Regex: What does the ^ do? What is it called?

[Al Cholic]

Hello,

Im trying to understand what the ^ and $ characters do when used in
regular expressions.

For example:

/^abc/ =~ "!abc"
returns nil
"You can use an anchor to match the beginning of a string"


/abc$/ =~ "abc!"
returns nil
"You can use an anchor to match the end of a string"


Why do these two statements return nil and how does the "anchor" work
exactly?

Can someone please clarify?


Does this mean that the regex is checking before the C\d+ ?
if @refdes[0] =~ /^C\d+/
return "Capacitor"

Thanks in advance.

 

[Thomas Wieczorek]

Hi

/^abc/ =~ "!abc"
returns nil
"You can use an anchor to match the beginning of a string"

Just like the definition says ^ is used to mark the beginning of a string:
/^abc/ =~ "abc!"
will return 0(the start of your pattern)

/abc$/ =~ "abc!"
returns nil
"You can use an anchor to match the end of a string"

$ is used to mark the end of a string:
/abc$/ =~ "!abc"
will return 0 again.

/^I love Ruby$/ will only match the string "I love Ruby" and not "He
said: I love Ruby". /I love Ruby/ or /I love Ruby/$ will match /^I
love Ruby$/

 

[Corey Jewett]

Hi


Just like the definition says ^ is used to mark the beginning of a
string:
/^abc/ =~ "abc!"
will return 0(the start of your pattern)



$ is used to mark the end of a string:
/abc$/ =~ "!abc"
will return 0 again.

/^I love Ruby$/ will only match the string "I love Ruby" and not "He
said: I love Ruby". /I love Ruby/ or /I love Ruby/$ will match /^I
love Ruby$/

^, $, \A, \Z, \B, etc. are called anchors.

Corey

 

[Al Cholic]

Thank you very much guys. This topic is much clearer now.

 

[Bertram Scharpf]

Hi,

Am Freitag, 06. Jul 2007, 14:33:12 +0900 schrieb Thomas Wieczorek:

Just like the definition says ^ is used to mark the beginning of a string:
/^abc/ =~ "abc!"

Another time:

^ and $ match the beginning/end of a ___line___
\A and \z match the beginning/end of a ___string___

This makes a difference when you string contains newline
characters.

"abc\nde\nfgh\n".scan /^./ # => ["a", "d", "f"]
"abc\nde\nfgh\n" =~ /.$/ # => 2
$& # => "c"

I would have guessed that /\z/ is faster than /$/ but /$/ is
approximately 10 times faster here. Does anybody know why?

Bertram

 

[Robert Dober]

/^abc/ =~ "abc!"
will return 0(the start of your pattern)



$ is used to mark the end of a string:
/abc$/ =~ "!abc"
will return 0 again.

A *very large* value of 0 that is

Robert

 

[Thomas Wieczorek]

A *very large* value of 0 that is

Ooops, should be 1. Sorry

 

[Lloyd Linklater]

Also, if the thread's title has meaning, a "^" is called a caret.

 

[Lloyd Linklater]

Dear Sir,

<<stuff here>>

THANKS FOR YOUR CO- OPERATIONS.
BEST REGARDS
SOULEYMANE TOUKARA
reply via this email: (e-mail address removed)

It seems that we were spammed with a classic internet con. How do we
get this junk removed?

 

[Jim Clark]

Thank you very much guys. This topic is much clearer now.

To learn more, a book I highly recommend is "Mastering Regular
Expressions" by Jeffrey Friedl.. Although the examples are written in
Perl (at least the first edition copy that I have), translating any of
these to Ruby should prove to be trivial. The time you spend reading the
book will save you many hours when you need to create, debug and/or
optimize more complex expressions.

Regards,
Jim

 

[John Joyce]

To learn more, a book I highly recommend is "Mastering Regular
Expressions" by Jeffrey Friedl.. Although the examples are written
in Perl (at least the first edition copy that I have), translating
any of these to Ruby should prove to be trivial. The time you spend
reading the book will save you many hours when you need to create,
debug and/or optimize more complex expressions.

Regards,
Jim

I second that book, I read some of it years ago, and it is
fascinating stuff!
Works well as a cookbook for regex's!