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Full Discussion: Looping through input/output
Top Forums UNIX for Beginners Questions & Answers Looping through input/output Post 302979923 by Don Cragun on Sunday 21st of August 2016 04:21:08 PM
Old 08-21-2016
Hi bakunin,
Sorry to disagree with you here, but back in the early UNIX days on the PDP-11, the magic number determining the type of executable was 2 bytes (16-bits) not 4 bytes. And, when #! was added to the magic numbers recognized by the kernel, a leading space was not allowed. Since then, some kernels allow one or more leading spaces, some kernels allow a single option (e.g., #!/bin/sh -xv), and some kernels may even invoke a shell to evaluate the entire first line starting from the 3rd character as a shell command with the rest of the file as input (although I am not aware of any of these systems that are still produced today).

I believe that the PWB UNIX Systems I used when I was learning the OS treated:
Code:
#! /bin/sh

as a request to run the sh utility in the bin directory in the <space> directory, but I don't remember if it interpreted it as / /bin/sh or as ./ /bin/sh.
 

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GZEXE(1)                                                      General Commands Manual                                                     GZEXE(1)

NAME
gzexe - compress executable files in place SYNOPSIS
gzexe name ... DESCRIPTION
The gzexe utility allows you to compress executables in place and have them automatically uncompress and execute when you run them (at a penalty in performance). For example if you execute ``gzexe /usr/bin/gdb'' it will create the following two files: -rwxr-xr-x 1 root root 1026675 Jun 7 13:53 /usr/bin/gdb -rwxr-xr-x 1 root root 2304524 May 30 13:02 /usr/bin/gdb~ /usr/bin/gdb~ is the original file and /usr/bin/gdb is the self-uncompressing executable file. You can remove /usr/bin/gdb~ once you are sure that /usr/bin/gdb works properly. This utility is most useful on systems with very small disks. OPTIONS
-d Decompress the given executables instead of compressing them. SEE ALSO
gzip(1), znew(1), zmore(1), zcmp(1), zforce(1) CAVEATS
The compressed executable is a shell script. This may create some security holes. In particular, the compressed executable relies on the PATH environment variable to find gzip and some standard utilities (basename, chmod, ln, mkdir, mktemp, rm, sleep, and tail). BUGS
gzexe attempts to retain the original file attributes on the compressed executable, but you may have to fix them manually in some cases, using chmod or chown. GZEXE(1)
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