Postscript: concatenate two strings?

Question

How do I concatenate two strings in Postscript?

(foo) (bar) ??? -> (foobar)

Answer 1

PostScript doesn't have a built-in string concatenation operator. You need to write some code for that. For instance

 /concatstrings % (a) (b) -> (ab)  
   { exch dup length    
     2 index length add string    
     dup dup 4 2 roll copy length
     4 -1 roll putinterval
   } bind def  

(code from https://en.wikibooks.org/wiki/PostScript_FAQ/Programming_PostScript#How_to_concatenate_strings%3F.)

Answer 2

Same idea generalized to any number of strings. Earlier revisions use a helper function acat which takes an array of strings (for easy counting and iteration). This version uses fancier loops and stack manipulation to avoid allocating an array. This version would also concatenate arrays by changing the string operator to array.

% (s1) (s2) (s3) ... (sN) n  ncat  (s1s2s3...sN)
/ncat {        % s1 s2 s3 .. sN n                   % first sum the lengths
    dup 1 add  % s1 s2 s3 .. sN n n+1 
    copy       % s1 s2 s3 .. sN n  s1 s2 s3 .. sN n
    0 exch     % s1 s2 s3 .. sN n  s1 s2 s3 .. sN 0 n 
    {   
        exch length add 
    } repeat             % s1 s2 s3 .. sN  n   len  % then allocate string
    string exch          % s1 s2 s3 .. sN str   n   
    0 exch               % s1 s2 s3 .. sN str  off  n
    -1 1 {               % s1 s2 s3 .. sN str  off  n  % copy each string
        2 add -1 roll       % s2 s3 .. sN str  off s1  % bottom to top
        3 copy putinterval  % s2 s3 .. sN str' off s1
        length add          % s2 s3 .. sN str' off+len(s1)
                            % s2 s3 .. sN str' off'
    } for                               % str' off'
    pop  % str'
} def 

(abc) (def) (ghi) (jkl) 4 ncat == %(abcdefghijkl)

Answer 3

There are useful subroutines in

http://www.jdawiseman.com/papers/placemat/placemat.ps

including Concatenate (accepting two strings) and ConcatenateToMark (mark string0 string1 …).