Example General Resource Tools

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Escape sequence - Tab character \t
What is the escape sequence for the Tab character? How to write a regular expression to captures tab delimited fields like this: Milk $0.99 No tax ? The escape sequence for the Tag character is \t, which is the same as \x09. The regular expression to capture tab delimited fields is: ([^\t]*+)\t? [^\... 2013-01-26, 3830👍, 0💬

1 or 0 times repetition quantifier ?
What is the 1 or 0 times repetition quantifier? How to use it? How to write a regular expression using a 1 or 0 times repetition quantifier to capture both spellings of skilful and skillful ? The "1 or 0 times" repetition quantifier allows us to create a special logical OR operation of "match the pa... 2013-01-26, 2745👍, 0💬

1 or more times repetition quantifier +
What is the 1 or more times repetition quantifier? How to use it? How to write a regular expression using a repetition quantifier to capture all words in a PHP script code like this: function get($key) {if (array_key_exists($key,$_POST) )return $_POST[$key]; else return "";} ? --- Answer The "1 or m... 2013-01-26, 2768👍, 0💬

0 or more times repetition quantifier *
What is the 0 or more times repetition quantifier? How to use it? How to write a regular expression using a repetition quantifier to capture all names and values in a URL query string like this: User=Jack&Age=&City=Pa ris? The "0 or more times" repetition quantifier allows us to repeat a pat... 2013-01-26, 2907👍, 0💬

Exact n times repetition quantifier {n}
What is the exact n times repetition quantifier? How to use it? How to write a regular expression using a repetition quantifier to capture Visa card numbers that have 16 digits like this: 4111111111111111 ? The "exact n times" repetition quantifier allows us to repeat a pattern unit exactly n times ... 2013-01-26, 2799👍, 0💬

Limited number of repetitions quantifier {n,m}
What is the limited number of repetitions quantifier? How to use it? How to write a regular expression using a repetition quantifier to ensure my password is between 8 and 12 characters long like this one: 9EA979114C ? The "limited number of repetitions" quantifier allows us to repeat a pattern unit... 2013-01-26, 2769👍, 0💬

n or more times repetition quantifier {n,}
What is the "n or more times" repetition quantifier? How to use it? How to write a regular expression using a repetition quantifier to capture the value of PI like: 3.1415926535897932384626433832 795028841971with a precision of at least 5 decimal digits? The "n or more times" repetition quantifier a... 2013-01-26, 2854👍, 0💬

Backtracking of quantified subpatterns
What is backtracking of quantified subpatterns? What does it mean that a quantified subpattern is "backtracked"? How to show that a quantified subpattern is "backtracked" on this PHP script: if ($t=10): echo "Just started...!"; endif; if ($t=11): echo "Hungry!"; endif; if ($t=12): echo ""Ah, lunch-t... 2013-01-26, 2737👍, 0💬

Possessive (non-backtracking) quantified subpatterns ++ *+ {}+
What is possessive (non-backtracking) quantified subpatterns? How to write a possessive quantified subpattern to match double-quoted strings like this: "He said: \“Hello!\”" ? If you don't want the default backtracking behavior of quantified subpatterns, you can turn it off by adding the "poss... 2013-01-26, 2868👍, 0💬

"non-greedy" on quantified subpatterns +? *? {}?
How turn off the the greediness of quantified subpatterns? I want the quantified subpattern to be matched the minimum number of times possible? How to create a "non-greedy" quantified subpattern on this PHP script: if ($t=10): echo "Just started...!"; endif; if ($t=11): echo "Hungry!"; endif; if ($t... 2013-01-26, 3583👍, 0💬

Greediness of quantified subpatterns
What is the greediness of quantified subpatterns? What does it mean that a quantified subpattern is "greedy"? How to show that a quantified subpattern is "greedy" on this PHP script: if ($t=10): echo "Just started...!"; endif; if ($t=11): echo "Hungry!"; endif; if ($t=12): echo ""Ah, lunch-time!"; e... 2013-01-26, 2775👍, 0💬

End of string anchor $
What is the "end of string" anchor in a regular expression? How to use it? How to write a regular expression using "end of string" anchor to validate words ending in 'z': quartz ? The "end of string" anchor is an atomic zero-width assertion specifing that the match must occur at the end of the strin... 2013-01-26, 2878👍, 0💬

Start of string anchor ^
What is the "start of string" anchor in a regular expression? How to use it? How to write a regular expression using "start of string" anchor to validate discover credit card numbers like: 6011963280099774 ? The "start of string" anchor is an atomic zero-width assertion specifing that the match must... 2013-01-26, 2751👍, 0💬

Backreferences \g1, \g2, ...
What is a backreference? How to use a backreference? How to write a regular expression using a backreferences to capture 5-letter reversible words in a text string like this: civic, level, radar, rotor or stats ? Backreferences are references representing catured sub strings already matched in earli... 2013-01-23, 5449👍, 0💬

Pattern groups (...)
What is pattern group? What are pattern groups used for? How to write a regular expression using groups to capture character names from the Ed, Edd 'n' Eddy animated comedy television series? The grouping mechanism allows a part of a regex to be treated as a single unit. A group is represented by re... 2013-01-23, 2815👍, 0💬

Negated word character class - \W
What is abbreviation of a negated character class of all word characters? Does it represents any characters except alphanumeric plus '_' characters? How to write a regular expression using a character class abbreviation to capture all sequences of non word characters in a PHP script code like this: ... 2013-01-23, 3603👍, 0💬

Word character class - \w
What is abbreviation of a character class of all word characters? Does it represents any alphanumeric plus '_' characters? How to write a regular expression using a character class abbreviation to capture all words in a PHP script code like this: function get($key) {if (array_key_exists($key,$_POST) ... 2013-01-23, 4232👍, 0💬

Negated white space character class - \S
What is abbreviation of a negated character class of all white space ASCII characters? Does it represents any characters except white space characters? How to write a regular expression using a character class abbreviation to capture tokens separated by white space characters in a text string like t... 2013-01-23, 3687👍, 0💬

White space character class - \s
What is abbreviation of a character class of all white space ASCII characters? How to write a regular expression using a character class abbreviation to capture all white space characters in a text string like this: Name: Jack; Age: 25; City: Paris ? The predefined abbreviation of a character class ... 2013-01-23, 3790👍, 0💬

Negated decimal digit character class - \D
What is abbreviation of a negated character class of all decimal digits? Does it represents any characters except decimal digits? How to write a regular expression using a character class abbreviation to capture letters from a Canadian postal code string: L3R 9Z7 ? The predefined abbreviation of a n... 2013-01-23, 3710👍, 0💬

Decimal digit character class - \d
What is abbreviation of a character class of all decimal digits? How to write a regular expression using a character class abbreviation to capture signed integer numbers in a text string like this: from -32768 to 32767 ? The predefined abbreviation of a character class of all decimal digits is \d, w... 2013-01-23, 3944👍, 0💬

Using character range in a character classe [a-z]
What is a character range in a character class? How to specify a character range in a character class in a regular expression? I have a string of hexadecimal digits, 46594963656E7465722E636F6D and want to use character ranges in a character class to validate it. A character range defines a set of po... 2013-01-22, 2996👍, 0💬

Logical OR (Alternation) operation (a|b)
What is a logical OR operation? How to specify a logical OR operation in a regular expression? How to use logical OR operations to build a regular expression to search and count common spamming terms from this email paragraph: I am inviting you for a business deal where this money will be shared bet... 2013-01-22, 2937👍, 0💬

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Example General Resource Tools