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A few grammar and punctuation improvements
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@ -31,64 +31,65 @@
* [Tiếng Việt](translations/README-vn.md)
* [فارسی](translations/README-fa.md)
## What is Regular Expression?
## What are Regular Expressions?
> Regular expression is a group of characters or symbols which is used to find a specific pattern from a text.
> A regular expression is a group of characters or symbols which is used to find a specific pattern in a text.
A regular expression is a pattern that is matched against a subject string from
left to right. Regular expression is used for replacing a text within a string,
validating form, extract a substring from a string based upon a pattern match,
and so much more. The word "Regular expression" is a mouthful, so you will usually
find the term abbreviated as "regex" or "regexp".
left to right. Regular expressions are used to replace text within a string,
validating forms, extracting a substring from a string based on a pattern match,
and so much more. The term "regular expression" is a mouthful, so you will usually
find the term abbreviated to "regex" or "regexp".
Imagine you are writing an application and you want to set the rules for when a
user chooses their username. We want to allow the username to contain letters,
numbers, underscores and hyphens. We also want to limit the number of characters
in username so it does not look ugly. We use the following regular expression to
validate a username:
in the username so it does not look ugly. We can use the following regular expression to
validate the username:
<br/><br/>
<p align="center">
<img src="./img/regexp-en.png" alt="Regular expression">
</p>
Above regular expression can accept the strings `john_doe`, `jo-hn_doe` and
`john12_as`. It does not match `Jo` because that string contains uppercase
The regular expression above can accept the strings `john_doe`, `jo-hn_doe` and
`john12_as`. It does not match `Jo` because that string contains an uppercase
letter and also it is too short.
## Table of Contents
- [Basic Matchers](#1-basic-matchers)
- [Meta character](#2-meta-characters)
- [Full stop](#21-full-stop)
- [Character set](#22-character-set)
- [Negated character set](#221-negated-character-set)
- [Meta Characters](#2-meta-characters)
- [The Full Stop](#21-the-full-stops)
- [Character Sets](#22-character-sets)
- [Negated Character Sets](#221-negated-character-sets)
- [Repetitions](#23-repetitions)
- [The Star](#231-the-star)
- [The Plus](#232-the-plus)
- [The Question Mark](#233-the-question-mark)
- [Braces](#24-braces)
- [Character Group](#25-character-group)
- [Capturing Groups](#25-capturing-groups)
- [Non-Capturing Groups](#251-non-capturing-groups)
- [Alternation](#26-alternation)
- [Escaping special character](#27-escaping-special-character)
- [Escaping Special Characters](#27-escaping-special-characters)
- [Anchors](#28-anchors)
- [Caret](#281-caret)
- [Dollar](#282-dollar)
- [The Caret](#281-the-caret)
- [The Dollar Sign](#282-the-dollar-sign)
- [Shorthand Character Sets](#3-shorthand-character-sets)
- [Lookaround](#4-lookaround)
- [Lookarounds](#4-lookarounds)
- [Positive Lookahead](#41-positive-lookahead)
- [Negative Lookahead](#42-negative-lookahead)
- [Positive Lookbehind](#43-positive-lookbehind)
- [Negative Lookbehind](#44-negative-lookbehind)
- [Flags](#5-flags)
- [Case Insensitive](#51-case-insensitive)
- [Global search](#52-global-search)
- [Global Search](#52-global-search)
- [Multiline](#53-multiline)
- [Greedy vs lazy matching](#6-greedy-vs-lazy-matching)
- [Greedy vs Lazy Matching](#6-greedy-vs-lazy-matching)
## 1. Basic Matchers
A regular expression is just a pattern of characters that we use to perform
A regular expression is just a pattern of characters that we use to perform a
search in a text. For example, the regular expression `the` means: the letter
`t`, followed by the letter `h`, followed by the letter `e`.
@ -112,7 +113,7 @@ not match the string `the`.
## 2. Meta Characters
Meta characters are the building blocks of the regular expressions. Meta
Meta characters are the building blocks of regular expressions. Meta
characters do not stand for themselves but instead are interpreted in some
special way. Some meta characters have a special meaning and are written inside
square brackets. The meta characters are as follows:
@ -132,9 +133,9 @@ square brackets. The meta characters are as follows:
|^|Matches the beginning of the input.|
|$|Matches the end of the input.|
## 2.1 Full stop
## 2.1 The Full Stop
Full stop `.` is the simplest example of meta character. The meta character `.`
The full stop `.` is the simplest example of a meta character. The meta character `.`
matches any single character. It will not match return or newline characters.
