regex preg_match for digit in middle for a string

Question

ddw_0_op1
ddw_1_op1
ddw_2_op1
ddw_3_op1
ddw_4_op1

in these strings of array how i can extract or preg_match only the number in middle that increase . t

Answer 1

I would break the string on underscore:

$parts = explode('_', $string);
$middle = $parts[1];

Answer 2

If the number never exceeds a single digit, you could simply use $str[4] to get the fifth character of the string (your digit). On the other hand, however, if the numbers continue indefinitely, you could use either of the following regular expressions.

Option 1

See regex in use here

(?<=_)\d+(?=_)

• (?<=_) Positive lookbehind asserting what precedes is _
• \d+ Matches one or more digits
• (?=_) Positive lookahead asserting what follows is _

Option 2

See regex in use here: This method uses fewer steps than the previous.

_\K\d+(?=_)

• _ Match this literally
• \K Resets the starting point of the reported match. Any previously consumed characters are no longer included in the final match
• \d+ Matches one or more digits
• (?=_) Positive lookahead asserting what follows is _

Answer 3

use the preg_match function:

$str = "ddw_01_fdfd";
preg_match('/.+_([0-9]+)_.+/', $str, $matches);
echo $matches[1];

Output:

01

Another way to do it is by explode the string by _:

$xpl = explode('_', $str);
$middleStr = $xpl[1];

The explode function splits a string by string, in that case create an array made by all substring contained in $str dividing them by _.

Try it here.