Running system commands

[vincente13]

Hi all


Im using
system("ps -fu $USER | grep $INSTANCE | grep -v grep | awk {print $2} "
)

$USER and $INSTANCE are variables from my perl program

However $2 is suppose to be from the pipe output.
Somehow Perl is interpreting $2 to be some variables from the program
itself

So how can differentiate the program variables and system variables?

Appreciate any help

 

[vincente13]

It seems like i can do this
system("ps -fu $USER | grep $INSTANCE | grep -v grep | awk {print \$2}
")

Put in a backslash

 

[Jürgen Exner]

system("ps -fu $USER | grep $INSTANCE | grep -v grep | awk {print $2}
" )

Well, the first question would be why are you forking out an external grep
with all the process overhead involved instead of simply using Perl's
buildin grep() command. And the same for awk. There is nothing that awk can
do that Perl can't do.

$USER and $INSTANCE are variables from my perl program

However $2 is suppose to be from the pipe output.

Actually now. $2 is supposed to be passed literally as a command line
argument to awk without any interpolation whatsoever.

Somehow Perl is interpreting $2 to be some variables from the program
itself

Of course. It is the second group that was matched successfully by the most
recent regular expression.

So how can differentiate the program variables and system variables?

You don't. $2 is not a 'system' variable, whatever that is supposed to mean.
You want to pass the literal text '$2' to awk. And that's simply done by
escaping the $ sign with a backslash.

jue

 

[John W. Krahn]

Im using
system("ps -fu $USER | grep $INSTANCE | grep -v grep | awk {print $2} "
)

$USER and $INSTANCE are variables from my perl program

However $2 is suppose to be from the pipe output.
Somehow Perl is interpreting $2 to be some variables from the program
itself

So how can differentiate the program variables and system variables?

Try it like this instead:

print
map { ( split )[ 1 ], "\n" }
grep /\Q$INSTANCE/,
`ps -fu $USER`;



John

 

[Ted Zlatanov]

It seems like i can do this
system("ps -fu $USER | grep $INSTANCE | grep -v grep | awk {print \$2}
")

Just use sprintf! It's clearer, too.

system sprintf('ps -fu %s | grep %s | grep -v grep | awk {print $2}',
$USER,
$INSTANCE);

Of course, what you are doing is not portable, probably wrong, and
better done with Proc:rocessTable

Ted