The symbol \b matches the empty string at the edge of a word, and \B matches the empty string provided it’s not at the edge of a word.Ī regular expression may be followed by one of several repetition operators: ? The symbols \ respectively match the empty string at the beginning and end of a word. The caret ^ and the dollar sign (« $«) are metacharacters that respectively match the empty string at the beginning and end of a line. The symbol \w is a synonym for ] and \W is a synonym for ]. Finally, to include a literal - place it last. Similarly, to include a literal ^ place it anywhere but first.
To include a literal place it first in the list. (Note that the brackets in these class names are part of the symbolic names, and must be included in addition to the brackets delimiting the bracket list.) Most metacharacters lose their special meaning inside lists. For example, ] means, except the latter form depends upon the C locale and the ASCII character encoding, whereas the former is independent of locale and character set. Their names are self explanatory, and they are, ,, ,, ,, ,, , and. To obtain the traditional interpretation of bracket expressions, you can use the C locale by setting the LC_ALL environment variable to the value C.įinally, certain named classes of characters are predefined within bracket expressions, as follows. Many locales sort characters in dictionary order, and in these locales is typically not equivalent to it might be equivalent to, for example. For example, in the default C locale, is equivalent to. It matches any single character that sorts between the two characters, inclusive, using the locale’s collating sequence and character set.
Within a bracket expression, a range expression consists of two characters separated by a hyphen («-«). For example, the regular expression matches any single digit. It matches any single character in that list if the first character of the list is the caret ^ then it matches any character not in the list.
Any metacharacter with special meaning may be quoted by preceding it with a backslash.Ī bracket expression is a list of characters enclosed by and. Most characters, including all letters and digits, are regular expressions that match themselves. The fundamental building blocks are the regular expressions that match a single character. The following description applies to extended regular expressions, which are used in egrep differences for basic regular expressions are summarized afterwards. In other implementations, basic regular expressions are less powerful. Grep understands two different versions of regular expression syntax: « basic» and « extended.» In GNU grep, there is no difference in available functionality using either syntax. Regular expressions are constructed analogously to arithmetic expressions, by using various operators to combine smaller expressions. Совмещение r и python: зачем, когда и как?Ī regular expression is a pattern that describes a set of strings.
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