casperscript - ghostscript/postscript made friendlier for Python and C programmers

The goal is to make casperscript an extension of ghostscript optimized for general-purpose programming. I don't envision it used for embedded devices, although I won't deliberately code the extensions so as to prohibit such.

One of the first steps was to define '#!' as a comment, obviating having to use binfmt_misc and a wrapper script for the interpreter (because to process args, gs must be run as gs -- myfile.ps arg1 arg2).

This also required splitting the args, since linux returns multiple shebang-line args as a single string.

A change that turned out to be far simpler than expected got rid of the /undefined error, enabling easy top-down design: a placeholder is shown for any undefined words at time of command execution.

Now the primary goal is to give it the "batteries included" features from Python, so budding programmers don't have to "reinvent the wheel" just to perform simple tasks.

I was hoping to be able to hijack the entire parser so that '/' could be used for division and '#' for comments, on a per-file basis (so real postscript code can still be run), but that's going to take a back seat. Too complicated.

PLEASE NOTE that casperscript is optimized for utility, not safety; it uses the -dNOSAFER option to ghostscript, thus it is not suitable for server-side applications. See https://blog.redteam-pentesting.de/2023/ghostscript-overview/ for some of the reasons why.

ALSO PLEASE NOTE that casperscript is sometimes under active development, and changes to Resource/Init/casperscript.ps can break your programs. To avoid this, make sure to use versioned names in your shebang line, e.g. #!/usr/local/casperscript/bin/ccs-0cf34d05c rather than the unversioned names like cs, ccs, and bccs. The hex digits following the dash are the git commit, so you can always recreate the correct executable if needed.

John Comeau jc@unternet.net 2023-03-21

quickstart

Go to digitalocean.com, set up an account if you don't have one already, and spin up a $6/month Debian 11 droplet, the most basic configuration. It's less than a penny an hour, and you only pay for the time you use.

ssh root@droplet, where droplet is the IP number assigned to your Debian instance by digitalocean.

apt update
apt install git make autoconf gcc libreadline-dev libx11-dev x11-apps xauth libxext-dev libxt-dev
echo 'export PATH=$HOME/bin:$PATH' >> ~/.bashrc
^D  # logout, we'll log right back in with an X windows connection
ssh -Y root@droplet
cd /usr/src
git clone https://github.com/jcomeauictx/casperscript
cd casperscript
make
make install
csbin/echo just a test  # should echo 'just a test' on the following line
ccs  # should give you a `ccs>` prompt
ccs> (hello world!) =
hello world!
^D  # log out of ccs
xeyes  # make sure you have a working X connection, ^C out of it
cs examples/tiger.eps  # should show a beautiful color cartoon tiger

Don't forget to go back to digitalocean.com and delete (Destroy) your droplet!

developer info

Information for Ghostscript developers
error printing macros in base/std.h
if you, as I do, use vim as editor and name your casperscript files with a .cs extension, putting syntax=postscr in your modeline will fix the syntax highlighting, e.g.: % vim: tabstop=8 shiftwidth=2 expandtab softtabstop=2 syntax=postscr
use ##stack liberally while coding, to show the stack as an array during coding, even while coding the .ps files for casperscript itself.
when coding casperscript.cs itself, use the caspertest recipe in GNUmakefile to make sure it's compatible with vanilla gs, e.g.: make TESTCASPER='(this is) string.split' caspertest