75 lines
2.2 KiB
C
75 lines
2.2 KiB
C
/*
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** Shell-script trampoline.
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** Copyright (c) 1994 by Olin Shivers.
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/*
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/* Unix #! shell scripts are not recursive. The interpreter you specify
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** on the #! line cannot itself be a shell script. This is a problem for
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** the Scheme shell, since it is implemented as a heap image executed
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** by the Scheme 48 vm. This means that users cannot write shell scripts
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** of the form:
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** #!/usr/local/bin/scsh -s
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** !#
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** ...Scheme code goes here...
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**
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** They must instead write:
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** #!/usr/local/lib/scsh/scshvm \
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** -o /usr/local/lib/scsh/scshvm -i /usr/local/lib/scsh/scsh.image -s
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** ...Scheme code goes here...
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**
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** This is gruesome and probably confusing to novices.
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**
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** What we do is have this tiny little stub program play the role of scsh.
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** It is compiled to a real Unix binary, but when it is executed, it simply
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** execs the scsh virtual machine, passing it an argv composed of
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** { "-o" "scshvm" "-i" "scsh.image"}
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** prepended to whatever argv it was given. Now you can write shell scripts
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** with
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** #!/usr/local/bin/scsh -s
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** triggers.
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**
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** There are two downsides to doing things this way.
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** 1. You pay an extra exec(2) at startup time.
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** And scsh starts up slow enough as it is.
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** 2. You cannot specify extra arguments for the vm this way. The most
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** important one you might want to specify is the heap size arg, -h.
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*/
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#include <errno.h>
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#include <unistd.h>
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#include <stdlib.h>
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#ifndef VM
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#define VM "/usr/local/lib/scsh/scshvm"
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#endif
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#ifndef IMAGE
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#define IMAGE "/usr/local/lib/scsh/scsh.image"
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#endif
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main(int argc, char *argv[])
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{
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char **ap, **aq, **newav;
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/* Insert "-o" VM "-i" IMAGE between argv[0] and argv[1]. */
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argc += 4; /* We're adding 4 new elts. */
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newav = (char **) malloc((argc+1) * sizeof(char*)); /* Alloc new argv. */
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if( !newav ) {
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perror(argv[0]);
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exit(1);
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}
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newav[0] = argv[0]; /* Install new header args. */
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newav[1] = "-o";
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newav[2] = VM;
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newav[3] = "-i";
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newav[4] = IMAGE;
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for(ap=&argv[0], aq=&newav[4]; *ap;) /* Copy over orignal argv */
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*++aq = *++ap; /* & the terminating NULL. */
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execv(VM, newav); /* Do it. */
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perror(argv[0]);
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exit(-1);
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}
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