Q:

Check string for all lowercase letters in PowerShell

I want to be able to test if a PowerShell string is all lowercase letters.
I am not the worlds best regex monkey, but I have been trying along these lines:
if ($mystring -match "[a-z]^[A-Z]") {
    echo "its lower!"
}

But of course they doesn't work, and searching the Internet hasn't got me anywhere. Is there a way to do this (besides testing every character in a loop)?

A:

PowerShell by default matches case-insensitively, so you need to use the -cmatch operator:
if ($mystring -cmatch "^[a-z]*$") { ... }

-cmatch is always case-sensitive, while -imatch is always case-insensitive.
Side note: Your regular expression was also a little weird. Basically you want the one I provided here which consists of

The anchor for the start of the string (^)
A character class of lower-case Latin letters ([a-z])
A quantifier, telling to repeat the character class at least 0 times, thereby matching as many characters as needed (*). You can use + instead to disallow an empty string.
The anchor for the end of the string ($). The two anchors make sure that the regular expression has to match every character in the string. If you'd just use [a-z]* then this would match any string that has a string of at least 0 lower-case letters somewhere in it. Which would be every string.

P.S.: Ahmad has a point, though, that if your string might consist of other things than letters too and you want to make sure that every letter in it is lower-case, instead of also requiring that the string consists solely of letters, then you have to invert the character class, sort of:
if ($mystring -cmatch "^[^A-Z]*$") { ... }

The ^ at the start of the character class inverts the class, matching every character not included. Thereby this regular expression would only fail if the string contains upper-case letters somewhere. Still, the -cmatch is still needed.

A:

If your test is so simple, you can and probably should avoid the use of regular expressions:
$mystring -ceq $mystring.ToLower()

