May 2009
Intermediate to advanced
510 pages
15h
English
Content preview from Regular Expressions Cookbook
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2.5. Match Something at the Start and/or the End of a Line
Problem
Create four regular expressions. Match the word alpha, but only if it occurs at the very
beginning of the subject text. Match the word omega, but only if it
occurs at the very end of the subject text. Match the word begin, but only if it
occurs at the beginning of a line. Match the word end, but only if it
occurs at the end of a line.
Solution
Start of the subject
^alpha
| Regex options: None (“^ and $ match at line breaks” must not be set) |
| Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python |
\Aalpha
| Regex options: None |
| Regex flavors: .NET, Java, PCRE, Perl, Python, Ruby |
End of the subject
omega$
| Regex options: None (“^ and $ match at line breaks” must not be set) |
| Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python |
omega\Z
| Regex options: None |
| Regex flavors: .NET, Java, PCRE, Perl, Python, Ruby |
Start of a line
^begin
| Regex options: ^ and $ match at line breaks |
| Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
End of a line
end$
| Regex options: ^ and $ match at line breaks |
| Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
Discussion
Anchors and lines
The regular expression tokens ‹^›, ‹$›, ‹\A›, ‹\Z›, and ‹\z› are called anchors.
They do not match any characters. Instead, they match
at certain positions, effectively anchoring the regular expression
match at those positions.
A line is the part of the subject text that lies between the start of the subject and a line break, between two line breaks, or between ...
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.