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bueltge committed Apr 20, 2020
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Expand Up @@ -46,7 +46,7 @@ Der abgebildete reguläre Ausdruck erlaubt bspw. folgende Eingaben `john_doe`, `
- [Basis Vergleiche](#1-basic-matchers)
- [Sonderzeichen](#2-meta-characters)
- [Punkt](#21-full-stop)
- [Character set](#22-character-set)
- [Zeichensätze](#22-zeichensaetze)
- [Invertierter Zeichensatz](#221-negated-character-set)
- [Wiederholungen](#23-repetitions)
- [Stern *](#231-the-star)
Expand Down Expand Up @@ -111,29 +111,21 @@ Sonderzeichen sind Bausteine von regulären Ausdrücken. Sonderzeichen stehen ni
## 2.1 Punkt

Der Punkt `.` ist die einfachste Möglichkeit von Sonderzeichen. Das Sonderzeichen `.`
entspricht jedem einzelnen Zeichen. 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`.
entspricht jedem einzelnen Zeichen. Es wird kein Zeilenumbruch oder Enter-Zeichen gefunden. Als Beispiel, der reguläre Ausdruck `.ar` bedeutet: ein beliebiges Zeichen, gefolgt von dem Buchstaben `a`, gefolgt vom Buchstaben `r`.

<pre>
".ar" => The <a href="#learn-regex"><strong>car</strong></a> <a href="#learn-regex"><strong>par</strong></a>ked in the <a href="#learn-regex"><strong>gar</strong></a>age.
</pre>
[Teste den regulären Ausdruck](https://regex101.com/r/xc9GkU/1)

[Test the regular expression](https://regex101.com/r/xc9GkU/1)
## 2.2 Zeichensätze

## 2.2 Character set

Character sets are also called character class. 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
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`.
Zeichensätze werden auch als Zeichenklasse bezeichnet. Zeichensätze werden in eckige Klammern angegeben. Um den Bereich der Zeichen anzugeben ist ein Bindestrich zu verwenden. Die Reihenfolge des Bereiches in den eckigen Klammern spielt keine Rolle. Zum Beispiel bedeutet der reguläre Ausdruck `[Tt]he`: ein groß geschriebenes `T` oder ein kleingeschriebenes `t`, gefolgt vom Buchstaben `h` und weiter gefolgt vom Buchstaben `e`.

<pre>
"[Tt]he" => <a href="#learn-regex"><strong>The</strong></a> car parked in <a href="#learn-regex"><strong>the</strong></a> garage.
</pre>

[Test the regular expression](https://regex101.com/r/2ITLQ4/1)
[Teste den regulären Ausdruck](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`,
Expand All @@ -143,20 +135,20 @@ followed by a period `.` character.
"ar[.]" => A garage is a good place to park a c<a href="#learn-regex"><strong>ar.</strong></a>
</pre>

[Test the regular expression](https://regex101.com/r/wL3xtE/1)
[Teste den regulären Ausdruck](https://regex101.com/r/wL3xtE/1)

### 2.2.1 Negated character set

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
example, the regular expression `[^c]ar` means: any character except `c`,
example, der reguläre Ausdruck `[^c]ar` means: any character except `c`,
followed by the character `a`, followed by the letter `r`.

<pre>
"[^c]ar" => The car <a href="#learn-regex"><strong>par</strong></a>ked in the <a href="#learn-regex"><strong>gar</strong></a>age.
</pre>

[Test the regular expression](https://regex101.com/r/nNNlq3/1)
[Teste den regulären Ausdruck](https://regex101.com/r/nNNlq3/1)

## 2.3 Repetitions

Expand All @@ -169,14 +161,14 @@ situations.
The symbol `*` matches zero or more repetitions of the preceding matcher. The
regular expression `a*` means: zero or more repetitions of 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
the repetitions of the whole character set. For example, der reguläre Ausdruck
`[a-z]*` means: any number of lowercase letters in a row.

