□ Note: It doesn’t harm to escape the dot regex or any other special symbol within the character class-Python will simply ignore it! So if you want to match the '^' symbol, you can use it as the non-first character in a character class (e.g., pattern ). However, it loses its special meaning when it’s not the first character. It has another special meaning when used as the first character of the character class (= negative character class). The hat special character '^' means start-of-the-line regex. Python knows that the minus as the first or last character cannot signal a range because the range wouldn’t be opened or closed (e.g., patterns or ). However, the minus is also seen as a normal literal character if it’s the first or last value in a character class. The Minus Characterįor example, the minus '-' character has a special meaning within the character class, it’s the range character in the pattern ''. The reason is that in a character class, any character except ^, -, ] or \ are literals, i.e., they’ve lost their special meaning if they had any. This holds for the Python re and the newer Python regex modules. No, you don’t need to escape the dot character in a character class. In other words, the pattern 'hello\.' would match the string 'hello.' but not the string 'hello!'.ĭo you need to escape the dot character in a Python regex character class? Answer For example, to match the actual dot '.' character, you need to design a pattern with escaped dot '\.'. Special characters such as the dot character often need to be escaped in a regex pattern if you want to match them.For example, the pattern 'ct' will match the strings 'cat', 'cut', or 'czt'. The character class is a set of characters: if you use it in a regex pattern, the engine will match exactly one character from the set.For example, the pattern 'c.t' will match the strings 'cat', 'cut', or 'czt'. in regular expressions matches any character excluding the newline character. Escape a string: "$(printf '%s' "$string" | sed 's/[.Recap the following regular expression concepts (more details in the article below):.Commands: grep -E, sed -E (old GNU versions: sed -r).Example: Instead of '\[' you can write \\[ (alternatively: "\[" or "\\[") in Bourne compatible shells like bash but this is another story. The characters which are special in some contexts like ^ special at the beginning of a (sub-)expression can be escaped in all contexts.Īs others wrote: in shell if you do not enclose the expression between single quotes you have to additionally escape the special characters for the shell in the already escaped regex. In all the cases special characters are escaped by backslash \. There are multiple types of regular expressions and the set of special characters depend on the particular type. Specific programs (using regexes, perl, awk) could have additional requirements on escaping. The here-document representsĪnother form of quoting see Here-Document. The various quoting mechanisms are the escape character, That is, these characters may be special depending on conditionsĭescribed elsewhere in this volume of IEEE Std 1003.1-2001: * ? [ # ˜ = % Represent themselves: | & ( ) $ ` \ " ' Īnd the following may need to be quoted under certain circumstances. The application shall quote the following characters if they are to Reserved words from being recognized as such, and prevent parameterĮxpansion and command substitution within here-document processing Meaning of the special characters in the next paragraph, prevent Quoting can be used to preserve the literal Quoting is used to remove the special meaning of certain characters or In your example [ must be quoted as an argument for grep but not echo.
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