Re^2: initializing internal regex variables?

Your comment appears to be what I needed to hear as changing the non-greedy match from /".*?"/ to /"[^"]*?"/ appears to work correctly. The negated character class was the trick.

I'm still a bit confused about why there is such a difference in what is matched, but I'm think about it some more.

Thanks for pointing me in the right direction.

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Re^3: initializing internal regex variables? by ikegami (Patriarch) on Nov 17, 2009 at 20:22 UTC
I think you expect `perl -e' $_ = qq{...\n} .qq{<a href="foo">foo</a>\n} .qq{<a href="bar">bar</a>\n} .qq{...\n}; s!(<a href=")(.?)(">bar</a>)!$1\[$2]$3!s; print; '` [download] to output `... <a href="foo">foo</a> <a href="[bar]">bar</a> ...` [download] but that's wrong. It outputs `... <a href="[foo">foo</a> <a href="bar]">bar</a> ...` [download] The pattern says to match Match the start of the string, followed by as few characters as possible (implicit leading /`.?`/), followed by the string '`<a href="`', followed by as few characters as possible, followed by the string '`">bar</a>`'. Keeping in mind that "as few characters as possible" is zero characters, let's check if the string matches: Starting at the begining of the string, Do 0 characters follow? Yes, so try to match the next atom. Does the string '`<a href="`' follow? No, so backtrack. Does 1 character follow? Yes, so try to match the next atom. Does the string '`<a href="`' follow? No, so backtrack. Do 2 characters follow? Yes, so try to match the next atom. Does the string '`<a href="`' follow? No, so backtrack. ... Do 4 characters follow? Yes, so try to match the next atom. Does the string '`<a href="`' follow? Yes, so try to match the next atom. Do 0 characters follow? Yes, so try to match the next atom. Does the string '`">bar</a>`' follow? No, so backtrack. Does 1 character follow? Yes, so try to match the next atom. Does the string '`">bar</a>`' follow? No, so backtrack. Do 2 characters follow? Yes, so try to match the next atom. Does the string '`">bar</a>`' follow? No, so backtrack. ... Do 25 characters follow? Yes, so try to match the next atom. Does the string '`">bar</a>`' follow? Yes, so try to match the next atom. We have a match!	[reply] [d/l] [select]

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Re^3: initializing internal regex variables?
by ikegami (Patriarch) on Nov 17, 2009 at 20:22 UTC

perl -e'
    $_ = qq{...\n}
        .qq{<a href="foo">foo</a>\n}
        .qq{<a href="bar">bar</a>\n}
        .qq{...\n};
    s!(<a href=")(.*?)(">bar</a>)!$1\[$2]$3!s;
    print;
'
[download]

...
<a href="foo">foo</a>
<a href="[bar]">bar</a>
...
[download]

...
<a href="[foo">foo</a>
<a href="bar]">bar</a>
...
[download]

The pattern says to match

Match the start of the string,
- followed by as few characters as possible (implicit leading /.*?/),
  - followed by the string '<a href="',
    - followed by as few characters as possible,
      - followed by the string '">bar</a>'.

Keeping in mind that "as few characters as possible" is zero characters, let's check if the string matches:

Starting at the begining of the string,
- Do 0 characters follow? Yes, so try to match the next atom.
  - Does the string '<a href="' follow? No, so backtrack.
- Does 1 character follow? Yes, so try to match the next atom.
  - Does the string '<a href="' follow? No, so backtrack.
- Do 2 characters follow? Yes, so try to match the next atom.
  - Does the string '<a href="' follow? No, so backtrack.
- ...
- Do 4 characters follow? Yes, so try to match the next atom.
  - Does the string '<a href="' follow? Yes, so try to match the next atom.
    - Do 0 characters follow? Yes, so try to match the next atom.
      - Does the string '">bar</a>' follow? No, so backtrack.
    - Does 1 character follow? Yes, so try to match the next atom.
      - Does the string '">bar</a>' follow? No, so backtrack.
    - Do 2 characters follow? Yes, so try to match the next atom.
      - Does the string '">bar</a>' follow? No, so backtrack.
    - ...
    - Do 25 characters follow? Yes, so try to match the next atom.
      - Does the string '">bar</a>' follow? Yes, so try to match the next atom.
        
        We have a match!

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