<pre>
"[a-z]*" => T<a href="#learn-regex"><strong>he</strong></a> <a href="#learn-regex"><strong>car</strong></a> <a href="#learn-regex"><strong>parked</strong></a> <a href="#learn-regex"><strong>in</strong></a> <a href="#learn-regex"><strong>the</strong></a> <a href="#learn-regex"><strong>garage</strong></a> #21.
</pre>

[Test the regular expression](https://regex101.com/r/7m8me5/1)
[Teste den regulären Ausdruck](https://regex101.com/r/7m8me5/1)

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`
Expand All @@ -189,86 +181,86 @@ followed by zero or more spaces.
"\s*cat\s*" => The fat<a href="#learn-regex"><strong> cat </strong></a>sat on the con<a href="#learn-regex"><strong>cat</strong></a>enation.
</pre>

[Test the regular expression](https://regex101.com/r/gGrwuz/1)
[Teste den regulären Ausdruck](https://regex101.com/r/gGrwuz/1)

### 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
example, der reguläre Ausdruck `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.

<pre>
"c.+t" => The fat <a href="#learn-regex"><strong>cat sat on the mat</strong></a>.
</pre>

[Test the regular expression](https://regex101.com/r/Dzf9Aa/1)
[Teste den regulären Ausdruck](https://regex101.com/r/Dzf9Aa/1)

### 2.3.3 The Question Mark

In regular expression 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
For example, der reguläre Ausdruck `[T]?he` means: Optional the uppercase
letter `T`, followed by the lowercase character `h`, followed by the lowercase
character `e`.

<pre>
"[T]he" => <a href="#learn-regex"><strong>The</strong></a> car is parked in the garage.
</pre>

[Test the regular expression](https://regex101.com/r/cIg9zm/1)
[Teste den regulären Ausdruck](https://regex101.com/r/cIg9zm/1)

<pre>
"[T]?he" => <a href="#learn-regex"><strong>The</strong></a> car is parked in t<a href="#learn-regex"><strong>he</strong></a> garage.
</pre>

[Test the regular expression](https://regex101.com/r/kPpO2x/1)
[Teste den regulären Ausdruck](https://regex101.com/r/kPpO2x/1)

## 2.4 Braces

In regular expression braces that are 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
repeated. For example, der reguläre Ausdruck `[0-9]{2,3}` means: Match at least
2 digits but not more than 3 ( characters in the range of 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.
</pre>

[Test the regular expression](https://regex101.com/r/juM86s/1)
[Teste den regulären Ausdruck](https://regex101.com/r/juM86s/1)

We can leave out the second number. For example, the regular expression
We can leave out the second number. For example, der reguläre Ausdruck
`[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>
"[0-9]{2,}" => The number was 9.<a href="#learn-regex"><strong>9997</strong></a> but we rounded it off to <a href="#learn-regex"><strong>10</strong></a>.0.
</pre>

[Test the regular expression](https://regex101.com/r/Gdy4w5/1)
[Teste den regulären Ausdruck](https://regex101.com/r/Gdy4w5/1)

<pre>
"[0-9]{3}" => The number was 9.<a href="#learn-regex"><strong>999</strong></a>7 but we rounded it off to 10.0.
</pre>

[Test the regular expression](https://regex101.com/r/Sivu30/1)
[Teste den regulären Ausdruck](https://regex101.com/r/Sivu30/1)

## 2.5 Capturing Group

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
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
der reguläre Ausdruck `(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`,
For example, der reguläre Ausdruck `(c|g|p)ar` means: lowercase character `c`,
`g` or `p`, followed by character `a`, followed by character `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.
</pre>

[Test the regular expression](https://regex101.com/r/tUxrBG/1)
[Teste den regulären Ausdruck](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
Expand All @@ -278,14 +270,14 @@ language that implements regular expressions in a function definition.

