Regex – match start and end of line
In this article, we will take a look at matching start and end of line and word with regular expressions.
In regex, we have following two characters for this
^ To match the start of a line, and
$ To match the end of line
These are called anchors, which do not have any length. Rather, they match a position: start or end.
Regex start of line
To check if a word or line starts with some character or pattern, ^(carat) is used.
This means that the test string should start with a character, regex should start with ^ and the character to test followed by other characters to test. Example,
^s[a-z] will match only those two characters in a word that start with s.
First character of match will be s and the character after s.
Note that if you want to check if a line or word starts with some character, then ^ should be the first character of regex.
It will not work, if placed between the regular expression. Examples are
| Expression | Examples | Description |
|---|---|---|
| ^s | Matches first character of soil, sand, shell | It will match first character of a line if it starts with ‘s’. |
| ^she | Matches 3 characters of she, shell, sheep | Will match 3 characters of a line or word that begins with ‘s’ followed by has ‘h’ and ‘e’. |
| ^s[a-z]* | Matches complete words soil, sand, shell etc. | Will match words that start with ‘s’ followed by all alphabets. For a multi word line, this will match the first word if the line starts with ‘s’. |
| ^s[a-z ]* | Matches words soil, soil is fertile etc. | Will match lines that start with ‘s’. |
| ^\d[a-z]* | Matches complete words 6balls, 2boys, 3girls etc. | Will match words that start with a number followed by all alphabets. For a multi word line, this will match the first word if the line starts with a number. |
| ^\d[a-z ]* | Matches words 6, 6 balls is one over etc. | Will match lines that start with a number. |
| ^[bc][a-z]* | Matches ball and call. | Will match |
Java – Regex start of line
If you are working in java and want to match a string that starts with some pattern programatically using regex, then you can use compile() and match() methods of Pattern class as shown below
// regex to match start of word with number
Pattern pattern = Pattern.compile("^\\d[a-z]*");
Matcher matcher = pattern.matcher("1over");
boolean matches = matcher.matches(); //true
To test if a word or line ends with a character or pattern,
$(dollar) anchor is used in regex.$ is applied at the end of regex and it will match those words or lines that end with the pattern just before $ symbol. Example,[a-z]1$ will match the last two characters of a word that ends with 1.
$ will not work, if placed between the regular expression. Examples are
| Expression | Examples | Description |
|---|---|---|
| $1 | Matches last character of ball1, sand23, shell12 | It will match last character of a word if it ends with 1. |
| tc[h$] | Matches the last 3 characters of match, catch, batch | Will match last 3 characters of a line or word that ends with ‘tch’. |
| [a-z]*w$ | Matches complete words how, cow, eyebrow etc. | Will match words that end with ‘w’. For a multi word line, this will match the last word if the line ends with ‘w’. |
| [a-z]*\d$ | Matches complete words run12, boys3, girls4 etc. | Will match words that end with a number. For a multi word line, this will match the last word if the line ends with a number. |
| [a-z ]*\d$ | Matches words 6, balls is one over are 6 etc. | Will match lines that end with a number. |
Java – Regex end of line
With java, you can use compile() and match() methods of Pattern class to match end of line with $ as shown below
// regex to match end of word with number
Pattern pattern = Pattern.compile("[a-z]*\\d$");
Matcher matcher = pattern.matcher("over6");
boolean matches = matcher.matches(); //true
Hope you understood how to match start and end of line with regex anchors.
Play around with different combinations to clarify further.