For example, the regular expression `.ar` means: any character, followed by the
letter `a`, followed by the letter `r`.
@ -145,11 +146,11 @@ letter `a`, followed by the letter `r`.
[Test the regular expression](https://regex101.com/r/xc9GkU/1)
## 2.2 Character set
## 2.2 Character Sets
Character sets are also called character class. Square brackets are used to
Character sets are also called character classes. Square brackets are used to
specify character sets. Use a hyphen inside a character set to specify the
characters' range. The order of the character range inside square brackets
characters' range. The order of the character range inside the square brackets
doesn't matter. For example, the regular expression `[Tt]he` means: an uppercase
`T` or lowercase `t`, followed by the letter `h`, followed by the letter `e`.
@ -160,7 +161,7 @@ doesn't matter. For example, the regular expression `[Tt]he` means: an uppercase
[Test the regular expression](https://regex101.com/r/2ITLQ4/1)
A period inside a character set, however, means a literal period. The regular
expression `ar[.]` means: a lowercase character `a`, followed by letter `r`,
expression `ar[.]` means: a lowercase character `a`, followed by the letter `r`,
followed by a period `.` character.
<pre>
@ -169,7 +170,7 @@ followed by a period `.` character.
[Test the regular expression](https://regex101.com/r/wL3xtE/1)
### 2.2.1 Negated character set
### 2.2.1 Negated Character Sets
In general, the caret symbol represents the start of the string, but when it is
typed after the opening square bracket it negates the character set. For
@ -184,14 +185,14 @@ followed by the character `a`, followed by the letter `r`.
## 2.3 Repetitions
Following meta characters `+`, `*` or `?` are used to specify how many times a
The meta characters `+`, `*` or `?` are used to specify how many times a
subpattern can occur. These meta characters act differently in different
situations.
### 2.3.1 The Star
The symbol `*` matches zero or more repetitions of the preceding matcher. The
regular expression `a*` means: zero or more repetitions of preceding lowercase
The `*` symbol matches zero or more repetitions of the preceding matcher. The
regular expression `a*` means: zero or more repetitions of the preceding lowercase
character `a`. But if it appears after a character set or class then it finds
the repetitions of the whole character set. For example, the regular expression
`[a-z]*` means: any number of lowercase letters in a row.
@ -205,8 +206,8 @@ the repetitions of the whole character set. For example, the regular expression
The `*` symbol can be used with the meta character `.` to match any string of
characters `.*`. The `*` symbol can be used with the whitespace character `\s`
to match a string of whitespace characters. For example, the expression
`\s*cat\s*` means: zero or more spaces, followed by lowercase character `c`,
followed by lowercase character `a`, followed by lowercase character `t`,
`\s*cat\s*` means: zero or more spaces, followed by a lowercase `c`,
followed by a lowercase `a`, followed by a lowercase `t`,
followed by zero or more spaces.
<pre>
@ -217,10 +218,10 @@ followed by zero or more spaces.
### 2.3.2 The Plus
The symbol `+` matches one or more repetitions of the preceding character. For
example, the regular expression `c.+t` means: lowercase letter `c`, followed by
at least one character, followed by the lowercase character `t`. It needs to be
clarified that `t` is the last `t` in the sentence.
The `+` symbol matches one or more repetitions of the preceding character. For
example, the regular expression `c.+t` means: a lowercase `c`, followed by
at least one character, followed by a lowercase `t`. It needs to be
clarified that`t` is the last `t` in the sentence.
<pre>
"c.+t" => The fat <a href="#learn-regex"><strong>cat sat on the mat</strong></a>.
@ -230,11 +231,10 @@ clarified that `t` is the last `t` in the sentence.
### 2.3.3 The Question Mark
In regular expression the meta character `?` makes the preceding character
In regular expressions, the meta character `?` makes the preceding character
optional. This symbol matches zero or one instance of the preceding character.
For example, the regular expression `[T]?he` means: Optional the uppercase
letter `T`, followed by the lowercase character `h`, followed by the lowercase
character `e`.
For example, the regular expression `[T]?he` means: Optional uppercase
`T`, followed by a lowercase `h`, followed bya lowercase `e`.
<pre>
"[T]he" => <a href="#learn-regex"><strong>The</strong></a> car is parked in the garage.
@ -250,10 +250,10 @@ character `e`.
