Regex to match text between specified delimiters? (I just can't get it myself)

Question

Hi,

I've been googling & trying to get this myself but can't quite get it...

QUESTION: What regular expression could be used to select text BETWEEN (but not including) the delimiter text. So as an example:

Start Marker=ABC
Stop Marker=XYZ

---input---
This is the first line
And ABCfirst matched hereXYZ
and then
again ABCsecond matchXYZ
asdf
------------

---expected matches-----
[1] first matched here
[2] second match
------------------------

Thanks

Answer 1

Standard or extended regex syntax can't do that, but what it can do is create match groups which you can then select. For instance:

ABC(.*)XYZ

will store anything between ABC and XYZ as \1 (otherwise known as group 1).

If you're using PCREs (Perl-Compatible Regular Expressions), lookahead and lookbehind assertions are also available -- but groups are the more portable and better-performing solution. Also, if you're using PCREs, you should use *? to ensure that the match is non-greedy and will terminate at the first opportunity.

You can test this yourself in a Python interpreter (the Python regex syntax is PCRE-derived):

>>> import re
>>> input_str = '''
... This is the first line
... And ABC first matched hereXYZ
... and then
... again ABCsecond matchXYZ
... asdf
... '''
>>> re.findall('ABC(.*?)XYZ', input_str)
[' first matched here', 'second match']

Answer 2

/ABC(.*?)XYZ/

By default, regular expression matches are greedy. The '?' after the . wildcard character, denotes a minimal match, so that the first match is this:

first matched here

...instead of this:

first matched hereXYZ
and then
again ABCsecond match

Answer 3

You want the non-greedy match, .*?

while( $string =~ /ABC(.*?)XYZ/gm ) {
  $match = $1;
}