Understanding Logic and Flow better Post: 302330369

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Top Forums Shell Programming and Scripting Understanding Logic and Flow better Post 302330369 by otheus on Wednesday 1st of July 2009 04:07:19 AM

07-01-2009

Registered User

Quote:

"Does anybody have some tips on understanding and mapping out the logic and flow of scripts"

First, you're rambling; get some sleep (if you can after 3 pots of coffee).

Second, "scripts" are usually executed in order the lines appear in the program, with the exception of things like loops. SH and derivatives (bash, zsh) handle functions, and these functions need to be defined before they are invoked. Other than that, it's pretty straight-forward.

*Sigh* then again, I've been coding since I was 10.

Third: You must understand Binary Logic (aka, Boolean Logic). The keys are understanding the basic operators: OR, AND, NOT. If you don't understand these correctly, you'll have a hard time. In most modern languages, including shell scripting, perl, and C, the operands can be expressions which means in the case of shell scripting, a program that returns an exit code.

So fourth, you have to understand that programs return exit codes. If the exit code is numerically 0, that means true. (0 for true is known sometimes as "negative logic").

If you are visually oriented, this tutorial might help.
I googled around and found this video which might help: YouTube - Prelude to Computer Science - 6: Binary Logic and YouTube - Prelude to Computer Science - 7: Logic Gates

otheus

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LEARN ABOUT CENTOS

sg

SG(1)								   User Commands							     SG(1)

NAME

       sg - execute command as different group ID

SYNOPSIS

       sg [-] [group [-c ] command]

DESCRIPTION

       The sg command works similar to newgrp but accepts a command. The command will be executed with the /bin/sh shell. With most shells you may
       run sg from, you need to enclose multi-word commands in quotes. Another difference between newgrp and sg is that some shells treat newgrp
       specially, replacing themselves with a new instance of a shell that newgrp creates. This doesn't happen with sg, so upon exit from a sg
       command you are returned to your previous group ID.

CONFIGURATION

       The following configuration variables in /etc/login.defs change the behavior of this tool:

       SYSLOG_SG_ENAB (boolean)
	   Enable "syslog" logging of sg activity.

FILES

       /etc/passwd
	   User account information.

       /etc/shadow
	   Secure user account information.

       /etc/group
	   Group account information.

       /etc/gshadow
	   Secure group account information.

SEE ALSO

       id(1), login(1), newgrp(1), su(1), gpasswd(1), group(5), gshadow(5).

shadow-utils 4.1.5.1						    05/25/2012								     SG(1)