<B style="color:black;background-color:#A0FFFF">Postscript</B> is a programming language (in reverse polish notation, see RPN in Tcl) that is used mostly for representing printable documents. More decent printers usually understand (interpret) <B style="color:black;background-color:#A0FFFF">Postscript</B> right away.
Popular tools to visualize <B style="color:black;background-color:#A0FFFF">Postscript </B><B style="color:black;background-color:#99ff99">files</B> are ghostscript/ghostview [L1 ].
The <B style="color:black;background-color:#A0FFFF">Postscript</B> Language Reference Manual and some related specifications can be found at [L2 ].
Syntax in brief: Words are separated by whitespace, but the ten special characters %/(){}[]<> also end the previous word (with some exceptions). % starts a comment, that continues to the end of the line. / before a word makes that word literal (prevents that it is executed). Parentheses delimit strings; \ is escape character in strings. Braces delimit procedures (executable arrays); they work sort of like in Tcl. Brackets construct normal arrays, which are similar to lists in Tcl, except that they have fixed length :-(. The PS code
a [b /c /d e] f
is sort of equivalent to Tcl
$a [list $b c d $e] $f
or (if f is more of a command than a variable)
f $a [list $b c d $e]
A typical <B style="color:black;background-color:#A0FFFF">Postscript</B> file starts with a %! comment, and it usually contains a couple of %% comments that contain markup for programs that manipulate <B style="color:black;background-color:#A0FFFF">Postscript </B><B style="color:black;background-color:#99ff99">files</B>.
%! %%Creator: Gif2PS /#copies 1 def
The last line is an assignment: "assign to the variable #copies the value 1", or set #copies 1 as we would say in Tcl.
See also Manipulating <B style="color:black;background-color:#A0FFFF">Postscript</B>