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scheme system stdout and markup predicates

From: Jan-Peter Voigt
Subject: scheme system stdout and markup predicates
Date: Tue, 23 Aug 2011 13:32:38 +0200
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv: Gecko/20110617 Lightning/1.0b2 Thunderbird/3.1.11

Hello List,

I am using the scheme system command (on linux) to generate barcodes to include in the PDF:
\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))

% 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))
     (set! get-stencil (lambda (symbol)
               (assoc-get symbol cache)))
     (set! rem-stencil (lambda (symbol)
               (set! cache (assoc-set! cache symbol #f))
#(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)
#(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

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")!


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