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Full Discussion: Post Shell programming: Question about source a file and read data from the file
Top Forums Shell Programming and Scripting Post Shell programming: Question about source a file and read data from the file Post 302130302 by ccwq on Saturday 4th of August 2007 10:25:51 PM
Old 08-04-2007
Frequently Asked Questions for Assgn 3.
What does the .std_dbrc file contain?
Something like:

STD_DBROOT=${HOME}/class/2031/Assgn3/STD_DB

You do not submit this file, I will be using mine that will point to my std_db. But it should work with such a file, otherwise your program will not pass the tests.
Do we need the trailing slash (/) in the STD_DBROOT definition?
Your program should work even if there is no trailing slash. The idea is that two or more slashes are equivalent to one, so it is better if you have two slashes rather than none (disaster).
Can we invoke one of our scripts from within another script?
In principle yes, but it is far safer if you do not unless you know what you are doing. If I were you I would opt for cut and paste.
How do I use the .std_dbrc from within my own script?
You source it. Sourcing is normally just a dot (.).

. ${HOME}/.std_dbrc

If you create this file and it seems lost use

ls -a

Why can't I see my .std_dbrc with ls?
Because files that start with a dot are hidden in Unix/Linux. Use ls -a to see all your files in the current directory. I mostly use ls -ltr or ls -latr, to see the most recent (and thus most relevant files) last (the first one might have scrolled above the screen).
What does it mean to "source" a file?
The manual says:

. filename [arguments]
source filename [arguments]
Read and execute commands from filename in the current shell
environment and return the exit status of the last command exe-
cuted from filename. If filename does not contain a slash,
file names in PATH are used to find the directory containing
filename. The file searched for in PATH need not be exe-
cutable. When bash is not in posix mode, the current directory
is searched if no file is found in PATH. If the sourcepath
option to the shopt builtin command is turned off, the PATH is
not searched. If any arguments are supplied, they become the
positional parameters when filename is executed. Otherwise the
positional parameters are unchanged. The return status is the
status of the last command exited within the script (0 if no
commands are executed), and false if filename is not found or
cannot be read.

most of the details there are irrelevant to you, but the thing to keep in mind is that it executes commands from filename in the current shell environment.
Do I need to change the PATH environment variable for this assignment?
NO! You should not change the PATH. In general we do not play with PATH unless we know what we are doing.
 

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LEARN ABOUT CENTOS

dot

DOT(1P) 						     POSIX Programmer's Manual							   DOT(1P)

PROLOG

       This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
       ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME

       dot - execute commands in the current environment

SYNOPSIS

       . file

DESCRIPTION

       The shell shall execute commands from the file in the current environment.

       If file does not contain a slash, the shell shall use the search path specified by PATH to find the directory containing file. Unlike  nor-
       mal  command search, however, the file searched for by the dot utility need not be executable. If no readable file is found, a non-interac-
       tive shell shall abort; an interactive shell shall write a diagnostic message to standard error, but this condition shall not be considered
       a syntax error.

OPTIONS

       None.

OPERANDS

       See the DESCRIPTION.

STDIN

       Not used.

INPUT FILES

       See the DESCRIPTION.

ENVIRONMENT VARIABLES

       See the DESCRIPTION.

ASYNCHRONOUS EVENTS

       Default.

STDOUT

       Not used.

STDERR

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES

       None.

EXTENDED DESCRIPTION

       None.

EXIT STATUS

       Returns the value of the last command executed, or a zero exit status if no command is executed.

CONSEQUENCES OF ERRORS

       Default.

       The following sections are informative.

APPLICATION USAGE

       None.

EXAMPLES

	      cat foobar
	      foo=hello bar=world. foobar
	      echo $foo $bar
	      hello world

RATIONALE

       Some older implementations searched the current directory for the file, even if the value of PATH disallowed it.  This behavior was omitted
       from this volume of IEEE Std 1003.1-2001 due to concerns about introducing the susceptibility to trojan horses that the user might be  try-
       ing to avoid by leaving dot out of PATH.

       The  KornShell  version	of dot takes optional arguments that are set to the positional parameters. This is a valid extension that allows a
       dot script to behave identically to a function.

FUTURE DIRECTIONS

       None.

SEE ALSO

       Special Built-In Utilities

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and  the  original  IEEE
       and  The  Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained
       online at http://www.opengroup.org/unix/online.html .

IEEE
/The Open Group						       2003								   DOT(1P)
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