Updated: 2016-02-05-Fri 04:13:21 UTC

Perl Regex Examples:

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The Digits class (\d): Note: The digits class includes 0-9; however, it also includes the digits of other numeral systems for Unicode-configured sysetms (e.g., the chinese numerals: 一,二,三, etc.). The non-digits class is the compliment to the digits class (everything in the configured character set except digits).
#	REGEX Pattern:	Bound String that is tested... $`="" $&="" &'=""
01.	/\d/	"3" $`="" $&="3" &'=""
02.	/\d/	"34" $`="" $&="3" &'="4"
03.	/\d/	"-42" $`="-" $&="4" &'="2"
04.	/\d/	"-.14" $`="-." $&="1" &'="4"
05.	/\d./	"-3.14" $`="-" $&="3." &'="14"
06.	/^\d/	"-3.14" $`=undef $&=undef &'=undef Note: Match FAILED (match variables are undefined).
07.	/\d\d/	"-3.14" $`="-3." $&="14" &'=""
08.	/.\d/	"-3.14" $`="" $&="-3" &'=".14"
09.	/\d\d./	"-3.14" $`=undef $&=undef &'=undef Note: Match FAILED (match variables are undefined).
10.	/\d\d.?/	"-3.14" $`="-3." $&="14" &'=""
11.	/\d*/	"-3.14" $`="" $&="" &'="-3.14" Note: evaluation engine does not find a match at the first character '-', so it simply accepts a match of 0 digits. This might seem contrary to to the notion of greediness (i.e., you'd assume it would match at least one digit further down the string, but it likely doesn't because this would just be more runtime (and why waste time when it can match 0).
12.	/\d\d*/	"-3.14" $`="-" $&="3" &'=".14" Note: evaluation engine does not find a match at the first character '-', so it moves on and matches the first digit on the '3', then for the second digit, it simply accepts a match of 0 digits. This might seem contrary to the notion of greediness (i.e., you might wonder if it would try for a 'better' match at '14', but it likely doesn't because this would just be more runtime (and why waste time when it can match 0 digits for the second digit (\d*).
13.	/\d\d?/	"-3.14" $`="-" $&="3" &'=".14" Note: See previous example for similar grounds as to why it might not match where you might expect it to later in the string.
14.	/\d+/	"-3.14" $`="-" $&="3" &'=".14"
15.	/\d\d\|\d/	"-3.14" $`="-" $&="3" &'=".14"
16.	/\d\|\d\d/	"-3.14" $`="-" $&="3" &'=".14"
17.	/\D/	"-3.14" $`="" $&="-" &'="3.14"
18.	/\D\D/	"-3.14" $`=undef $&=undef &'=undef Note: Match FAILED (match variables are undefined).
19.	/\D\D?/	"-3.14" $`="" $&="-" &'="3.14"
20.	/\D\d/	"-3.14" $`="" $&="-3" &'=".14"
21.	/\d\D/	"-3.14" $`="-" $&="3." &'="14"
22.	/\d\d\D/	"-3.14" $`=undef $&=undef &'=undef Note: Match FAILED (match variables are undefined).
23.	/(\d\d\D)?/	"-3.14" $`="" $&="" &'="-3.14"
24.	/\d\d?\D/	"-3.14" $`="-" $&="3." &'="14"
25.	/(\d\d)?\D/	"-3.14" $`="" $&="-" &'="3.14"
26.	/^\d\D/	"-3.14" $`=undef $&=undef &'=undef Note: Match FAILED (match variables are undefined).
27.	/\D$/	"-3.14" $`=undef $&=undef &'=undef Note: Match FAILED (match variables are undefined).

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The Word class (\w): Note: TODO
#	REGEX Pattern:	Bound String that is tested... $`="" $&="" &'=""
01.	/\w/	"-3.14" $`="-" $&="3" &'=".14"
02.	/\w+/	"-3.14" $`="-" $&="3" &'=".14"
03.	/\w*/	"-3.14" $`="" $&="" &'="-3.14"
04.	/\w\w*/	"-3.14" $`="-" $&="3" &'=".14"
05.	/\w*\w/	"-3.14" $`="-" $&="3" &'=".14"
06.	/\w+\w/	"-3.14" $`="-3." $&="14" &'=""
07.	/\w+\d/	"-3.14" $`="-3." $&="14" &'=""
08.	/\d\w/	"-3.14" $`="-3." $&="14" &'=""
09.	/\w\D/	"-3.14" $`="-" $&="3." &'="14"

