Determine if string is all caps with regular expression

Question

How can you determine if a string is all caps with a regular expression. It can include punctuation and numbers, just no lower case letters.

Answer 1

$str="ABCcDEF";
if ( preg_match ("/[a-z]/",$str ) ){
    echo "Lowercase found\n";
}

Answer 2

If you want to match the string against another regex after making sure that there are no lower case letters, you can use positive lookahead.

^(?=[^a-z]*$)MORE_REGEX$

For example, to make sure that first and last characters are alpha-numeric:

^(?=[^a-z]*$)[A-Z0-9].*[A-Z0-9]$

Answer 3

Basic:

^[^a-z]*$

Exclude empty lines:

^[^a-z]+$

Catering for exclusion of non-english chars (e.g. exclude a string containing à like 'VOILà'):

^\P{Ll}*$

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Expressions (e.g. JS):

Single line:

/^[^a-z]*$/

Multi line:

/^[^a-z]*$/m

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Theory:

[a-z] matches a character that is a,b,c,...z

[a-z]* matches a series of characters that are a,b,c,...z

^[a-z]* matches a series of characters that are not a,b,c...z

^[^a-z]*$ matches a string only containing a series of characters that are not a,b,c,...z from beginning to end.

^[^a-z]+$ ensures that there is at least one character that is not a,b,c,...z, and that the remaining characters are not a,b,c,...z in the string from beginning to end.

^\P{Ll}*$ matches all Unicode characters in the 'letter' group that have an uppercase variant - see https://www.regular-expressions.info/.