Regular Expression Basics - 1

In this post I wanna share some basic regular expression rules. But first I need to write down the metacharacters. Metacharacters are those characters which have a special meaning in regular expressions. i.e. "-" and "[" handled differently in regular expressions. Metacharcters are are as follows:

 

[  {  (  )  \  ^  $  .  |  ?  *  +

/1.5/g
Dot (.) matches anything, except for the line breaks.

1a5, 41e5y, 1x5o, 89xy1&5P55 are all the same

****

If you need to include dot (.) in your search than you have to put a backslash (\) before the dot (.)
/3\.9/g

According to the above expression it matches only the characters "3" and "9" in between they have a "."
 

93.96, a3.9t, 13.9s, x3.9t

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If you want to search more characters which you don't want to type one-by-one than there is a solution which is called quantifiers.

For example if you want to search 10 "b"s than you have to type either /bbbbbbbbbb/g or /b{10}/g. If you're gonna search 10 "b"s than that's may be okay but if you're gonna search 100 "b"s it doesn't seem so straightforward.

If you want to search at least 6 "b"s than you have to put a comma (,) after the number which is between paranthesis. /b{6,}/g won't catch 5 "b"s it will only catch "b"s which are 6 or more.

If you want at least 7 "b"s but at most 10 "b"s then you have to type two numbers in between the paranthesis. i.e. /b{7,10}/g

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/[gyb]/g

This regexp matches either "g", or "y" or "b". This regexp finds only "1" occurence of one of these letters.

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/[gyb]+/g

If you put a "+" after the square bracket then it will find any occurences of "g" or "y" or "b".
 

ggyybb, gyyyybbb, bbb, yy, bgyyy, yyggaaa, lkbgyata, 12hytbyggg90g0b

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/[a-z]+/g

If you want to catch all the letters of the English alphabet in the regexp than you can define a range. The regular expression above catches every letter of the English alphabet. But it doesn't catch any numbers or symbols regardless of their occurences.
 

abjuyr, amnxc5, 77yhbbd76dg76, xbn8dmmdn, %!98hnsb!!mmcasd98lk=

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/[a-z0-9]+/g

The expression above detects all the letters of the English alphabet and all the letters regardless of their occurences.

11009hsndh%88uj, 56+67=123=xyz, $var=99

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/[a-zA-Z0-9_]+/g equals to /\w+/g

There are some shortcuts of the whole English alphabet and whole numbers. i.e. the regular expressions /[a-z0-9_]+/g and /\w+/g are the same. Both find the letters (small or capital) and numbers including the underscore (_) regardless of their occurences.

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/[0-9]+/g equals to /\d+/g

If you want to match only numbers then you have to use the one of the above regular expressions.

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/^[m-z]+/g
You can negate the classes with the "^" character. With the above regular expression you will catch the characters other than [t-z]. namely the regular expressin will match the small letters a, b, c, d, e, f, g, h, i, j, k, l and all the capital letters from A to Z and also the numbers 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 and also symbols like %, & etc.

whatta99yathink88? iaint77do21ANYTHING%% HappyNewYear-In-2017!!!

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/^\w+/g = /\W+/g
The above regualar expression above matches anything that's not the letter or number or underscore (_)

Mr.&MrsBrown_werein1960!s

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/^\d+/g = /\D+/g

The above regular expression above matches anything that is not a number.

14mfly1ngt0C4n4ry15l4nd 4w0rldw1th0utr3g3xp5??!!