A non-capturing group is a capturing group that only 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 parenthesis `(...)`. For example, der reguläre Ausdruck `(?: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>
"(?: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.
</pre>

[Test the regular expression](https://regex101.com/r/Rm7Me8/1)
[Teste den regulären Ausdruck](https://regex101.com/r/Rm7Me8/1)

Non-capturing groups can come in handy when used in find-and-replace functionality or
when mixed with capturing groups to keep the overview when producing any other kind of output.
Expand All @@ -308,7 +300,7 @@ in parentheses can be met and it will match.
"(T|t)he|car" => <a href="#learn-regex"><strong>The</strong></a> <a href="#learn-regex"><strong>car</strong></a> is parked in <a href="#learn-regex"><strong>the</strong></a> garage.
</pre>

[Test the regular expression](https://regex101.com/r/fBXyX0/1)
[Teste den regulären Ausdruck](https://regex101.com/r/fBXyX0/1)

## 2.7 Escaping special character

Expand All @@ -317,8 +309,8 @@ 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.

For example, the regular expression `.` is used to match any character except
newline. Now to match `.` in an input string the regular expression
For example, der reguläre Ausdruck `.` is used to match any character except
newline. Now to match `.` in an input string der reguläre Ausdruck
`(f|c|m)at\.?` means: lowercase letter `f`, `c` or `m`, followed by lowercase
character `a`, followed by lowercase letter `t`, followed by optional `.`
character.
Expand All @@ -327,7 +319,7 @@ character.
"(f|c|m)at\.?" => The <a href="#learn-regex"><strong>fat</strong></a> <a href="#learn-regex"><strong>cat</strong></a> sat on the <a href="#learn-regex"><strong>mat.</strong></a>
</pre>

[Test the regular expression](https://regex101.com/r/DOc5Nu/1)
[Teste den regulären Ausdruck](https://regex101.com/r/DOc5Nu/1)

## 2.8 Anchors

Expand All @@ -352,13 +344,13 @@ lowercase character `h`, followed by lowercase character `e`.
"(T|t)he" => <a href="#learn-regex"><strong>The</strong></a> car is parked in <a href="#learn-regex"><strong>the</strong></a> garage.
</pre>

[Test the regular expression](https://regex101.com/r/5ljjgB/1)
[Teste den regulären Ausdruck](https://regex101.com/r/5ljjgB/1)

<pre>
"^(T|t)he" => <a href="#learn-regex"><strong>The</strong></a> car is parked in the garage.
</pre>

[Test the regular expression](https://regex101.com/r/jXrKne/1)
[Teste den regulären Ausdruck](https://regex101.com/r/jXrKne/1)

### 2.8.2 Dollar

Expand All @@ -371,13 +363,13 @@ character and the matcher must be end of the string.
"(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>
</pre>

[Test the regular expression](https://regex101.com/r/y4Au4D/1)
[Teste den regulären Ausdruck](https://regex101.com/r/y4Au4D/1)

<pre>
"(at\.)$" => The fat cat. sat. on the m<a href="#learn-regex"><strong>at.</strong></a>
</pre>

[Test the regular expression](https://regex101.com/r/t0AkOd/1)
[Teste den regulären Ausdruck](https://regex101.com/r/t0AkOd/1)

## 3. Shorthand Character Sets

Expand Down Expand Up @@ -421,7 +413,7 @@ 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
the equal sign inside parentheses. For example, der reguläre Ausdruck
`(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`
Expand All @@ -431,7 +423,7 @@ or `the` which are followed by the word `fat`.
"(T|t)he(?=\sfat)" => <a href="#learn-regex"><strong>The</strong></a> fat cat sat on the mat.
</pre>

[Test the regular expression](https://regex101.com/r/IDDARt/1)
[Teste den regulären Ausdruck](https://regex101.com/r/IDDARt/1)

### 4.2 Negative Lookahead

Expand All @@ -447,7 +439,7 @@ character.
"(T|t)he(?!\sfat)" => The fat cat sat on <a href="#learn-regex"><strong>the</strong></a> mat.
</pre>

[Test the regular expression](https://regex101.com/r/V32Npg/1)
[Teste den regulären Ausdruck](https://regex101.com/r/V32Npg/1)

### 4.3 Positive Lookbehind

Expand All @@ -460,7 +452,7 @@ from input string that are after the word `The` or `the`.
"(?<=(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>.
</pre>