## 2.4 Braces
In regular expression braces that are also called quantifiers are used to
In regular expressions, braces (also called quantifiers) are used to
specify the number of times that a character or a group of characters can be
repeated. For example, the regular expression `[0-9]{2,3}` means: Match at least
2 digits but not more than 3 (characters in the range of 0 to 9).
2 digits, but not more than 3, ranging from 0 to 9.
<pre>
"[0-9]{2,3}" => The number was 9.<a href="#learn-regex"><strong>999</strong></a>7 but we rounded it off to <a href="#learn-regex"><strong>10</strong></a>.0.
@ -262,7 +262,7 @@ repeated. For example, the regular expression `[0-9]{2,3}` means: Match at least
[Test the regular expression](https://regex101.com/r/juM86s/1)
We can leave out the second number. For example, the regular expression
`[0-9]{2,}` means: Match 2 or more digits. If we also remove the comma the
`[0-9]{2,}` means: Match 2 or more digits. If we also remove the comma, the
regular expression `[0-9]{3}` means: Match exactly 3 digits.
<pre>
@ -277,16 +277,16 @@ regular expression `[0-9]{3}` means: Match exactly 3 digits.
[Test the regular expression](https://regex101.com/r/Sivu30/1)
## 2.5 Capturing Group
## 2.5 Capturing Groups
A capturing group is a group of sub-patterns that is written inside Parentheses
`(...)`. Like as we discussed before that in regular expression if we put a quantifier
after a character then it will repeat the preceding character. But if we put quantifier
A capturing group is a group of sub-patterns that is written inside parentheses
`(...)`. As discussed before, in regular expressions, if we put a quantifier
after a character then it will repeat the preceding character. But if we put a quantifier
after a capturing group then it repeats the whole capturing group. For example,
the regular expression `(ab)*` matches zero or more repetitions of the character
"ab". We can also use the alternation `|` meta character inside capturing group.
For example, the regular expression `(c|g|p)ar` means: lowercase character `c`,
`g` or `p`, followed by character `a`, followed by character `r`.
"ab". We can also use the alternation `|` meta character inside a capturing group.
For example, the regular expression `(c|g|p)ar` means: a lowercase `c`,
`g` or `p`, followed by `a`, followed by `r`.
<pre>
"(c|g|p)ar" => The <a href="#learn-regex"><strong>car</strong></a> is <a href="#learn-regex"><strong>par</strong></a>ked in the <a href="#learn-regex"><strong>gar</strong></a>age.
@ -294,15 +294,15 @@ For example, the regular expression `(c|g|p)ar` means: lowercase character `c`,
[Test the regular expression](https://regex101.com/r/tUxrBG/1)
Note that capturing groups do not only match but also capture the characters for use in
the parent language. The parent language could be python or javascript or virtually any
Note that capturing groups do not only match, but also capture, the characters for use in
the parent language. The parent language could be Python or JavaScript or virtually any
language that implements regular expressions in a function definition.
### 2.5.1 Non-capturing group
### 2.5.1 Non-Capturing Groups
A non-capturing group is a capturing group that only matches the characters, but
A non-capturing group is a capturing group that matches the characters but
does not capture the group. A non-capturing group is denoted by a `?` followed by a `:`
within parenthesis `(...)`. For example, the regular expression `(?:c|g|p)ar` is similar to
within parentheses `(...)`. For example, the regular expression `(?:c|g|p)ar` is similar to
`(c|g|p)ar` in that it matches the same characters but will not create a capture group.
<pre>
@ -319,13 +319,13 @@ See also [4. Lookaround](#4-lookaround).
In a regular expression, the vertical bar `|` is used to define alternation.
Alternation is like an OR statement between multiple expressions. Now, you may be
thinking that character set and alternation works the same way. But the big
difference between character set and alternation is that character set works on
character level but alternation works on expression level. For example, the
regular expression `(T|t)he|car` means: either (uppercase character `T` or lowercase
`t`, followed by lowercase character `h`, followed by lowercase character `e`) OR
(lowercase character `c`, followed by lowercase character `a`, followed by
lowercase character `r`). Note that I put the parentheses for clarity, to show that either expression
thinking that character sets and alternation work the same way. But the big
difference between character sets and alternation is that character sets work at the
character level but alternation works at the expression level. For example, the
regular expression `(T|t)he|car` means: either (an uppercase `T` or a lowercase
`t`, followed by a lowercase `h`, followed by a lowercase `e`) OR
(a lowercase `c`, followed by a lowercase `a`, followed by
a lowercase `r`). Note that I included the parentheses for clarity, to show that either expression
in parentheses can be met and it will match.
