The multiline mode is enabled by the flag m
.
It only affects the behavior of ^
and $
.
In the multiline mode they match not only at the beginning and the end of the string, but also at start/end of line.
Searching at line start ^
In the example below the text has multiple lines. The pattern /^\d/gm
takes a digit from the beginning of each line:
let str = `1st place: Winnie
2nd place: Piglet
3rd place: Eeyore`;
alert( str.match(/^\d/gm) ); // 1, 2, 3
Without the flag m
only the first digit is matched:
let str = `1st place: Winnie
2nd place: Piglet
3rd place: Eeyore`;
alert( str.match(/^\d/g) ); // 1
That???s because by default a caret ^
only matches at the beginning of the text, and in the multiline mode ??? at the start of any line.
???Start of a line??? formally means ???immediately after a line break???: the test ^
in multiline mode matches at all positions preceded by a newline character \n
.
And at the text start.
Searching at line end $
The dollar sign $
behaves similarly.
The regular expression \d$
finds the last digit in every line
let str = `Winnie: 1
Piglet: 2
Eeyore: 3`;
alert( str.match(/\d$/gm) ); // 1,2,3
Without the flag m
, the dollar $
would only match the end of the whole text, so only the very last digit would be found.
???End of a line??? formally means ???immediately before a line break???: the test $
in multiline mode matches at all positions succeeded by a newline character \n
.
And at the text end.
Searching for \n instead of ^ $
To find a newline, we can use not only anchors ^
and $
, but also the newline character \n
.
What???s the difference? Let???s see an example.
Here we search for \d\n
instead of \d$
:
let str = `Winnie: 1
Piglet: 2
Eeyore: 3`;
alert( str.match(/\d\n/gm) ); // 1\n,2\n
As we can see, there are 2 matches instead of 3.
That???s because there???s no newline after 3
(there???s text end though, so it matches $
).
Another difference: now every match includes a newline character \n
. Unlike the anchors ^
$
, that only test the condition (start/end of a line), \n
is a character, so it becomes a part of the result.
So, a \n
in the pattern is used when we need newline characters in the result, while anchors are used to find something at the beginning/end of a line.