文档介绍：Regular Expressions
Luo Dan
2006-7-26
2017/11/12
1
Regular Expressions
Contents
Give a simple definiens
Give a simple example
Basic about perl regex syntax
A job to do immediately
(a email address: @)
Discuss
2017/11/12
2
Regular Expressions
Regex-Regular Expressions
A regular expression (regex or regexp for short) is a special text string for describing a search pattern. You can think of regular expressions as wildcards on steroids.
For Example: *.txt
It can be written in Perl, PHP, Java, a .NET language or a multitude of other languages.
Here, I only describe regex in Perl.
2017/11/12
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Regular Expressions
A Simple Example
#!/bin/perl
die ("You don't input a file name!\n") if !defined($ARGV[0]);
print ("Warning: without file!\n") if ($ARGV[0] !~ m/\w*/);
open (FILE, "<$ARGV[0]") or die ("Cannot open the file!\n");
***@lines = <FILE>;
close(FILE);
foreach $input (***@lines)
{
chomp($input);
if ($input =~ m/\w+/)
{
print ("$input\n");
}
}
2017/11/12
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Regular Expressions
Perl's Regular Expression Operators
Matching: m//.
This operator returns true if PATTERN is found in $_.
Ex: m/hello/
Substitution: s///.
This operator replaces the sub-string matched by
PATTERN with REPLACEMENT.
Ex: s/hello/HELLO/
translation. tr///.
This operator replaces characters specified by CHARACTERS with the characters in REPLACEMENTS.
Ex: tr/ab/c/
The Binding Operators (=~ and !~)
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Regular Expressions
Option
Description
g
This option finds all occurrences of the pattern in the string. A list of matches is returned or you can iterate over the matches using a loop statement.
i
This option ignores the case of characters in the string.
m
This option treats the string as multiple lines. Perl does some optimization by assuming that $_ contains a single line of input. If you know that it contains multiple newline characters, use this option to turn off the optimization.
o
This piles the pattern only once. You can achieve some small perf