Re: Sesquicolon -- Note: Not a Bug

[Marius Vollmer <mvo@zagadka.ping.de>]

Miles Bader <miles@gnu.org> writes:

> On Sat, Aug 24, 2002 at 11:26:03PM -0600, Richard Stallman wrote:
> > I wonder if there is a way we could change Emacs so that it could run
> > properly with #!.  Here's an idea that might work: suppose that when
> > Emacs's stdin is a file, but there is no -batch option, it
> > automatically starts in batch mode and loads $0.  WIth that change,
> > maybe #!/usr/bin/emacs could work.
> 
> What's wrong with just adding a single option that has the necessary
> semantics?

Guile uses "\" as a 'meta-switch'.  It causes Guile to interpret the
second line of the script as options.  (The meta-switch originally
came from Scsh, I think.)  From the Guile manual:

   Thus, consider a script named `/u/jimb/ekko' which starts like this:
     #!/usr/local/bin/guile \
     -e main -s
     !#
     (define (main args)
             (map (lambda (arg) (display arg) (display " "))
                  (cdr args))
             (newline))

   Suppose a user invokes this script as follows:
     $ /u/jimb/ekko a b c

   Here's what happens:
   * the operating system recognizes the `#!' token at the top of the
     file, and rewrites the command line to:
          /usr/local/bin/guile \ /u/jimb/ekko a b c
     This is the usual behavior, prescribed by POSIX.

   * When Guile sees the first two arguments, `\ /u/jimb/ekko', it opens
     `/u/jimb/ekko', parses the three arguments `-e', `main', and `-s'
     from it, and substitutes them for the `\' switch.  Thus, Guile's
     command line now reads:
          /usr/local/bin/guile -e main -s /u/jimb/ekko a b c

   * Guile then processes these switches: it loads `/u/jimb/ekko' as a
     file of Scheme code (treating the first three lines as a comment),
     and then performs the application `(main "/u/jimb/ekko" "a" "b"
     "c")'.


   When Guile sees the meta switch `\', it parses command-line argument
from the script file according to the following rules:
   * Each space character terminates an argument.  This means that two
     spaces in a row introduce an argument `""'.

   * The tab character is not permitted (unless you quote it with the
     backslash character, as described below), to avoid confusion.

   * The newline character terminates the sequence of arguments, and
     will also terminate a final non-empty argument.  (However, a
     newline following a space will not introduce a final empty-string
     argument; it only terminates the argument list.)

   * The backslash character is the escape character.  It escapes
     backslash, space, tab, and newline.  The ANSI C escape sequences
     like `\n' and `\t' are also supported.  These produce argument
     constituents; the two-character combination `\n' doesn't act like
     a terminating newline.  The escape sequence `\NNN' for exactly
     three octal digits reads as the character whose ASCII code is NNN.
     As above, characters produced this way are argument constituents.
     Backslash followed by other characters is not allowed.


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