如何在Emacs中正则表达式搜索=，而不是> =，==，<=，！=，〜=等？

Question

I would like to do regexp search for the = character, which may or may not have spaces on either sides, and may be at the beginning or end of a line. I've tried a couple:

• = doesn't work because it matches == , >= , etc.
• [^<>=]=[^<>=] doesn't work because it captures the two characters immediately before and after the = character, which is undesirable
• I thought \\_< and \\_> might be useful but I cannot figure out what these are for

In Vim, there are \\zs and \\ze which denote the start and end of a match so that I can match against the surrounding characters only for context. But Emacs doesn't have these.

Is this possible with Emacs?

Answer 1

Your question is underspecified. What characters do you disallow just before and after = ? You allow space chars (what about other whitespace?). But do you allow only space chars (or whitespace)?

Eg, do you allow a=b to match? If so, then perhaps letters are not disallowed?

Once you specify clearly what chars you allow and disallow immediately before and after = , you can write the regexp. But since you want to "capture" only the = in the matching contexts you will need to use a regexp group for the = and retrieve only what it matches, after matching everything.

For example, [ ]*=[ ]* matches = possibly surrounded by space chars. But if you want to capture only the = in that context then you need to use [ ]*\\\\(=\\\\)[ ]* and then use (match-string 1) to get the = .

You also don't say whether you are matching text in a buffer or in a string.

And you don't say whether you want to do this interactively or from a Lisp program.

The exact code you need depends on these things. If interactively, eg, for search, you don't need to double backslashes. If a string instead of a buffer then you need to pass the string as a second argument to match-string .

In general, your question is underspecified, and the answer involves specifying these things - in particular, just what contexts you want to match (what chars are allowed before and after = ) and what part(s) of the matching contexts you want to retrieve (just the = or the = plus some of the chars before and after it).