What is the difference between this '/ /' and this '~ ~' and this '# #' in PHP regular expressions?

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Hello I forgot where I found this at but I ran into these 3 examples which I'm very
confused about they produce the same output. Do these 3 examples mean the same thing?
What's the difference between all of them? And I am familiar with the last one but not the other two.

<?php
$string = 'I have 2 dogs.';
if(preg_match('~\d~',$string))
{
echo 'The string above contains a numeric character.';
}
else
{
echo 'The string above does not contain a numeric character.';
}
?>

<?php
$string = 'I have 2 dogs.';
if(preg_match('#\d#',$string))
{
echo 'The string above contains a numeric character.';
}
else
{
echo 'The string above does not contain a numeric character.';
}
?>

<?php
$string = 'I have 2 dogs.';
if(preg_match('/\d/',$string))
{
echo 'The string above contains a numeric character.';
}
else
{
echo 'The string above does not contain a numeric character.';
}
?>

What I have tried:

Google did not have what I was looking for so I thought I'll get a direct answer here.

Posted 13-Jan-18 11:53am

Member 13605567

Updated 14-Jan-18 0:23am

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Thomas Daniels · Answer 1 · 2018-01-14T00:23:00

The chars at the start and the end are delimiters (preg_match requires them), and the pattern is inside the delimiters.

PHP: Delimiters - Manual[^]

Quote:
When using the PCRE functions, it is required that the pattern is enclosed by delimiters. A delimiter can be any non-alphanumeric, non-backslash, non-whitespace character.

Often used delimiters are forward slashes (/), hash signs (#) and tildes (~).

So to answer your question "What's the difference?": the difference is only the delimiters, the patterns themselves have no difference.

But what's the purpose of allowing to choose a delimiter? That's also explained in the manual I linked above:

Quote:
If the delimiter needs to be matched inside the pattern it must be escaped using a backslash. If the delimiter appears often inside the pattern, it is a good idea to choose another delimiter in order to increase readability.

Patrice T · Answer 2 · 2018-01-13T12:16:00

Quote:
Hello I forgot where I found this at but I ran into these 3 examples which I'm very confused about they produce the same output.

And that same output is?
If the output is 'The string above does not contain a numeric character.', it looks perfectly normal to me.
As far as I can see those characters are not RegEx control, they simply matched like any other chars.

Just a few interesting links to help building and debugging RegEx.
Here is a link to RegEx documentation:
perlre - perldoc.perl.org[^]
Here is links to tools to help build RegEx and debug them:
.NET Regex Tester - Regex Storm[^]
Expresso Regular Expression Tool[^]
RegExr: Learn, Build, & Test RegEx[^]
This one show you the RegEx as a nice graph which is really helpful to understand what is doing a RegEx:
Debuggex: Online visual regex tester. JavaScript, Python, and PCRE.[^]

What is the difference between this '/ /' and this '~ ~' and this '# #' in PHP regular expressions?

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