Perl has a numeric comparison operator which compares numbers and a string comparison. Parts of a regex are grouped by enclosing them in parentheses. The comparison operator is an operator that compares two numbers. The grouping metacharacters () allow a part of a regex to be treated as a single unit. # Grouping things and hierarchical matching Here, all the alternatives match at the first string position, so the first matches. "cats" =~ /cats|cat|ca|c/ # matches "cats"Īt a given character position, the first alternative that allows the regex match to succeed will be the one that matches. "cats and dogs" =~ /dog|cat|bird/ # matches "cat"Įven though dog is the first alternative in the second regex, cat is able to match earlier in the string. Some examples: "cats and dogs" =~ /cat|dog|bird/ # matches "cat" If cat doesn't match either, then the match fails and Perl moves to the next position in the string.
If dog doesn't match, Perl will then try the next alternative, cat. At each character position, Perl will first try to match the first alternative, dog. As before, Perl will try to match the regex at the earliest possible point in the string. To match dog or cat, we form the regex dog|cat. We can match different character strings with the alternation metacharacter '|'. "Hello World" =~ m /x # matches the whole string # Matching this or that
If you're matching against $_, the $_ =~ part can be omitted: $_ = "Hello World" įinally, the // default delimiters for a match can be changed to arbitrary delimiters by putting an 'm' out front: "Hello World" =~ m!World! # matches, delimited by '!' Print "It matches\n" if "Hello World" =~ /$greeting/ The literal string in the regex can be replaced by a variable: $greeting = "World" The sense of the match can be reversed by using !~ operator: print "It doesn't match\n" if "Hello World" !~ /World/ This idea has several variations.Įxpressions like this are useful in conditionals: print "It matches\n" if "Hello World" =~ /World/ In our case, World matches the second word in "Hello World", so the expression is true. The operator =~ associates the string with the regex match and produces a true value if the regex matched, or false if the regex did not match. In this statement, World is a regex and the // enclosing /World/ tells Perl to search a string for a match. Because of this, when you want to compare two values you must specify the type of comparison to perform. A regex consisting of a word matches any string that contains that word: "Hello World" =~ /World/ # matches (In Perl, strings and numbers are mostly interchangeable with conversions happening automatically depending on how the values are used. The simplest regex is simply a word, or more generally, a string of characters. This page assumes you already know things, like what a "pattern" is, and the basic syntax of using them. This page covers the very basics of understanding, creating and using regular expressions ('regexes') in Perl. Perlrequick - Perl regular expressions quick start #DESCRIPTION perl-String-KeyboardDistance-1.01-1.2.el6.rf.noarch.html, String Comparison Algorithm, DAG packages for Red Hat. Grouping things and hierarchical matching Package, Summary, Distribution, Download.
0 kommentar(er)
