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Top Forums Shell Programming and Scripting Understanding ampersand (&) usage in the command Post 302422338 by zaxxon on Tuesday 18th of May 2010 06:33:10 AM
Old 05-18-2010
You are right but I guess that this is just a typo and missing a 2nd adjacent & like marked bold here:
Code:
who && echo "Total number of users are `who|wc -l`"

This works then like if the 1st who is successful, the command following will be executed, maybe to check if "who" itself is available and working. Sending "who" in the background and then following up the rest of commands would make no sense.
 

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nice(1) 						      General Commands Manual							   nice(1)

Name
       nice, nohup - execute a command at a lower priority

Syntax
       nice [-number] command [arguments]

       nohup command [arguments]

Description
       The  command  executes command with low scheduling priority (Bourne Shell only).  If the number argument is present, the priority is incre-
       mented (higher numbers mean lower priorities) by that amount up to a limit of 20.  The default number is 10.

       The super-user may run commands with priority higher than normal by using a negative priority, for example, `--10'.

       The command executes command immune to hangup and terminate signals from the controlling terminal.  The priority is incremented by 5.   The
       command	should	be  invoked  from  the shell with an ampersand (&) in order to prevent it from responding to interrupts by or stealing the
       input from the next person who logs in on the same terminal.  The syntax of is also different.

Options
       -number		   Increments the priority by a specified number up to a limit of 20.  The default is 10.

Restrictions
       The and commands are particular to If you use then commands executed with an ampersand (&) are automatically immune to hangup signals while
       in the background.  There is a built-in command which provides immunity from terminate, but it does not redirect output to nohup.out.

       The  command  is built into with a slightly different syntax than described here.  The form ``nice +10'' nices to positive nice, and ``nice
       -10'' can be used by the superuser to give a process more of the processor.

Diagnostics
       The command returns the exit status of the subject command.

Files
       nohup.out standard output and standard error file under nohup

See Also
       csh(1), getpriority(2), renice(8)

																	   nice(1)
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