Difference in commands


 
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# 1  
Old 06-22-2009
Difference in commands

Hello All, I have a question about the difference between two commands. I am using Korn and was told by the Unix admin that 'nohup <command> &'
equals 'nohup ./<command> &. That there is no difference betwewen the two. Is this true? Also, does the command './<command> &' provide a disconnect from the SSH session? I was under the impression that only nohup disconnects from the session. TIA.
# 2  
Old 06-22-2009
The ./ means execute a script or executable file in the current working directory. ./ls would only work if your current working directory were /usr/bin - ie.,
Code:
cd /somewhere
./ls

will generate an error unless there is an "ls" in the /somewhere directory

What you are seeing is the effect of the PATH variable as your sysadmin defined it - proabably in /etc/profile. It has nothing to with Korn shell per se. In other words, you PATH has a dot in it:
Code:
echo $PATH
.:/usr/bin/:/usr/sbin"

the .: thing means look in the current directory. It is a convenience, and a security risk as well. You could execute a file by mistake.
# 3  
Old 06-22-2009
Thanks! for the reply

What I am also wondering is...is './<command> &' tied to my Putty session? I know nohup disengages the session from the job, but I am wondering if the above string will do the same?
# 4  
Old 06-22-2009
./ means something in the current directory

nohup means don't "hang up" (i.e don't kill this when I leave) and it's not tied to any process (i.e. if you run nohup from the command line or a shell program and either of them die, or are killed or exited, the process will become owned by init... that which starts all processes. If init (process #1) dies then everything dies with it. So if you start something with nohup ... &, it will run in the background and continue to run after you log out.

& means run it in the background

As jim says the distinction between ./command and command is very important. Most sys admins won't have . in their path for the reasons he states.

Last edited by Scott; 06-22-2009 at 05:28 PM..
# 5  
Old 06-22-2009
Thanks!
 
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