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Add repetitions meta character

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Zeeshan Ahmed 2017-07-23 12:06:54 +01:00
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@ -54,18 +54,18 @@ The meta character are as follows:
|Meta character|Description| |Meta character|Description|
|:----:|----| |:----:|----|
|<b>.</b>|Period matches any single character except a line break.| |.|Period matches any single character except a line break.|
|<b>[ ]</b>|Character class. Matches any character contained between the square brackets.| |[ ]|Character class. Matches any character contained between the square brackets.|
|<b>[^ ]</b>|Negated character class. Matches any character that is not contained between the square brackets| |[^ ]|Negated character class. Matches any character that is not contained between the square brackets|
|<b>*</b>|Matches 0 or more repetitions of the preceding symbol.| |*|Matches 0 or more repetitions of the preceding symbol.|
|<b>+</b>|Matches 1 or more repetitions of the preceding symbol. |+|Matches 1 or more repetitions of the preceding symbol.
|<b>?</b>|Makes the preceding symbol optional.| |?|Makes the preceding symbol optional.|
|<b>{n}</b>|Braces. Matches “n” repetitions of the preceding symbol.| |{n}|Braces. Matches “n” repetitions of the preceding symbol.|
|<b>(xyz)</b>|Character group. Matches the characters xyz in that exact order.| |(xyz)|Character group. Matches the characters xyz in that exact order.|
|<b>&#124;</b>|Alternation. Matches either the characters before or the characters after the symbol.| |&#124;|Alternation. Matches either the characters before or the characters after the symbol.|
|<b>&#92;</b>|Escapes the next character. This allows you to match reserved characters <code>[ ] ( ) { } . * + ? ^ $ \ &#124;</code>| |&#92;|Escapes the next character. This allows you to match reserved characters <code>[ ] ( ) { } . * + ? ^ $ \ &#124;</code>|
|<b>^</b>|Matches the beginning of the input.| |^|Matches the beginning of the input.|
|<b>$</b>|Matches the end of the input.| |$|Matches the end of the input.|
## 2.1 Full stop ## 2.1 Full stop
@ -87,6 +87,12 @@ expression `[Tt]he` means: an uppercase `T` or lowercase `t`, followed by the le
"[Tt]he" => <strong><u>The</u></strong> car parked in <strong><u>the</u></strong> garage. "[Tt]he" => <strong><u>The</u></strong> car parked in <strong><u>the</u></strong> garage.
</pre> </pre>
Just like above example the regular expression `ar[.]` means: an lowercase character `a`, followed by letter `r`, followed by any character.
<pre>
"ar[.]" => The car p<strong><u>ark</u></strong>ed in the g<strong><u>ara</u></strong>ge.
</pre>
### 2.2.1 Negated character set ### 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 In general the caret symbol represents the start of the string, but when it is typed after the opening square bracket it negates the
@ -98,11 +104,49 @@ the letter `r`.
</pre> </pre>
### 2.2.2 Repeating character set ## 2.3 Repetitions
We can repeat a character class by using `+`, `*` or `?` operators. For example the regular expression `[a-z]+` means: any number of Following meta characters `+`, `*` or `?` are used to specify how many times a subpattern can occurs. These meta characters act
lowercase letters in a row. 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 character `a`. But if it apperas after a character set or class that 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.
<pre> <pre>
"[a-z]+" => <strong><u>The</u></strong> <strong><u>car</u></strong> <strong><u>parked</u></strong> <strong><u>in</u></strong> <strong><u>the</u></strong> <strong><u>garage</u></strong>. "[a-z]*" => <strong><u>The</u></strong> <strong><u>car</u></strong> <strong><u>parked</u></strong> <strong><u>in</u></strong> <strong><u>the</u></strong> <strong><u>garage</u></strong> #21.
</pre> </pre>
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`, followed by
zero or more spaces.
<pre>
"\s*cat\s*" => The fat<strong><u> cat </u></strong>sat on the <strong><u>cat</u></strong>.
</pre>
### 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 any number of character, followed by the lowercase character `t`.
<pre>
"c.+t" => The fat <strong><u>cat sat on the mat</u></strong>.
</pre>
### 2.3.3 The Question Mark
In regular expression the meta character `?` makes the preceding character optional. This symbol matches zero or more repetitions 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`.
<pre>
"[T]he" => <strong><u>The</u></strong> car is parked in the garage.
</pre>
<pre>
"[T]?he" => <strong><u>The</u></strong> car is parked in t<strong><u>he</u></strong> garage.
</pre>