1.8 Example Script

It is recommended that the application developer (or the compiler) package virtual machine code applications as shell scripts with the avram command line embedded in them. This style relieves the user of the need to remember the appropriate virtual machine options for invoking the application, which are always the same for a given application, or even to be aware of the virtual machine at all.

Here is a script that performs a similar operation to the standard Unix cat utility.

#!/bin/sh
#\
exec avram --force-text-input --default-to-stdin "$0" "$@"
sKYQNTP\

That is, it copies the contents of a file whose name is given on the command line to standard output, or copies standard input to standard output if no file name is given. This script can be marked executable (with chmod) and run by any user with the directory of the avram executable in his or her PATH environment variable, even if avram had to be installed in a non-standard directory such as ‘~/bin’.

The idea for this script is blatantly lifted from the wish manpage. The first line of the script invokes a shell to process what follows. The shell treats the second line as a comment and ignores it. Based on the third line, the shell invokes avram with the indicated options, the script itself as the next argument, and whatever command line parameters were initially supplied by the user as the remaining arguments. The rest of the script after that line is never processed by the shell.

When avram attempts to load the shell script as a virtual machine code file, which happens as a result of it being executed by the shell, it treats the first line as a comment and ignores it. It also treats the second line as a comment, but takes heed of the trailing backslash, which is interpreted as a comment continuation character. It therefore also treats the third line as a comment and ignores it. Starting with the fourth line, it reads the virtual code, which is in a binary data format encoded with printable characters, and evaluates it.

This document was generated on December 10, 2012 using texi2html 1.82.