Question 250682 in PHP Question posted in
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Php – Perl match string containes dot too

I need to match a string which contains dot (.) and no dot.

Here are the sample patterns:

res:shanghai:45610
res:chicago.usa:57450

Regex I’m using:

res:[w]{4,15}:[1-9][0-9]*

It matches only res:shanghai:45610, but it should match both.

Since the second pattern contains a dot (.) between chicago.usa, it doesn’t match.

How do I alter regex to match res:chicago.usa:57450 too. Specifically, it should allow a single dot in the middle of word characters, while still restricting the length of the field to a min 4 and a max 15 characters including the dot.

Above test case on regex101.

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3

Answers


  1. 0

    Just add the dot to the character class:

    res:[.w]{4,15}:[1-9][0-9]*

    But it would also match strings with all dots.

    res:....:1
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  2. 0

    Basically, you want the middle part to match both

    [w.]{4,15}

    and

    w+(?:.w+)?

    Lookaheads can be used to perform "AND" operations.

    res:(?=[w.]{4,15}:)w+(?:.w+)?:[1-9][0-9]*

    Another possibility is doing the length check outside of the regex.

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  3. 0

    As mentioned, one can check the length outside of regex. Since the dot can show up only after a character and has to be followed by a character the pattern is extremely simple

    w+.?w+

    and altogether, for example

    if ( /res:(w+.?w+):[1-9][0-9]*/ and length $1 >= 4 and length $1 <= 15 )

    The one advantage of this is the pattern’s simplicity — that it avoids the advanced and complex combined use of lookaheads and consuming patterns.

    Since v5.32 we can also write the two conditions as a "chained comparison"

    if ( /res:(w+.?w+):[1-9][0-9]*/ and 4 <= length $1 <= 15 )

    Also see this discussed in perlop, Operator-Precedence-and-Associativity

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