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Q&A

Vim: how to search for all instances of a string, except for those that are between two specific strings

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Using Vim, I am trying to search for all instances of a specific string, except for those that fall somewhere in between two other specific strings.

For example, I want to determine all instances of bird, except for those that fall somewhere between abc and xyz. So in the text below, a successful command would find only the 1st and 3rd instances of bird on line 1, and only the 1st instance of bird on line 2:

bird ant abc cow bird xyz cat bird
cat dog fish bird abc bird horse xyz

my best efforts:

This search seems to find all instances of bird that do not have xyz somewhere after them:

/bird\(.*xyz\)\@!

This search seems to find all instances of bird that do not have abc somewhere before them (a similar example is shown in :help \@<!)

/\(abc.*\)\@<!bird

But naively trying to combine these two patterns does not work:

/\(abc.*\)\@<!bird\(.*xyz\)\@!
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2 answers

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Alternating between the two patterns seems to work!

\(abc.*\)\@<!bird\|bird\(.*xyz\)\@!

As a bonus, you can enable the very magic mode with \v to avoid backslashes! The resulting expression is equivalent but easier to type.

\v(abc.*)@<!bird|bird(.*xyz)@!

For reference: :help /bar and :help \v.

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As @Quasímodo‭ has shown, the search pattern \(abc.*\)\@<!bird\|bird\(.*xyz\)\@! solves your problem. But, why does it work, and why does your original approach not work?

What you want to achieve is to find all occurrences of "bird" for which the following holds:

"bird" if not between "abc" and "xyz"

Which can be re-phrased as

"bird" if not ((preceded by "abc") and (followed by "xyz"))

Or, using De Morgan's law:

"bird" if ((not preceded by "abc") or (not followed by "xyz"))
<==> (bird if not preceded by "abc") or (bird if not followed by "xyz")

This is why @Quasímodo‭'s answer works.

Your search pattern /\(abc.*\)\@<!bird\(.*xyz\)\@!, however, has the following meaning:

bird, if ((not preceded by "abc") AND (not followed by "xyz"))

In other words, an occurrence of "bird" will be ignored if there is a preceding "abc" or a following "xyz". You will see this when trying your original expression on the following line:

foo bird bar

This occurrence of bird will be found.

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