<pre>
@ -334,17 +334,15 @@ in parentheses can be met and it will match.
[Test the regular expression](https://regex101.com/r/fBXyX0/1)
## 2.7 Escaping special character
## 2.7 Escaping Special Characters
Backslash `\` is used in regular expression to escape the next character. This
allows us to specify a symbol as a matching character including reserved
characters `{ } [ ] / \ + * . $ ^ | ?`. To use a special character as a matching
character prepend `\` before it.
A backslash `\` is used in regular expressions to escape the next character. This
allows us to include reserved characters such as `{ } [ ] / \ + * . $ ^ | ?` as matching characters. To use one of these special character as a matching character, prepend it with `\`.
For example, the regular expression `.` is used to match any character except
newline. Now to match `.` in an input string the regular expression
`(f|c|m)at\.?` means: lowercase letter `f`, `c` or `m`, followed by lowercase
character `a`, followed by lowercase letter `t`, followed by optional `.`
For example, the regular expression `.` is used to match any character except a
newline. Now, to match `.` in an input string, the regular expression
`(f|c|m)at\.?` means: a lowercase `f`, `c` or `m`, followed by a lowercase
`a`, followed by a lowercase `t`, followed by an optional `.`
character.
<pre>
@ -357,20 +355,20 @@ character.
In regular expressions, we use anchors to check if the matching symbol is the
starting symbol or ending symbol of the input string. Anchors are of two types:
First type is Caret `^` that check if the matching character is the start
character of the input and the second type is Dollar `$` that checks if matching
The first type is the caret `^` that check if the matching character is the first
character of the input and the second type is the dollar sign `$` which checks if a matching
character is the last character of the input string.
### 2.8.1 Caret
### 2.8.1 The Caret
Caret `^` symbol is used to check if matching character is the first character
of the input string. If we apply the following regular expression `^a` (if a is
the starting symbol) to input string `abc` it matches `a`. But if we apply
regular expression `^b` on above input string it does not match anything.
Because in input string `abc` "b" is not the starting symbol. Let's take a look
at another regular expression `^(T|t)he` which means: uppercase character `T` or
lowercase character `t` is the start symbol of the input string, followed by
lowercase character `h`, followed by lowercase character `e`.
The caret symbol `^` is used to check if a matching character is the first character
of the input string. If we apply the following regular expression `^a` (meaning 'a' must be
the starting character) to the string `abc`, it will match `a`. But if we apply
the regular expression `^b` to the above string, it will not match anything.
Because in the string `abc`, the "b" is not the starting character. Let's take a look
at another regular expression `^(T|t)he` which means: an uppercase `T` or
a lowercase `t` must be the first character in the string, followed by a
lowercase `h`, followed by a lowercase `e`.
<pre>
"(T|t)he" => <a href="#learn-regex"><strong>The</strong></a> car is parked in <a href="#learn-regex"><strong>the</strong></a> garage.
@ -384,12 +382,12 @@ lowercase character `h`, followed by lowercase character `e`.
[Test the regular expression](https://regex101.com/r/jXrKne/1)
### 2.8.2 Dollar
### 2.8.2 The Dollar Sign
Dollar `$` symbol is used to check if matching character is the last character
of the input string. For example, regular expression `(at\.)$` means: a
lowercase character `a`, followed by lowercase character `t`, followed by a `.`
character and the matcher must be end of the string.
The dollar sign `$` is used to check if a matching character is the last character
in the string. For example, the regular expression `(at\.)$` means: a
lowercase `a`, followed by a lowercase `t`, followed by a `.`
character and the matcher must be at the end of the string.
<pre>
"(at\.)" => The fat c<a href="#learn-regex"><strong>at.</strong></a> s<a href="#learn-regex"><strong>at.</strong></a> on the m<a href="#learn-regex"><strong>at.</strong></a>
@ -405,30 +403,29 @@ character and the matcher must be end of the string.
