- Specify a starting or ending point that needs to be considered when searching for a pattern.
^
$
\A
- Start of a string, never the end of a line.
\Z End of a string, never the end of a line.
- The
^ character also indicates a negative character set.
- Start and End Anchors.
- Reference a position, not an actual character.
- They are known as
Zero-width
- Just telling you the pattern, the string and its position.
- An example is
/^apple/ or /\Aapple/
- To enture it is the first word in the string, we can add the caret
^ at the beginning, to ensure it is at the front of the string.
- If the word is somewhere else in the string, it will not match.
- The same is true for the
\A
- Another example is
/apple$/ or /apple\Z/
- Use the
$ sign to incicate it should be at the end of a string.
- Only finds a match, if it is the last 5 characters of that string.
\Z works in the same way.
- A third example is
/^apple$/ or /\Aapple\Z/
- The regular expression should completely define the string we’re looking at.
- From the beginning to the end.
^ and $ are support in all regex engines. \A and \Z are newer however.
- The exception to the above is JavaScript.
- PCRE –> Perl Compatible Regular Expression.
- Many programming languages use this.
- This supports all 4 types of regex listed above.
/^def/ only matches “def” out of “defabcdef”, it will not match the second “def” in the string./def$/ will only match the end of string such as “defadefdef” and ignore the first “def”.- For example with
/apples\Z/ this will match the last “apples” in “apples to apples to apples”
- Javascript will not recognise this.
- Can also define the entire string with
/\Aapples\Z/ which only matches “apples” because the entire string has been defined.
- Literally defines it from A-Z
- The next example is
/\w+@\w+\.[a-z]{3} which matches “someone@nowhere.com”.