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The word bounday and non-word boundary classes (\b & \B): Note:
#	REGEX Pattern:	Bound String that is tested... $`="" $&="" &'=""
01.	/show\b/	"It is full of Python heritage that shall never wither in time; therefore, 'At Last the 1948 Show' is one of my favorite shows." $`=undef $&=undef &'=undef Note: Match FAILED (match variables are undefined).
02.	/\sshow/	"It is full of Python heritage that shall never wither in time; therefore, 'At Last the 1948 Show' is one of my favorite shows." $`="It is full of Python heritage that shall never wither in time; therefore, 'At Last the 1948 Show' is one of my favorite" $&=" show" &'="s."
03.	/\b\d{4}/	"It is full of Python heritage that shall never wither in time; therefore, 'At Last the 1948 Show' is one of my favorite shows." $`="It is full of Python heritage that shall never wither in time; therefore, 'At Last the " $&="1948" &'=" Show' is one of my favorite shows."
04.	/\b\d{4}\b/	"It is full of Python heritage that shall never wither in time; therefore, 'At Last the 1948 Show' is one of my favorite shows." $`="It is full of Python heritage that shall never wither in time; therefore, 'At Last the " $&="1948" &'=" Show' is one of my favorite shows."
05.	/\b\d.*/	"It is full of Python heritage that shall never wither in time; therefore, 'At Last the 1948 Show' is one of my favorite shows." $`="It is full of Python heritage that shall never wither in time; therefore, 'At Last the " $&="1948 Show' is one of my favorite shows." &'=""
06.	/\B\d.*/	"It is full of Python heritage that shall never wither in time; therefore, 'At Last the 1948 Show' is one of my favorite shows." $`="It is full of Python heritage that shall never wither in time; therefore, 'At Last the 1" $&="948 Show' is one of my favorite shows." &'=""
07.	/\b\d.*\b/	"It is full of Python heritage that shall never wither in time; therefore, 'At Last the 1948 Show' is one of my favorite shows." $`="It is full of Python heritage that shall never wither in time; therefore, 'At Last the " $&="1948 Show' is one of my favorite shows" &'="."
08.	/\s\d\b/	"It is full of Python heritage that shall never wither in time; therefore, 'At Last the 1948 Show' is one of my favorite shows." $`=undef $&=undef &'=undef Note: Match FAILED (match variables are undefined).
09.	/\s\w+\b/	"It is full of Python heritage that shall never wither in time; therefore, 'At Last the 1948 Show' is one of my favorite shows." $`="It" $&=" is" &'=" full of Python heritage that shall never wither in time; therefore, 'At Last the 1948 Show' is one of my favorite shows."
10.	/\b\d*\b/	"It is full of Python heritage that shall never wither in time; therefore, 'At Last the 1948 Show' is one of my favorite shows." $`="" $&="" &'="It is full of Python heritage that shall never wither in time; therefore, 'At Last the 1948 Show' is one of my favorite shows."
11.	/\b\d+\b/	"It is full of Python heritage that shall never wither in time; therefore, 'At Last the 1948 Show' is one of my favorite shows." $`="It is full of Python heritage that shall never wither in time; therefore, 'At Last the " $&="1948" &'=" Show' is one of my favorite shows."
12.	/\b\w*\b/	"It is full of Python heritage that shall never wither in time; therefore, 'At Last the 1948 Show' is one of my favorite shows." $`="" $&="It" &'=" is full of Python heritage that shall never wither in time; therefore, 'At Last the 1948 Show' is one of my favorite shows."
13.	/\b\w+\d+\b/	"It is full of Python heritage that shall never wither in time; therefore, 'At Last the 1948 Show' is one of my favorite shows." $`="It is full of Python heritage that shall never wither in time; therefore, 'At Last the " $&="1948" &'=" Show' is one of my favorite shows."
14.	/\b\w\d\d\w*\b/	"It is full of Python heritage that shall never wither in time; therefore, 'At Last the 1948 Show' is one of my favorite shows." $`="It is full of Python heritage that shall never wither in time; therefore, 'At Last the " $&="1948" &'=" Show' is one of my favorite shows."
15.	/\bhow\b/	"It is full of Python heritage that shall never wither in time; therefore, 'At Last the 1948 Show' is one of my favorite shows." $`=undef $&=undef &'=undef Note: Match FAILED (match variables are undefined).
16.	/\bshow\b/	"It is full of Python heritage that shall never wither in time; therefore, 'At Last the 1948 Show' is one of my favorite shows." $`="" $&="" &'="" Note: Match FAILED (match variables are undefined).
17.	/\bshow/	"It is full of Python heritage that shall never wither in time; therefore, 'At Last the 1948 Show' is one of my favorite shows." $`="It is full of Python heritage that shall never wither in time; therefore, 'At Last the 1948 Show' is one of my favorite " $&="show" &'="s."
18.	/show\b/	"It is full of Python heritage that shall never wither in time; therefore, 'At Last the 1948 Show' is one of my favorite shows." $`="" $&="" &'="" Note: Match FAILED (match variables are undefined).
19.	/\bthe\b/	"It is full of Python heritage that shall never wither in time; therefore, 'At Last the 1948 Show' is one of my favorite shows." $`="It is full of Python heritage that shall never wither in time; therefore, 'At Last " $&="the" &'=" 1948 Show' is one of my favorite shows."
20.	/the\b/	"It is full of Python heritage that shall never wither in time; therefore, 'At Last the 1948 Show' is one of my favorite shows." $`="It is full of Python heritage that shall never wither in time; therefore, 'At Last " $&="the" &'=" 1948 Show' is one of my favorite shows."
21.	/\bthe/	"It is full of Python heritage that shall never wither in time; therefore, 'At Last the 1948 Show' is one of my favorite shows." $`="It is full of Python heritage that shall never wither in time; " $&="the" &'="refore, 'At Last the 1948 Show' is one of my favorite shows."

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