scheme system stdout and markup predicates

[Jan-Peter Voigt]

Hello List,

I am using the scheme system command (on linux) to generate barcodes to 
include in the PDF:
--snip--
\version "2.14.2"

% use barcode command to produce temporary eps and include it
#(define-markup-command (barcode layout props type str size 
nums)(string-or-symbol? string? number-pair? boolean?)
  (let ((width (car size))
        (height (cdr size)))
       ; create temporary file name and empty stencil
       (let ((tmp (format "~A-~2A.eps" (strftime "%Y%m%d%H%M%S" 
(localtime (current-time))) (random 100)))
             (barcode-stencil (interpret-markup layout props (markup 
#:with-color red #:filled-box (cons 0 width) (cons 0 height) 0.7))))
            ; if str is a symbol like 'header:ismn get the property
            (if (symbol? str)(let ((tmp (chain-assoc-get str props #f)))
                     (if tmp (set! str tmp))))
            ; execute command
            (system (format "barcode ~A -e \"~A\" -g ~Ax~A+0+0 -o 
\"~A\" -E -b \"~A\"" (if nums "" "-n") type (* 100 width) (* 100 height) 
tmp str))
            ; create EPS stencil
            (set! barcode-stencil (eps-file->stencil X (car size) tmp))
            ; remove temporary file
            (system (format "rm -v \"~A\"" tmp))
            barcode-stencil
)))

% define stencil cache, to produce it only once, when used several times 
e.g. in footer markup
#(define-public (get-stencil symbol) #f)
#(define-public (put-stencil symbol stencil) #f)
#(define-public (rem-stencil symbol) #f)
#(let ((cache (list)))
     (set! put-stencil (lambda (symbol stencil)
               (set! cache (assoc-set! cache symbol stencil))
               stencil))
     (set! get-stencil (lambda (symbol)
               (assoc-get symbol cache)))
     (set! rem-stencil (lambda (symbol)
               (set! cache (assoc-set! cache symbol #f))
               empty-stencil))
)
#(define-markup-command (cache layout props sym text)(symbol? markup?)
  (let ((stencil (get-stencil sym)))
       (if (not stencil)
           (set! stencil (interpret-markup layout props text)))
       (put-stencil sym stencil)
       stencil)
)
#(define-markup-command (cache-clear layout props sym)(symbol?)
  (rem-stencil sym)
)

% include ISMN barcode
\markup \column {
  \cache #'ismn \barcode #"EAN" #"979000000121" #'(30 . 8) ##t
  \cache #'ismn \barcode #"EAN" #"979000000122" #'(35 . 8) ##t
  \cache-clear #'ismn
  \cache #'ismn \barcode #"EAN" #"979000000123" #'(40 . 8) ##t
}
--snip--

I have two questions:
To (system "...")
1: There are several commands, wich can write the generated EPS to 
stdout. Is there a possibility to catch that and integrate it without 
creating a temporary file?
2: Is there a way to get the result code and see if the command succeded?

Now have fun, playing around with (system "echo Hello World")!

Cheers,
Jan-Peter