Vim regexes are awesome

cobrawgl

Two years ago I wrote about how
Vim's regexes were no fun
compared to :perldo and :rubydo. Turns out I was wrong, it was just a matter of
not being used to them
.
Vim's regexes are very good. They have all of the good features of Perl/Ruby regexes, plus some extra features that don't make sense outside of a text editor, but are nonetheless very helpful in Vim.
Here are a few of the neat things you can do.
Very magic
Vim regexes are inconsistent when it comes to what needs to be backslash-escaped and what doesn't, which is the one bad thing. But Vim lets you put \v to make everything suddenly consistent: everything except letters, numbers and underscores becomes "special" unless backslash-escaped.
Without \v:
:%s/^\%(foo\)\{1,3}\(.\+\)bar$/\1/
With \v:
:%s/\v^%(foo){1,3}(.+)bar$/\1/
Far easier to read. Along with \c to turn on and off case sensitivity, these are good options to make a habit of prepending to regexes when needed. It eventually becomes second-nature. See also :h /\v
Spanning newlines
One thing that :perldo and :rubydo can't do is span newlines; you can't combine two lines and you can't break one line into two.
But Vim's regexes can span newlines if you use \_. instead of .. I find this to be a lot more aesthetically pleasing than Perl's horrible s and m modifiers tacked onto the end of a regex. e.g. this strips  tags from a text document.
:%s@\v(\_.+)\V@\1@
(Note: in real life, never use a regex to parse HTML or XML. Down that path lies madness. The above is OK because I'd expect only one  tag to appear in any document.)
(Note^2: being able to turn on and off magic in the middle of a regex is awfully helpful.)
(Note^4: You can use arbitrary delimiters like @ for the regex, which is useful if your pattern includes literal /'s.)
See also :h \_.
\zs
Vim lets you demand that some text match, but ignore that text when it comes to the substitution part. This is handy for certain specific kinds of regexes. Normally if you want to match some text and then leave it alone in the substitution, you have to capture it and then put it back manually; \zs lets you avoid this.
Say you want to chop some text off the end of a line, but leave the rest of the line alone. Normally you'd have to do this:
:%s/\v^(foobar)(baz)/\1/
to put the foobar back. Of course you can also use a zero-width lookbehind assertion:
:%s/\v(^foobar)@
But that's even more line-noise. This is the easiest way:
:%s/^foobar\zsbaz//
See :h /\zs. (And :h /\@ if you're so inclined.)
Expressions
Using \=, you can put arbitrary expressions on the right side of a regex substitution. For example say you have this text:
~/foo ~/bar
If you do this:
:%s/\v(\S+)/\=expand(submatch(1))/g
You end up with:
/home/user/foo /home/user/bar
Because you can also call your own user-defined functions in the expression part, this can end up being pretty powerful. For example it can be used to
insert incrementing numbers
into arbitrary places in your text. See :h sub-replace-\=.
And so on
Read :h regexp if you haven't already. Tons of other features in there that can make your life easy if you manage to internalize them. It is difficult to get used to Vim's funky syntax if you're very familiar with Perl/Ruby-style regexes, but I think it's worth it. Only took me two years! (OK, more like a couple days of concerted effort after a year-and-a-half delay.)


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