Idea: magic quoting

[Ole Tange]

Quoting is a bitch. There is simply no correct way to Do What I Mean(tm).

Currently these do the same:

  parallel echo {} \> {} ::: 1
  parallel "echo {} > {}" ::: 1

And I think it makes good sense that you can choose to quote parts of
the expression if you want to. In the above case you want a space to
be given to the shell to evaluate.

But here:

  parallel perl -e 'print "$$/{}\n"' ::: 1 # This does not work

you clearly intended it to be interpreted as:

  parallel perl -e 'print\ \"\$\$/{}\\\n\"' ::: 1

I.e. the special chars in the 3rd argument should be quoted. -q will do that:

  parallel -q perl -e 'print "$$/{}\n"' ::: 1 # This works

Much worse is:

  parallel perl -e 'print "$$/{}\n"' \> {} ::: 1 # This does not work

Here you wanted some of the characters to be quoted and other not.

I am now thinking: Can we come up with a good heuristic for what
blocks the user wants quoted and what not? So:

  parallel --magic-quote perl -e 'print "$$/{}\n"' \> {} ::: 1 # This
does not work

would do:

  parallel perl -e 'print\ \"\$\$/{}\\\n\"' \> {} ::: 1

My initial idea was to find all blocks that have a space in them and
then quote those blocks unless there was only a single argument in
total (e.g. parallel "echo {} > {}" ::: 1)

Then I thought if we can do better by including all special shell
characters if they were not alone, so this would also work:

  parallel --magic-quote perl -e 'print"$$/{}\n"' \> {} ::: 1 # Note
the missing space after print

But how would we then deal with: >{} or >>{}

It is not clear to me if it is possible to make a better guess than
now, but maybe you have a good idea for a heuristic.


/Ole