Re: basename is not working as expected if invoked in `` inside a find subcommand

[Andreas R.]

Paul Jarc wrote:
>>> find dir1 -exec diff -q "{}" dir2/`basename {}` \;
>
> Here, the command substitution is expanded by the shell before find
> runs.  basename sees the literal argument {}, and so it outputs {},
> and find sees dir2/{}.
>
>>> find dir1 -exec sh -c "diff -q {} dir2/`basename {}`" \;
>
> Here, agin, the command substitution is expanded before find runs.
> Double quotes don't prevent an inner command substitution from being
> expanded.  Single quotes will, though.  This will do what you want:
>
> find dir1 -exec sh -c 'diff -q {} dir2/`basename {}`' \;
That works. Thanks a lot for the advice and explanation, Paul.

> But if the filename contains any whitespace or shell metacharacters,
> it'll cause trouble.  You can protect against that like this:
>
> find dir1 -exec sh -c 'diff -q "$0" dir2/"`basename "$0"`"' {} \;
Wow. Rewritten in the form
  find dir1 -type f -exec sh -c 'echo "{}" dir2/"`basename "{}"`"' \;
it works, but I still don't understand completely why it works.
The first part "{}" is clear (I think), but how do we get to "`basename "{}"`"
? What is the reason why "`basename {}`" doesn't work? And where do you learn
such tricks from? :)
Is there a book you would suggest (or was reading the man page enough)?

Regards,
Andreas