[Test the regular expression](https://regex101.com/r/avH165/1)
[Teste den regulären Ausdruck](https://regex101.com/r/avH165/1)

### 4.4 Negative Lookbehind

Expand All @@ -473,7 +465,7 @@ string that are not after the word `The` or `the`.
"(?&lt;!(T|t)he\s)(cat)" => The cat sat on <a href="#learn-regex"><strong>cat</strong></a>.
</pre>

[Test the regular expression](https://regex101.com/r/8Efx5G/1)
[Teste den regulären Ausdruck](https://regex101.com/r/8Efx5G/1)

## 5. Flags

Expand All @@ -492,48 +484,48 @@ integral part of the RegExp.
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
the `i` flag tells the regular expression engine to ignore the case. As you can
the `i` flag tells der reguläre Ausdruck engine to ignore the case. As you can
see we also provided `g` flag because we want to search for the pattern in the
whole input string.

<pre>
"The" => <a href="#learn-regex"><strong>The</strong></a> fat cat sat on the mat.
</pre>

[Test the regular expression](https://regex101.com/r/dpQyf9/1)
[Teste den regulären Ausdruck](https://regex101.com/r/dpQyf9/1)

<pre>
"/The/gi" => <a href="#learn-regex"><strong>The</strong></a> fat cat sat on <a href="#learn-regex"><strong>the</strong></a> mat.
</pre>

[Test the regular expression](https://regex101.com/r/ahfiuh/1)
[Teste den regulären Ausdruck](https://regex101.com/r/ahfiuh/1)

### 5.2 Global search

The `g` modifier is used to perform a global match (find all matches rather than
stopping after the first match). For example, the regular expression`/.(at)/g`
stopping after the first match). For example, der reguläre Ausdruck`/.(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).
der reguläre Ausdruck now it will 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.
</pre>

[Test the regular expression](https://regex101.com/r/jnk6gM/1)
[Teste den regulären Ausdruck](https://regex101.com/r/jnk6gM/1)

<pre>
"/.(at)/g" => The <a href="#learn-regex"><strong>fat</strong></a> <a href="#learn-regex"><strong>cat</strong></a> <a href="#learn-regex"><strong>sat</strong></a> on the <a href="#learn-regex"><strong>mat</strong></a>.
</pre>

[Test the regular expression](https://regex101.com/r/dO1nef/1)
[Teste den regulären Ausdruck](https://regex101.com/r/dO1nef/1)

### 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
`m` flag. For example, der reguläre Ausdruck `/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
at the end of each line in a string.
Expand All @@ -544,15 +536,15 @@ at the end of each line in a string.
on the <a href="#learn-regex"><strong>mat.</strong></a>
</pre>

[Test the regular expression](https://regex101.com/r/hoGMkP/1)
[Teste den regulären Ausdruck](https://regex101.com/r/hoGMkP/1)

<pre>
"/.at(.)?$/gm" => The <a href="#learn-regex"><strong>fat</strong></a>
cat <a href="#learn-regex"><strong>sat</strong></a>
on the <a href="#learn-regex"><strong>mat.</strong></a>
</pre>

[Test the regular expression](https://regex101.com/r/E88WE2/1)
[Teste den regulären Ausdruck](https://regex101.com/r/E88WE2/1)

## 6. Greedy vs lazy matching
By default regex will do greedy matching , means it will match as long as
Expand All @@ -562,13 +554,13 @@ possible. we can use `?` to match in lazy way means as short as possible
"/(.*at)/" => <a href="#learn-regex"><strong>The fat cat sat on the mat</strong></a>. </pre>


[Test the regular expression](https://regex101.com/r/AyAdgJ/1)
[Teste den regulären Ausdruck](https://regex101.com/r/AyAdgJ/1)

<pre>
"/(.*?at)/" => <a href="#learn-regex"><strong>The fat</strong></a> cat sat on the mat. </pre>


[Test the regular expression](https://regex101.com/r/AyAdgJ/2)
[Teste den regulären Ausdruck](https://regex101.com/r/AyAdgJ/2)


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