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Why do PHP regexes have the surrounding delimiters? It seems like it would be more clear if any pattern modifiers were passed in as a parameter to whatever function was being used.
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Delimiters. The first element of a regular expression is the delimiters. These are the boundaries of your regular expressions. The most common delimiter that you'll see with regular expressions is the slash ( / ) or forward slash.
A delimiter is a sequence of one or more characters for specifying the boundary between separate, independent regions in plain text, mathematical expressions or other data streams. An example of a delimiter is the comma character, which acts as a field delimiter in a sequence of comma-separated values.
A delimiter can be any non-alphanumeric, non-backslash, non-whitespace character. Leading whitespace before a valid delimiter is silently ignored. Often used delimiters are forward slashes ( / ), hash signs ( # ) and tildes ( ~ ).
In computer programming, a delimiter is a character that identifies the beginning or the end of a character string (a contiguous sequence of characters). The delimiting character is not part of the character string.
The reason for the delimiter is to put flags after the pattern. Arguably flags could be passed as a separate parameter (Java can do it this way) but that's the way Perl did it originally (and sed/awk/vi before it) so that's how it's done now.
Don't use forward slashes: they're too common. Personally I nearly always use the ! character. I'm hardly ever looking for that.
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There is no technical reason why it has to be like this.
As noted in a comment, the underlying library does not require that flags be passed as part of the regexp - in fact, the extension has to strip these off and pass them as a separate argument.
It appears as though the original implementer was trying to make it look like grep/sed/awk/perl/etc so that it is more familiar to programmers coming from those tools.
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