[SOLVED] output of the command

ankitm · 10-19-2011, 06:57 AM

fname=try.tmp.$$
ps -C a.out -o pid= | grep -v $$ > ${fname} 2 > /dev/null

Could anyone tell the output of this command
what does 2 here signifies as there are two redirection statements

When I executed it in commna dline it showed Ambigous redirection.
However when "I executed it in a script it worked but I am unable to figure out what this actually does

Please help.....

aav · 10-19-2011, 07:49 AM

2 is for stderr (standard error).

jrhorn424 · 10-19-2011, 08:08 AM

Quote:

Originally Posted by aav

2 is for stderr (standard error).

These numbers are called file descriptors, and 1 is for standard output. 0 is for standard input. Have a look at the bash manual and search for "file descriptor" and "redirection" for more information.

goossen · 10-19-2011, 08:09 AM

From man ps:

Quote:

Print only the process IDs of syslogd:
ps -C syslogd -o pid=

And "grep -v" means print the not matching lines.

ankitm · 10-19-2011, 08:36 AM

Thanks for help

This means this should store the pid of a.out in the file ,but on executing it , i checked that the file was empty .

I have a process named a.out created and running in the background.

So what might be the reason fot it?