Question

I need a regular expression which would do the following –>

For example,

margin:7px 7px 7px 7px;

Should be compressed to –>

margin:7px;

(NOTE: The number may not be only 7,it can be any number. And the units can be in px|em|%|in|cm|mm|pc|pt|ex)

Answer 1

This is definitely possible in the specific case of being repeated 4 times.

Using backreferences, this is possible for a particular value of n the number of times the number is repeated. In your case, n = 4.

This one matches any “unit” value made up of only alpha characters, i.e. “px”, “em” or “foo”, plus the special case “%”. It could be made more restrictive to particular units by replacing \w* with a more specific match like (?:em|px|......)

/^(\d+(?:\.\d+)?(?:\w*|%))\s+\1\s+\1\s+\1$/

For example:

// first four examples all match
echo preg_match('/^(\d+(?:\.\d+)?(?:\w*|%))\s+\1\s+\1\s+\1$/', '7px 7px 7px 7px');
1

echo preg_match('/^(\d+(?:\.\d+)?(?:\w*|%))\s+\1\s+\1\s+\1$/', '7em 7em 7em 7em');
1

echo preg_match('/^(\d+(?:\.\d+)?(?:\w*|%))\s+\1\s+\1\s+\1$/', '5px 5px 5px 5px');
1

echo preg_match('/^(\d+(?:\.\d+)?(?:\w*|%))\s+\1\s+\1\s+\1$/', '7% 7% 7% 7%');
1

echo preg_match('/^(\d+(?:\.\d+)?(?:\w*|%))\s+\1\s+\1\s+\1$/', '5.2cm 5.2cm 5.2cm 5.2cm');
1

// different value, no match
echo preg_match('/^(\d+(?:\.\d+)?(?:\w*|%))\s+\1\s+\1\s+\1$/', '5px 5px 5px 7px');
0

// not 4 elements, no match
echo preg_match('/^(\d+(?:\.\d+)?(?:\w*|%))\s+\1\s+\1\s+\1$/', '7px 7px 7px');
0

// different unit, no match
echo preg_match('/^(\d+(?:\.\d+)?(?:\w*|%))\s+\1\s+\1\s+\1$/', '7em 7em 7em 7px');
0