Curlfish - The CRLF shell

    This  is  curlfish,  a program just about as simple as they
    come.  The name comes from  an expansion of an abbreviation 
    of "CR/LF shell"

    What  is  a "CR/LF shell"? And why did I bother doing this?
    Well, years ago as a sysadmin, a user came  to  me  with  a
    puzzling  error:   his  shell  script was doing nothing but
    printing ": File not found /bin/ksh"

    This was really  strange,  because  /bin/ksh  certainly did
    exist!  After  a little investigation, I discovered that he
    had transferred the file up to the unix server (running HP-
    UX  10.20,  IIRC)  via FTP from his windows desktop PC, and
    had done so in binary mode.   Consequently,his  script  was
    full  of  CR/LF  line  endings,  and when it ran, the shell
    found the shebang line "#!/bin/ksh^M".  Naturally, when the
    shell  could find no file of that name, it ceased executing
    the script, and printed this 4-part error message:

    ksh: ./myscript: /bin/ksh^M: File not found
     ^        ^          ^             ^
     1        2          3             4

    Needless to say, the ^M was interpreted by the terminal  as
    a  carriage return, and the error message began overwriting
    itself from the start of the line.  By  a  weird  quirk  of
    coincidence,  part  4  of  the  error message was just long
    enough to completely overwrite parts 1 and 2 while  leaving
    part  3  pretty  much  intact,  resulting  in  the slightly
    cryptic message shown earlier.

    So I hit upon the idea of installing a program called ksh^M
    that  merely  printed  an  error message explaining exactly
    what must have happened and then exited. curlfish  is  just
    such a program.

    In fact, curlfish is no more than "Hello World!".  The real
    hack  is  in  filenames  (filenames  of   symbolic   links,
    actually).   The  actual  binary  is installed wherever you
    like and you make multiple symlinks to  it,  named  exactly
    the  same as real script interpreters, except followed by a
    carriage return character.  Thus, when a  file  is  created
    under  DOS  or Windows, and has CRLF line terminations, the
    script has a valid interpreter to call via its #! line.

    For example:
    /bin/ksh^M -> /usr/local/bin/curlfish
    /bin/csh^M -> /usr/local/bin/curlfish
    /usr/bin/perl^M -> /usr/local/bin/curlfish
    /usr/local/bin/ruby^M -> /usr/local/bin/curlfish

    (etc.)

    Actually creating filenames with those characters  is  left
    as  an  exercise for the reader.  There are several ways of
    doing so.

    I have also added a fairly distinctive return code (29), so
    that  if  scripts  that call curlfish are called by methods
    other than a direct shell  invocation,  that  fact  can  be
    tested  for  and the error handled gracefully.  This might,
    perhaps, be useful in build systems.

    So there it is at last - a somewhat  practical  use  for  a
    "Hello World!" program!


    --

    blubrick, 15/05/16