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The last grouping of metacharacters in the Special characters menu are the Posix metacharacters. Posix stands for Portable Operating System Interface and it's a form of writing expressions that's slightly different from what we've seen so far. So let's take a look at the difference between Posix and some of what we've seen so far. I am on page 3 of this document and my cursor is within the Body Text paragraph style. I am going to right-click on that style name, choose Edit Body Text from the Context menu and in the Paragraph Style options, I will switch to GREP style.
I am going to create a new GREP style just so we can gain access to this menu at the end of the To text field and take a look at the Posix metacharacters. Down at the bottom of the list is Posix and there are a handful of metacharacters here that are a different form of Wildcard. Many of them overlap Wildcards we've already seen in this menu. So they're repetitive and just a different way of saying something we've already covered in previous movies. However, there are a couple of Posix meta- characters that could prove very useful.
I will just quickly go down the list. They're named slightly differently, so it's a little bit easier to figure out what a Posix metacharacter means just by looking at it. The first one alnum is any alphanumeric character, so any upper or lowercase letter or any digit. Alpha is any alphabetical character, upper or lowercase. Digit is any digit. Lower is any lowercase character. Punct is any punctuation character. Space is any white space. Upper is any uppercase character. Word is any word character.
So this is a lot of overlap between Wildcards we've seen in previous movies. The only thing that's unique here, at this point is punct, which specifies punctuation in one fell swoop. You don't have to create a character set that includes every possible bit of punctuation. It's automatically handled by this Posix metacharacter. So that's a very useful one. The next one down here, xdigit, this speaks to the computer programming origins of GREP in general and certainly of Posix. It refers to any hexadecimal digits.
So it is placed inside of a page layout application. It doesn't really reveal itself, I don't think, for most of us. But if you use hexadecimal digits in your documents for some reason and want to apply GREP style to them, this is the metacharacter for you. The last Posix metacharacter is even different than all the other ones, which are different from the metacharacter syntax we've seen so far and the example in this list is just two opening square brackets an equal sign the letter A and another equal sign and two closing square brackets.
Let's take a quick look at this one, just so we can understand what it is. As it appeared in the menu with the A, that is just a visual cue for your benefit of the syntax for this type of metacharacter. If I actually type in 'a' here and then, from the Apply Style menu, I choose my Red character style. Let's take a look at what this does on the page. I will click off here and notice that it has matched every lowercase A and every uppercase A. Beyond that, and what you can't see here, because there are no instances of it, is that it will also match every accented A. Everything with an accent grave, everything with an accent acute, any variation, any equivalent of an A that's defined by that typeface is going to be matched by this character.
So it's very broad if you're working with text that has a lot of accented characters and you need to account for every variation of A or every variation of an accented vowel or any character with multiple variations, this is the way to do it. It's also a way to account for, at a minimum, both upper and lowercase instances of that letter. The same would apply if it was C, upper and lowercase C's and the accented C's and so on. So whatever you put in there any single character, you're going to get every variation for that character. So that's a unique Posix metacharacter that's very useful.
I am going to clear that out here and the other Posix metacharacter I mentioned earlier as being unique to Posix, and very useful, is the punct Posix metacharacter, which accounts for all punctuation, and there is an example from a previous movie where we were constructing negative character classes to find anything that's not a vowel. If the goal was actually to find only consonants, defining a negative character class as anything that isn't a vowel grabbed up a lot more text than we intended.
It grabbed punctuation and white spaces and any number of other things. So let's reconstruct that character set using an opening square bracket, the carrot symbol, which means match everything in this character set that isn't what I type following this symbol. And we put in 'aeiou' and, in uppercase, 'AEIOU' and close that off with a closing square bracket. That's a negative character set that says find anything that is not an upper or lowercase vowel. I am going to change the character style to yellow highlight because that's the only way I can see the white spaces that it finds as well.
This is what we've found. It excluded vowels, but included every single other type of character. If I were to try to eliminate all of the punctuation, I'd have to remember every potential punctuation mark there is in the alphabet. That's not time well spent on my part, so I can take advantage of that punctuation Posix metacharacter and include it inside of this character class, along with these standard characters. So, I am going to the Special characters menu, down to Posix and pick that punct metacharacter.
Now there is one problem that I am going to reveal, before we even click off here. All Posix metacharacters are in fact character classes already. They have two square brackets on either side of the expression and when they're just used by themselves, that's fine. That's exactly how they're supposed to appear. But if you put a Posix character inside of a character class, you need to get rid of that extra square bracket at the end and the extra square bracket at the beginning. When I do that and click off here, notice all my punctuation has been deselected because I've defined punctuation, any form of punctuation, as something to be skipped over and that makes this easier to define.
Now I can put in any white space and eliminate that. At this point, I've now described every consonant and the punctuation metacharacter made it much quicker and easier to do. So even though Posix expressions are all the way at the bottom of the menu, don't follow the same syntax as most of the other metacharacters we've seen and often repeat the functionality of many Wildcards, these punctuation and character equivalent Posix expressions, in this list, are hidden gems that describe character sets that are otherwise very difficult to describe with conventional metacharacters.
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