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13.7 Running Image Files

You can invoke Gforth with an image file image instead of the default gforth.fi with the -i flag (see Invoking Gforth):

     gforth -i image

If your operating system supports starting scripts with a line of the form #! ..., you just have to type the image file name to start Gforth with this image file (note that the file extension .fi is just a convention). I.e., to run Gforth with the image file image, you can just type image instead of gforth -i image. This works because every .fi file starts with a line of this format:

     #! /usr/local/bin/gforth-0.4.0 -i

The file and pathname for the Gforth engine specified on this line is the specific Gforth executable that it was built against; i.e. the value of the environment variable GFORTH at the time that gforthmi was executed.

You can make use of the same shell capability to make a Forth source file into an executable. For example, if you place this text in a file:

     #! /usr/local/bin/gforth
     
     ." Hello, world" CR
     bye

and then make the file executable (chmod +x in Unix), you can run it directly from the command line. The sequence #! is used in two ways; firstly, it is recognised as a “magic sequence” by the operating system1 secondly it is treated as a comment character by Gforth. Because of the second usage, a space is required between #! and the path to the executable (moreover, some Unixes require the sequence #! /).

Most Unix systems (including Linux) support exactly one option after the binary name. If that is not enough, you can use the following trick:

     #! /bin/sh
     : ## ; 0 [if]
     exec gforth -m 10M -d 1M $0 "$@"
     [then]
     ." Hello, world" cr
     bye \ caution: this prevents (further) processing of "$@"

First this script is interpreted as shell script, which treats the first two lines as (mostly) comments, then performs the third line, which invokes gforth with this script ($0) as parameter and its parameters as additional parameters ("$@"). Then this script is interpreted as Forth script, which first defines a colon definition ##, then ignores everything up to [then] and finally processes the following Forth code. You can also use

     #0 [if]

in the second line, but this works only in Gforth-0.7.0 and later.

The gforthmi approach is the fastest one, the shell-based one is slowest (needs to start an additional shell). An additional advantage of the shell approach is that it is unnecessary to know where the Gforth binary resides, as long as it is in the $PATH.

#!              gforth       “hash-bang”

An alias for \


Fußnoten

[1] The Unix kernel actually recognises two types of files: executable files and files of data, where the data is processed by an interpreter that is specified on the “interpreter line” – the first line of the file, starting with the sequence #!. There may be a small limit (e.g., 32) on the number of characters that may be specified on the interpreter line.