## 3. Shorthand Character Sets
Regular expression provides shorthands for the commonly used character sets,
which offer convenient shorthands for commonly used regular expressions. The
shorthand character sets are as follows:
There are a number of convenient shorthands for commonly used character sets/
regular expressions:
|Shorthand|Description|
|:----:|----|
|.|Any character except new line|
|\w|Matches alphanumeric characters: `[a-zA-Z0-9_]`|
|\W|Matches non-alphanumeric characters: `[^\w]`|
|\d|Matches digit: `[0-9]`|
|\D|Matches non-digit: `[^\d]`|
|\s|Matches whitespace character: `[\t\n\f\r\p{Z}]`|
|\S|Matches non-whitespace character: `[^\s]`|
|\d|Matches digits: `[0-9]`|
|\D|Matches non-digits: `[^\d]`|
|\s|Matches whitespace characters: `[\t\n\f\r\p{Z}]`|
|\S|Matches non-whitespace characters: `[^\s]`|
## 4. Lookaround
## 4. Lookarounds
Lookbehind and lookahead (also called lookaround) are specific types of
***non-capturing groups*** (used to match the pattern but not included in matching
list). Lookarounds are used when we have the condition that this pattern is
preceded or followed by another certain pattern. For example, we want to get all
numbers that are preceded by `$` character from the following input string
`$4.44 and $10.88`. We will use following regular expression `(?<=\$)[0-9\.]*`
which means: get all the numbers which contain `.` character and are preceded
by `$` character. Following are the lookarounds that are used in regular
Lookbehinds and lookaheads (also called lookarounds) are specific types of
***non-capturing groups*** (used to match a pattern but without including it in the matching
list). Lookarounds are used when we a pattern must be
preceded or followed by another pattern. For example, imagine we want to get all
numbers that are preceded by the `$` character from the string
`$4.44 and $10.88`. We will use the following regular expression `(?<=\$)[0-9\.]*`
which means: get all the numbers which contain the `.` character and are preceded
by the `$` character. These are the lookarounds that are used in regular
expressions:
|Symbol|Description|
@ -444,12 +441,12 @@ The positive lookahead asserts that the first part of the expression must be
followed by the lookahead expression. The returned match only contains the text
that is matched by the first part of the expression. To define a positive
lookahead, parentheses are used. Within those parentheses, a question mark with
equal sign is used like this: `(?=...)`. Lookahead expression is written after
the equal sign inside parentheses. For example, the regular expression
`(T|t)he(?=\sfat)` means: optionally match lowercase letter `t` or uppercase
letter `T`, followed by letter `h`, followed by letter `e`. In parentheses we
define positive lookahead which tells regular expression engine to match `The`
or `the` which are followed by the word `fat`.
an equals sign is used like this: `(?=...)`. The lookahead expressions is written after
the equals sign inside parentheses. For example, the regular expression
`(T|t)he(?=\sfat)` means: match either a lowercase `t` or an uppercase
`T`, followed by the letter `h`, followed by the letter `e`. In parentheses we
define a positive lookahead which tells the regular expression engine to match `The`
or `the` only if it's followed by the word `fat`.
<pre>
"(T|t)he(?=\sfat)" => <a href="#learn-regex"><strong>The</strong></a> fat cat sat on the mat.
@ -459,13 +456,12 @@ or `the` which are followed by the word `fat`.
### 4.2 Negative Lookahead
Negative lookahead is used when we need to get all matches from input string
that are not followed by a pattern. Negative lookahead is defined same as we define
positive lookahead but the only difference is instead of equal `=` character we
use negation `!` character i.e. `(?!...)`. Let's take a look at the following
Negative lookaheads are used when we need to get all matches from an input string
that are not followed by a certain pattern. A negative lookahead is written the same way as a
positive lookahead. The only difference is, instead of an equals sign `=`, we
use an exclamation mark `!` to indicate negation i.e. `(?!...)`. Let's take a look at the following
regular expression `(T|t)he(?!\sfat)` which means: get all `The` or `the` words
from input string that are not followed by the word `fat` precedes by a space
character.
from the input string that are not followed by a space character and the word `fat`.
<pre>
"(T|t)he(?!\sfat)" => The fat cat sat on <a href="#learn-regex"><strong>the</strong></a> mat.
@ -475,10 +471,10 @@ character.
### 4.3 Positive Lookbehind
Positive lookbehind is used to get all the matches that are preceded by a
specific pattern. Positive lookbehind is denoted by `(?<=...)`. For example, the
Positive lookbehinds are used to get all the matches that are preceded by a
specific pattern. Positive lookbehinds are written `(?<=...)`. For example, the
regular expression `(?<=(T|t)he\s)(fat|mat)` means: get all `fat` or `mat` words
from input string that are after the word `The` or `the`.
from the input string that come after the word `The` or `the`.
