两个正则表达式字符\\ b和\\有什么区别

Question

In the script I'm reading about regular expressions it says:

• '\\b' hits the front border of the word
• '\\<' hits the start of the word

So what's the difference in using the following

• \\b over \\<
• \\b over \\>

Answer 1

My man grep tells me about \\b :

The symbols \\< and \\> respectively match the empty string at the beginning and end of a word. The symbol \\b matches the empty string at the edge of a word, [...]

So \\bfoo\\b would match wherever \\<foo\\> would match.

On the other hand: There are so many regexp variants, that it is hard to tell what yours is doing with \\b .

Answer 2

\\b is like \\< and \\> combined:

• \\< match at beginning of word,
• \\> match at end of word,
• \\b match at the begining OR end of word,
• \\B matches except at the beginning or end of a word.

Answer 3

Your source appears to be wrong, or at least incomplete. \\b matches any border, not just the front one. Quote man grep :

The symbols \\< and \\> respectively match the empty string at the beginning and end of a word. The symbol \\b matches the empty string at the edge of a word

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• grep 's \\b is equivalent to grep 's \\(\\<\\|\\>\\)

In case you are familiar with Perl regular expressions,

• grep 's \\< is equivalent to Perl's (?<!\\w)(?=\\w)
• grep 's \\> is equivalent to Perl's (?<=\\w)(?!\\w)
• grep 's \\b is equivalent to Perl's \\b
• grep 's \\b is equivalent to Perl's (?:(?<!\\w)(?=\\w)|(?<=\\w)(?!\\w))