In Vim, how do you search for a word boundary character, like the \b in regexp?

/the\>

See :help /ordinary-atom

I assume "regexp" means PCRE. It is worth noting that Vim's regex syntax differs from (and apparently predates) PCRE.

See also:

• Why does VIM have its own regex syntax?
• What's the difference between vim regex and normal regex?
• Within vim's regex engine, why are some metacharacters escaped and some are not?
• Can I make vim accept \b rather than just \< and \>?

Use \< and \> for word start and word end, respectively.

E.g. In your specific case you would use:

/the\>/

If very magic is turned on, then you shouldn't escape the > character. See what's magic search. SO in your case you'd do:

/\v<the>

it would search for only the word 'the'.

if you are trying to search a word at your cursor. you can just hit *, or # for backward search.