I'm trying to understand the backslash and how to use escaping like: \ in regular expressions.
I've read that when using strings its named to escape a string.
But what does that actually mean?
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The Great Escapism (Or: What You Need To Know To Work With Text Within Text)deceze– deceze ♦2016-05-06 05:29:36 +00:00Commented May 6, 2016 at 5:29
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3 Answers
Many characters in regular expressions have special meanings. For instance, the dot character '.' means "any one character". There are a great deal of these specially-defined characters, and sometimes, you want to search for one, not use its special meaning.
See this example to search for any filename that contains a '.':
/^[^.]+\..+/
In the example, there are 3 dots, but our description says that we're only looking for one. Let's break it down by the dots:
- Dot #1 is used inside a "character class" (the characters inside the square brackets), which tells the regex engine to search for "any one character" that is not a '.', and the "+" says to keep going until there are no more characters or the next character is the '.' that we're looking for.
- Dot #2 is preceded by a backslash, which says that we're looking for a literal '.' in the string (without the backslash, it would be using its special meaning, which is looking for "any one character"). This dot is said to be "escaped", because it's special meaning is not being used in this context - the backslash immediately before it made that happen.
- Dot #3 is simply looking for "any one character" again, and the '+' following it says to keep doing that until it runs out of characters.
So, the backslash is used to "escape" the character immediately following it; as such, it's called the "escape character". That just means that the character's special meaning is taken away in that one place.
Now, escaping a string (in regex terms) means finding all of the characters with special meaning and putting a backslash in front of them, including in front of other backslash characters. When you've done this one time on the string, you have officially "escaped the string".
Comments
Say you try to print out a string, let's say "this\that". That \ character is recognized as a special character. I'm not sure about regex, but say in Java or C, \t will tab the rest of the string over, so it would print as
this hat
But the \ "escapes" a character from the string, deriving it of regular meaning, so using "this\that" instead would result in
this\that
I hope this helped.
Comments
The backslash (\) in a regular expression indicates one of the following:
The character that follows it is a special character, as shown in the table in the following section. For example, \b is an anchor that indicates that a regular expression match should begin on a word boundary, \t represents a tab, and \x020 represents a space.
A character that otherwise would be interpreted as an unescaped language construct should be interpreted literally. For example, a brace ({) begins the definition of a quantifier, but a backslash followed by a brace (\{) indicates that the regular expression engine should match the brace. Similarly, a single backslash marks the beginning of an escaped language construct, but two backslashes (\) indicate that the regular expression engine should match the backslash.
