2010-08-20 19:24:44
For the bonus: `(\d{3}|\d{5})`.
Svante
2010-08-20 19:46:59
that works too, yes. probably works better in pathological cases, too.
sreservoir
2010-08-20 19:51:35
@Svante: Even better would be to optimize out the common part: `\d{3}(\d{2})?`
Ether
2010-08-20 20:24:37
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A:
You specify a range quantifier with curly braces:
qr/day1otlk_\d{3,4}\.gif/i
Eric Strom
2010-08-20 19:26:11
+1
A:
You can specify that there will be 3 or 4 digits with the following:
day1otlk_\d{3,4}\.gif
The {} is a repetition modifier. It's a little more precise than * or +. You can use it to specify an exact number of repetitions of the preceding pattern or a range of repetitions.
a{m} - exactly m a’s
a{m,} - at least m a’s
a{m,n} - at least m but at most n a’s
Bill the Lizard
2010-08-20 19:26:54