Check out perlop and the ` backtick or qx operator. These run a command and capture the output.

my @return = `ls -l`;
[download]

This is also a FAQ. Try running 'perldoc -q capture' from your commandline and you will see this FAQ.

Perldoc has many useful features besides the '-q' for FAQ keywords, you can find them by just running 'perldoc'

open(DD, "/bin/dd $dd_options |");
while ($line = <DD>) {
    # do whatever with the output of dd, one line at a time
    ...
}
[download]

Hi,
Is there any difference between the backticks and the process open
which you have just demonstrated?
I mean, does perl internally implement it differently?
For eg. A backtick may be passed to the shell directly
while the open(as above) may be implemented using popen,
which involves creating a pipe, forking, and invoking
the shell.
Or does perl just execute the command and then provide you
with a line by line output as you read it.

Thanx
--
arc_of_descent

> Is there any difference between the backticks and the process open which you have just demonstrated?
A quick glance over the perlipc manpage reveals they that are similar in intent. They both fork and execute the process, but open() ...

... gives you finer control of the whole process, letting you to kill off the child process early if you'd like.

So you might use open() if you want to exit from the process early in order to avoid unnecessary overhead.
HTH

broquaint

As petral pointed out, dd outputs its status messages on STDERR, not on STDOUT, but open and backticks only capture STDOUT. You can get around this by redirecting STDERR into the STDOUT file handle; the syntax is the same as on the shell command line, because Perl calls the Bourne shell to set up the redirection:
dd if=infile of=outfile 2>&1 Example Perl code:

my @r = `dd if=infile of=outfile 2>&1`;
foreach (@r) {
    chomp;
    print "***$_***\n";
}
[download]

***0+1 records in***
***0+1 records out***
[download]

Note that this only works correctly when you use the of parameter of dd. If you redirect STDOUT using the shell instead, then Perl will not see the status messages, because they get embedded somewhere in the output file. For example:

# BAD CODE
my @r = `dd if=infile >outfile 2>&1`;
[download]

I wrote this to give a dd specific example. In the perlfaq pointer (How can I capture STDERR from an external command?) that grep gave earlier, all the permutations of STDOUT vs. STDERR and open vs. backticks are discussed.