Re: difference between ~ & ^ negation

[Bart Schaefer <schaefer@brasslantern.com>]

On Jan 1,  3:28pm, zzapper wrote:
>
> What are the advantages/differences between the two types of "ignore" ^ ~

The ^ operator is similar to *~ except that it has high precedence, so
the pattern following ^ (up to a slash) is excluded from the set of all
files in the same level of directory hierarchy; e.g. foo/^bar/baz looks
for baz in any subdirectory of foo except the subdirectory named bar.
Therefore the pattern may not contain a slash.

The ~ operator is very low precedence, so the entire directory search
(including descent into subdirectories) to the left of the tilde is
performed, and the pattern to the right of the tilde is tested against
each file or directory to exclude it from the final result.  This means
that the pattern to the right of the tilde is not actually a glob; a
wildcard in that pattern can match a slash in the tested name, and the
pattern may contain slashes.

Thus X~Z is nearly equivalent to X(e:'[[ $REPLY == Z ]] && reply=():').

To see advantages and disadvantages, consider two of your examples:

> ls -lt **/*~*vssver.scc(.om[1,20])  # excluding vssver.scc 
> ls -lt **/^vssver.scc(.om[1,20])    #  excluding vssver.scc (simpler) 

As you pointed out, the second case is simpler.  However, these are not
quite equivalent; the first one should be:

    ls -lt **/*~*/vssver.scc(.om[1,20])

Otherwise you also ignore "OLDvssver.scc" (for example), so the second
case is also easier to use correctly.  I find the most difficult thing
to remember about ~ is that actual globbing happens only on the left,
so the right side has to match the path names as simple strings.

On the other hand, suppose you want to ignore vssver.scc only in the
myproject subdirectory, but include it everywhere else:

    ls -lt **/*~*/myproject/vssver.scc

There's no way to express this with the ^ operator except by using two
globs and a qualifier:

    ls -lt **/^vssver.scc **/^myproject/vssver.scc(N)

(The qualifier avoids a "no match" error if there is no vssver.scc file
anywhere outside of myproject.)

Now suppose you want everything that's neither in myproject nor named
vssver.scc; these should all be equivalent:

    ls -lt **/^myproject/^vssver.scc
    ls -lt **/*~*/(myproject/*|vssver.scc)
    ls -lt **/^vssver.scc~*/myproject/*

But these next two are not, do you see why?

    ls -lt **/^myproject~*/vssver.scc
    ls -lt **/^myproject/*~*/vssver.scc

Important note: ^ is special only in cases where / is special (globs).