/ it /和/ \ Ait \ Z /有什么区别

Question

In Ruby both expressions seem to do similar things:

'it' =~ /^it$/   # 0
'it' =~ /\Ait\Z/ # 0
# but
/^it$/ == /\Ait\Z/ # false

So I an wondering what is the difference between ^ - \\A and $ - \\Z and how to choose which one to use?

Answer 1

The difference is only important when the string you are matching against can contain new lines. \\A matches the start of a string. ^ matches either the start of a string or immediately after a new line. Similarly \\Z only matches the end of the string, but $ matches the end of the string or the end of a line.

For example, the regular expression /^world$/ matches the second line of "hello\\nworld" but the expression /\\Aworld\\Z/ fails to match.

Answer 2

In regex engines that support multi-line regular expressions, ^ and $ are usually used for start and end of line markers.

\\A and \\Z are for start and end of string markers.

For example, the string:

Hello, my names
are Bob and James

would match ames$ twice (for names and James) but ames\\Z only once (for James).

Answer 3

^ - start of line
\\A - start of string

$ - end of line
\\Z - end of string