Extending the -x syntax

[pbsds]

I love fd, and use it almost daily. Especially do i love the easy-to-use -x syntax.
But i do often find myself doing tricks like fd ... -x sh -c 'foobar "$(basename "{//}")"' to get the basename of the parent directory.

I decided to have a look at the -x syntax, and I propose this extension:

The following placeholders are substituted before the command is executed:

     {}     path (of the current search result)

     {/}    basename (deprecated)

     {-}    basename

     {//}   parent directory

     {///}  parent parent directory (repeatable)

     {//-}  parent directory basename

     {.}    path without outermost file extension

     {..}   path without the two outermost file extensions (repeatable)

     {/.}   basename without file extension (deprecated)

     {-.}   basename without file extension

The changes are:

• Change basename from / to -, as it conflicts with parent name, deprecating the old syntax
• Enable repeated applications of / and . (related: -x option with basename format doesn't seem to work with extensions with two . in them #911)

This will change the general find-replace regex match from \{/*\.*\} to \{/*-?.*\}.

I kept two deprecations for backward-compatibility, as people most likely use fd in in scripts. After a while, the documentation of the deprecated syntax could be removed, but we could keep their implementation and yield a warning.

Also something we could discuss: Should it be possible to escape the syntax? Something like
fd . -x echo "{}\{}" could print myfile.txt{}

[sharkdp]

Thank you for writing this up. Our syntax is based on that of GNU parallel (https://www.gnu.org/software/parallel/), so I'd rather not introduce any breaking changes, because that would also mean we're not compatible with parallel anymore.

But maybe we can study their documentation/issue tracker to see if there are extensions to the syntax we have in fd?