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Top Forums UNIX for Dummies Questions & Answers taking a look at the code for some commands Post 302337120 by Corona688 on Thursday 23rd of July 2009 12:25:53 PM
Old 07-23-2009
Most common UNIX commands are written in C, which is converted from source code to executable code in several steps.

many source files(.c) ---compile---> many object files(.o) ---link---> one executable file

Compilation turns seperate .c files into machine code, stored in object files, usually .o. If anything in a.c calls a function in b.c, that will not be incorporated into a.o, the objects are all separate from each other. Because of this a third step is needed to join them all together: Linking. This resolves where everything the seperate object files needs comes from, be it other objects or external libraries, and writes it out in a form your computer can load and execute natively, the executable file.

So any changes in the source mean the respective object file needs to be recompiled, and any new object files mean the executable has to be relinked. Only the source code is human-readable.
 

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OPEN(1) 							     Linux 1.x								   OPEN(1)

NAME
open - start a program on a new virtual terminal (VT). SYNOPSIS
open [-c vtnumber] [-s] [-u] [-l] [-v] [--] command command_options DESCRIPTION
open will find the first available VT, and run on it the given command with the given command options, standard input, output and error are directed to that terminal. The current search path ($PATH) is used to find the requested command. If no command is specified then the envi- ronment variable $SHELL is used. OPTIONS -c vtnumber Use the given VT number and not the first available. Note you must have write access to the supplied VT for this to work. -s Switch to the new VT when starting the command. The VT of the new command will be made the new current VT. -u Figure out the owner of the current VT, and run login as that user. Suitable to be called by init. Shouldn't be used with -c or -l. -l Make the command a login shell. A - is prepended to the name of the command to be executed. -v Be a bit more verbose. -w wait for command to complete. If -w and -s are used together then open will switch back to the controlling terminal when the command completes. -- end of options to open. NOTE
If open is compiled with a POSIX (Gnu) getopt() and you wish to set options to the command to be run, then you must supply the end of options -- flag before the command. EXAMPLES
open can be used to start a shell on the next free VT, by using the command: open bash To start the shell as a login shell, use: open -l bash To get a long listing you must supply the -- separator: open -- ls -l SEE ALSO
login(1), doshell(8), switchto(1). AUTHOR
Jon Tombs <jon@gtex02.us.es or jon@robots.ox.ac.uk> -w idea from "sam". 19 Jul 1996 V1.4 OPEN(1)

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