[MacPerl] Current Working directory (vs. directory where the script isrunning)

[Vicki Brown <vlb@cfcl.com>]

At 23:17 -0400 5/20/99, Ronald J Kimball wrote:
> If the current working directory is not the directory where the script is
> running, then what is it exactly?  I don't think we are using these terms
> in the same way.

this reminds me of "The Princess Bride" :-)
      "You keep using that word. I do not think it means what
       you think it means"

:-)
>   I don't think we are using these terms in the same way.

Probably not. However, since the term "current working directory" is
effectively meaningless under the Finder (and was invented long before the
Macintosh :), I think I'm justified in using the term the way Unix, MPW,
and other shell-oriented systems use it.

I had begun thinking that this discussion belonged more on macperl-anyperl
because I was specifically addressing the question of _portable code_ ...
but then I remembered MPW :-)  So this really _is_ a MacPerl discussion,
because Chris' statement:

  At 20:29 -0400 5/18/99, Chris Nandor wrote:
  > Current directory is where the script is.  It defaults to MacPerl's
  > location if the script is not saved to a file.

applies to the standalone MacPerl _app_. The MPW Perl tool, however, works
more like Unix, i.e. the current directory is where the USER is. Where the
SCRIPT is, may be totally different.

Under MPW (or Unix :), the "current directory" is where you are. The MacOS
Finder analog (a pretty poor analog) would be the current window.  But of
course, you move the mouse to launch a command, so the window moves. The
MacPerl app emulates the "current directory" in a world that really doesn't
possess the concept of "current directory".

In Unix, or MPW, or any command line / shell environment, you (the user)
stay in a particular directory and run commands by typing their names. The
shell finds the command on the command path and launches it.  Even if the
command is in a different directory (folder) than where you "are".

So for example with MPW, I can sit in the shell window and ask "where am I
now"

  dir
  mouse3*:Protected:Projex:MPW:MPW:vlb:

I can look at the files and directories there

  files
  :seq2bio:
  shell_relnote.pdf
  Worksheet.vlb

Note, no Perl scripts, no perl command here.
The MPW perl command lives elsewhere:

  which perl
  mouse3*:Protected:Projex:MPW:MPW:Tools:perl

even so, I can run it from "here" (my current working directory) and I
don't have to "go" anywhere because the shell finds the program and
launches it for me. It's one of the differences between a command interface
and a click interface.

  perl -e 'print `pwd`;'
  mouse3*:Protected:Projex:MPW:MPW:vlb

yep; that's where I am. Now suppose I have a Perl script that lives
elsewhere

  which foo.plx
  mouse3*:Protected:Projex:MPW:MPW:Tools:foo.plx

Here's the script:
  Perl -Sx "{0}" {"Parameters"}; Exit
  #!perl
  print "working directory is ", `pwd`, "\n";  # working directory
  print "script is in $0\n";                   # path to script

The first line tells MPW perl to execute the script with Perl.  OK, the
script is in the Tools folder (directory). I am in the vlb folder
(directory).  Let's run the script:

  foo.plx
  working directory is mouse3*:Protected:Projex:MPW:MPW:vlb

  script is in mouse3*:Protected:Projex:MPW:MPW:Tools:foo.plx

So you can see that the "current directory" and the "place where the script
resides" are NOT the same under MPW. They would be the same if I switched
my current working directory to the Tools directory:

  dir
  mouse3*:Protected:Projex:MPW:MPW:Tools:

  foo.plx
  working directory is mouse3*:Protected:Projex:MPW:MPW:Tools

  script is in :foo.plx

Hmmm... $0 is not the full path to the script anymore. If I want to
determine the full path to the script, I need to combine my knowledge of
the current directory with $0... simply using $0 does not give me the full
path. Using the current directory does not guarantee the location of the
script.

As long as you stick to the standalone Perl app, current directory will be
the same as where the script is running (bacause that was how Matthias
implemented current directory). But to be portable (to Unix, say, or to MPW
MacPerl), then it is NOT always the case that current directory is where
the script is. It's possible. It's not assured.

- Vicki






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