This page lists the regular expression syntax accepted by RE2. These changes make the regular expressions more concise, and sometimes more cryptic, but not more powerful. Newer regular expression facilities (notably Perl and those languages that have copied it) have added many new operators and escape sequences. A regular language is a set of strings that can be matched in a single pass through the text using only a fixed amount of memory. Newer regular expression facilities (notably Perl and those languages that have copied it) have added many new operators and escape sequences. This subset suffices to describe all regular languages. The syntax described so far is most of the traditional Unix egrep regular expression syntax. Some examples: ab|cd is equivalent to (ab)|(cd) ab\ is equivalent to a(b\). Explicit parentheses can be used to force different meanings, as in arithmetic expressions. The operator precedence, from weakest to strongest binding, is first alternation, then concatenation, and finally the repetition operators. The metacharacters \, +, and ? are repetition operators: e 1 \ matches a sequence of zero or more (possibly different) strings, each of which match e 1 e 1 + matches one or more e 1 ? matches zero or one. Two regular expressions can be altered or concatenated to form a new regular expression: if e 1 matches s and e 2 matches t, then e 1 | e 2 matches s or t, and e 1 e 2 matches st. For detailed information, see Grouping constructs in regular expressions. You can use captured groups within the regular expression itself (for example, to look for a repeated word), or in a replacement pattern.
#Regular expression not end with plus#
To match a metacharacter, escape it with a backslash: \+ matches a literal plus character. A capture group delineates a subexpression of a regular expression and captures a substring of an input string. So to find a 'foo' not preceded by a '.' would be. Except for the metacharacters like \*+?()|, characters match themselves. The (circumflex or caret) inside square brackets negates the expression.
The simplest regular expression is a single literal character. When a string is in the set described by a regular expression, we often say that the regular expression matches the string. You can run find -regextype help to find out what is supported on your system.Regular expressions are a notation for describing sets of character strings. POSIX classes are intended for use within character classes, so you use them within square brackets. Strings that end with a particular substring: 4. ‘findutils-default’, ‘awk’, ‘egrep’, ‘ed’, ‘emacs’, ‘gnu-awk’, ‘grep’, ‘posix-awk’, ‘posix-basic’, ‘posix-egrep’, ‘posix-extended’, ‘posix-minimal-basic’, ‘sed’ Show records where the name ends with a 'H' 3. maxdepth 1 -regextype egrep -regex '\./.*\.txt' You can specify a -regextype, for example: find. maxdepth 1 -regex '\./.*\.txt' -exec ls -lah \ įind supports a couple of different regex flavors. If you want to get the output of ls, then you can use -exec ls like this: find. The digit classes are same as for globbing, just that you need ^ instead of ! to invert the character class. txt, because the regex would otherwise also match Atxt.
is a special character matching any character, but here we really want a dot, that's why we escape it with a backslash. The regex starts with \./ to cope with that. If you use this regex with anchors to validate the email address entered on your order form. The 4 at the end of the regex restricts the top-level domain to 4 characters. To only find files in the current directory, you can disable recursion with -maxdepth 1.įind matches against the filename with path, that's why the filenames start with. The regular expression I receive the most feedback, not to mention bug reports on, is the one you’ll find right on this site’s home page: b A-Z 0-9.+. maxdepth 1 -regex '\./.*\.txt'įind is recursive by default, but ls is not. If you really want to use regular expressions, you can use find -regex like this: find. Regular expressions are a lot more powerful than that. What it supports is filename expressions ( Globbing), a form of wildcards. Bash, and thus ls, does not support regular expressions here.
The question asked for regular expressions.