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Full Discussion: Help with simple program. (beginner)
Top Forums Shell Programming and Scripting Help with simple program. (beginner) Post 302513964 by Corona688 on Thursday 14th of April 2011 12:04:35 PM
Old 04-14-2011
A good start but there's a few things to figure out here:
Code:
if [ $ cat /etc/passwd | cut -d: -f1= "$username" ]

You don't put programs inside [ ] like that, you can just put them there raw.

That is also a useless use of cat, whenever you have cat stuff | program it's better to do program < stuff.

There's a trick you can do with grep to check for a user in the password file:

Code:
if grep -q "^${username}:" /etc/passwd
then
...

The ^ makes it look at the beginning of the line, so it looks for ${username}: at the beginning of any line in /etc/passwd. The -q tells it not to print anything, just return true or false as usual.

Code:
while [ $(who | grep $username) != 0 ]

This is a useless use of backticks (since the $(stuff) syntax is a special form of backticks). You don't check a return value in that fashion, either -- what that statement would actually end up doing is checking the string output of who | grep $username.

How you check a return value is like:

Code:
# there really are 'true' and 'false' programs, so go ahead and
# try these statements
if true
then
       echo "true returns true"
fi

if ! false
then
        echo "false returns false"
fi

So how about:
Code:
while who | grep -q "${username}"
do
...

Code:
exit 1

1 means error, by returning 1 you're telling whatever ran it that your program failed. Use 'exit 0' to show that your program ran successfully.
 

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LEARN ABOUT PHP

upsrw

UPSRW(8)							    NUT Manual								  UPSRW(8)

NAME

       upsrw - UPS variable administration tool

SYNOPSIS

       upsrw ups

       upsrw -h

       upsrw -s variable [-u username] [-p password] ups

DESCRIPTION

       upsrw allows you to view and change the read/write variables inside your UPS. It sends commands via the server upsd(8) to your driver,
       which configures the hardware for you.

       The list of variables that allow you to change their values is based on the capabilities of your UPS equipment. Not all models support this
       feature. Typically, cheaper hardware does not support any of them. Run upsrw with a UPS identifier to see what will work for you.

OPTIONS

       -h
	   Display the help message.

       -s variable
	   Specify the variable to be changed inside the UPS. For unattended mode such as in shell scripts, use the format VAR=VALUE to specify
	   both the variable and the value, for example:

	       -s input.transfer.high=129

	   Without this argument, upsrw will just display the list of the variables and their possible values.

	   Some variables are strings, and can be set to any value within the length limit. Others are enumerated types and can only be set to one
	   of those values. Others may be within an allowed range of values. Refer to the list to know what's available in your hardware.

       -u username
	   Set the NUT username for the connection to the server. This is optional, and you will be prompted for this when using the -s option if
	   you don't specify -u on the command line. NUT usernames are defined in upsd.users(5), and are not linked to system usernames.

       -p password
	   Set the password to authenticate to the server. This is also optional like -u, and you will be prompted for it if necessary.

       ups
	   View or change the settings on this UPS. The format for this option is upsname[@hostname[:port]]. The default hostname is "localhost".

UNATTENDED MODE

       If you run this program inside a shell script or similar to set variables, you will need to specify all of the information on the command
       line. This means using -s VAR=VALUE, -u and -p. Otherwise it will put up a prompt and your program will hang.

       This is not necessary when displaying the list, as the username and password are not required for read-only mode.

DIAGNOSTICS

       upsrw can't set variables on your UPS unless you provide a valid username and password. If you get "access denied" errors, make sure that
       your upsd.users(5) has an entry for you, and that the username you are using has permissions to SET variables.

HISTORY

       This program used to be called upsct2, which was ambiguous and confusing.

SEE ALSO

       upsd(8), upscmd(8)

   Internet resources:
       The NUT (Network UPS Tools) home page: http://www.networkupstools.org/

Network UPS Tools						    05/24/2012								  UPSRW(8)
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