![]() ![]() The plus sign is a multiplier that says "use one or more of the preceding." A character class matches a single character, one of the characters in the class. We used a character class, followed by a plus sign: (+). Now let's look inside that subexpression: (.). If you're not sure what goes in which group, count the open parentheses.) We could even have nested them, if we needed to. (If we had more groups, the second one would be \2 and so on. That makes the subexpression available in the Replace string as \1. Then, we used parentheses to group a subexpression: width\=(.). That simply says: "width" followed by "an equal sign, no special meaning, please." We followed with an escaped punctuation mark: width\=. That finds the string "width" (followed by ".", which is part of this explanation, not part of regex-it means we'll get there next). Time to create a test file and try this out. That would be \d+px (assuming all your widths were in pixels). If you are not sure if the equal sign has a special regex meaning (it doesn't), a safer version is width\=.īut what next? You'll have some digits and the letters "px". To keep it simple, assume that your width specs are all on a single line and don't include embedded quotes. We want to replace it with the same specification but the width value must be in single quotes. Let's return to our problem: we want to find all occurences of "width=" followed by a width specification. The characters inside the group that starts with the first "(" is called either "$1" (in Perl and languages that copy Perl closely) or "RegExp.$1", in JavaScript or "\1" in the Replace string in an editor such as Notepad++. When a regex contains parentheses, the characters matched within the parentheses can be used later. ![]() matches any character EXCEPT an uppercase letter. dg matches any d.g string ("d", then any character, then "g") except "dig", "dog" or "dug". ![]() ![]() It means "match any character EXCEPT one of these. matches any uppercase letter.Ī caret ("^") in the first position of a character class negates the class. You may use hyphens to indicate ranges of characters. The pattern dg matches "dig" or "dog" or "dug". (a|b) means an "a" or a "b".Įnclosing a list of characters in brackets means, "match exactly one of these characters." Example. ? (zero or one) the preceding character is optional.+ (one or more) \d+ is "one or more digits", a pattern that matches every positive decimal integer.Some regex characters provide a repetition factor, called a "multiplier". \D any character EXCEPT a decimal digit.The single, lowercase letters that identify special character classes may be reversed in meaning by using the uppercase letter: (If you are not sure, which is often the case, "escape" the punctuation mark-precede it with a backslash.) Whether or not they are special, if you want the mark itself, precede it with a backslash. Punctuation marks sometimes have a special meaning. \w (w stands for "word") any alphabetic (upper or lowercase), digit (0 through 9) or an underscore.\s (two characters, read as "escape s") matches any whitespace (space, tab, return or newline).a the letter "a" matches itself-most characters match just themselves.So here's a tiny regex summary (there are whole books written on the subject!) to get you started. You need to change the fixed part but preserve the variable part. You have some text to find, part of which is fixed and part of which is variable. in XHTML, they are mandatory.) A simple Find/Replace would do the trick, but you've also got width=60px and lots of other widths. You want that upgraded to an XHTML compatible attribute width='120px'. The "Find" part of a Find/Replace dialog is one simple example. Regular expressions are used for matching string patterns. If you've never used regex before, we won't teach you too much in this one short page, but we'll get you started with a basic use. One of the great features of programmer's editor Notepad++ is that it matches these old veterans' regex strengths without hiding them in a forest of cryptic commands. One of the features of the great old programming editors (with legendary Unix names like Vi and Emacs) was their ability to use regular expressions (aka regex) in search and replace operations. ![]()
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