Basic Perl for homework - perl

Question

I am in school and in a network programming class. I have no Perl experience at all. Our assignment is as follows.
Write a short program that uses the backticks `` function to run the external command ps -aux to list all currently running processes owned by the user, whose username is given as a command line argument.
Hint:
$ARGV[0] or die "without a username given\n";
my $.... = $ARGV[0];
my #ps = `ps -axu`;
foreach my $..... (#ps) {
print $line if …../;
}
I have changed the code to this:
#!/usr/local/bin/perl -w
use strict;
use warnings;
my $line;
$ARGV[0] or die "without a username given\n";
my $test = $ARGV[0];
my #ps = `ps -axu`;
foreach my $test (#ps) {
print $line if ...../;
}
however, i keep getting this error:
syntax error at C:\Perl\W4A2new.pl line 10, near "if ..."
Search pattern not terminated at C:\Perl\W4A2new.pl line 10.
Can anyone help me out??? Please. thank you.

Answer 1

The ps command is usually invoked like ps aux (without leading minus).
Specifying a user name in the ps argument has no effect I can see
Using backticks is convenient, but could be considered bad style.
The first column of the ps aux output can contain a numeric user ID.
We can use /etc/passwd to translate between user IDs and user names.
Here is code that prints out all ps lines that start with a given string:
#!/usr/bin/perl
use strict; use warnings;
print grep /^\Q$ARGV[0]\E/, `ps aux`;
That last line could be written verbose:
my #temp;
for (`ps aux`) {
push #temp, $_ if /^\Q$ARGV[0]\E/;
}
print #temp;
That script would be invoked like perl script.pl root or perl script.pl 1000.
Now as I said, we can translate between usernames and user IDs. Also, we can treat the ps output as the column data it is. The columns are
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
We can access these cols by my #cols = split ' ', $line, 11. We have to specify a maximum number of cols as the command may contain whitespaces. If the user contains only digit characters, we translate to the corresponding name in /etc/passwd:
#!/usr/bin/perl
use strict; use warnings;
my $username = $ARGV[0] or die <<"END_USAGE";
USAGE: perl $0 USERNAME
USERNAME -- the full username you want ps output for.
END_USAGE
my %id_2_name = do {
open my $passwd, "<", "/etc/passwd" or die "Can't open passwords: $!";
map { (split /:/)[2,0] } <$passwd>;
};
open my $ps, "-|", "ps", "aux" or die "Can't open ps command: $!";
while(<$ps>) {
my #cols = split ' ', $_, 11;
$cols[0] = $id_2_name{$cols[0]} unless $cols[0] =~ /[^0-9]/;
print join " ", #cols if $cols[0] eq $username;
}

Answer 2

#!/usr/local/bin/perl -w
use strict;
use warnings;
my $username = $ARGV[0] or die "without a username given\n";
my #ps = `ps -axu $username`;
foreach my $line (#ps) {
print $line, "\n";
}
you must execute this script in this way (assuming the script name is myscript.pl):
perl myscript.pl your_operating_system_user_name