<pre>
"(?<=(T|t)he\s)(fat|mat)" => The <a href="#learn-regex"><strong>fat</strong></a> cat sat on the <a href="#learn-regex"><strong>mat</strong></a>.
@ -488,9 +484,9 @@ from input string that are after the word `The` or `the`.
### 4.4 Negative Lookbehind
Negative lookbehind is used to get all the matches that are not preceded by a
specific pattern. Negative lookbehind is denoted by `(?<!...)`. For example, the
regular expression `(?<!(T|t)he\s)(cat)` means: get all `cat` words from input
Negative lookbehinds are used to get all the matches that are not preceded by a
specific pattern. Negative lookbehinds are written `(?<!...)`. For example, the
regular expression `(?<!(T|t)he\s)(cat)` means: get all `cat` words from the input
string that are not after the word `The` or `the`.
<pre>
@ -507,17 +503,17 @@ integral part of the RegExp.
|Flag|Description|
|:----:|----|
|i|Case insensitive: Sets matching to be case-insensitive.|
|g|Global Search: Search for a pattern throughout the input string.|
|m|Multiline: Anchor meta character works on each line.|
|i|Case insensitive: Match will be case-insensitive.|
|g|Global Search: Match all instances, not just the first.|
|m|Multiline: Anchor meta characters work on each line.|
### 5.1 Case Insensitive
The `i` modifier is used to perform case-insensitive matching. For example, the
regular expression `/The/gi` means: uppercase letter `T`, followed by lowercase
character `h`, followed by character `e`. And at the end of regular expression
regular expression `/The/gi` means: an uppercase `T`, followed by a lowercase
`h`, followed by an `e`. And at the end of regular expression
the `i` flag tells the regular expression engine to ignore the case. As you can
see we also provided `g` flag because we want to search for the pattern in the
see, we also provided `g` flag because we want to search for the pattern in the
whole input string.
<pre>
@ -532,13 +528,13 @@ whole input string.
[Test the regular expression](https://regex101.com/r/ahfiuh/1)
### 5.2 Global search
### 5.2 Global Search
The `g` modifier is used to perform a global match (find all matches rather than
The `g` modifier is used to perform a global match (finds all matches rather than
stopping after the first match). For example, the regular expression`/.(at)/g`
means: any character except new line, followed by lowercase character `a`,
followed by lowercase character `t`. Because we provided `g` flag at the end of
the regular expression now it will find all matches in the input string, not just the first one (which is the default behavior).
means: any character except a new line, followed by a lowercase `a`,
followed by a lowercase `t`. Because we provided the `g` flag at the end of
the regular expression, it will now find all matches in the input string, not just the first one (which is the default behavior).
<pre>
"/.(at)/" => The <a href="#learn-regex"><strong>fat</strong></a> cat sat on the mat.
@ -554,12 +550,12 @@ the regular expression now it will find all matches in the input string, not jus
### 5.3 Multiline
The `m` modifier is used to perform a multi-line match. As we discussed earlier
anchors `(^, $)` are used to check if pattern is the beginning of the input or
end of the input string. But if we want that anchors works on each line we use
`m` flag. For example, the regular expression `/at(.)?$/gm` means: lowercase
character `a`, followed by lowercase character `t`, optionally anything except
new line. And because of `m` flag now regular expression engine matches pattern
The `m` modifier is used to perform a multi-line match. As we discussed earlier,
anchors `(^, $)` are used to check if a pattern is at the beginning of the input or
the end. But if we want the anchors to work on each line, we use
the `m` flag. For example, the regular expression `/at(.)?$/gm` means: a lowercase
`a`, followed by a lowercase `t` and, optionally, anything except
a new line. And because of the `m` flag, the regular expression engine now matches patterns
at the end of each line in a string.
<pre>
@ -578,9 +574,9 @@ at the end of each line in a string.
[Test the regular expression](https://regex101.com/r/E88WE2/1)
## 6. Greedy vs lazy matching
By default regex will do greedy matching which means it will match as long as
possible. We can use `?` to match in lazy way which means as short as possible.
## 6. Greedy vs Lazy Matching
By default, a regex will perform a greedy match, which means the match will be as long as
possible. We can use `?` to match in a lazy way, which means the match should be as short as possible.
<pre>
"/(.*at)/" => <a href="#learn-regex"><strong>The fat cat sat on the mat</strong></a>. </pre>
@ -597,7 +593,7 @@ possible. We can use `?` to match in lazy way which means as short as possible.
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