Re: Array for system() call

[MZSanford]

When system() gets a scalar, it goes to the shell to execute the command. This means that you open a new shell instance (such a ksh), and run the program, including any redirection.

If system() gets an array, it instead does the fork() and then uses exec() to start the process. This by-passes the shell, so shell redirection does not work.

---

i had a memory leak once, and it ruined my favorite shirt.

[dmmiller2k]

To elaborate further, use this (note double quotes): system("@Call"); instead of this: system(@Call); to achieve the same effect as your first fragment.

And, BTW, you probably meant to do this:

    $Call[0] = "gawk";
    $Call[1] = "-f";
    $Call[2] = "test.gawk";
    $Call[3] = "test.file";
    $Call[4] = ">";
    $Call[5] = "out.file";

or (slightly more efficiently) this:

    @Call = ( "gawk",
              "-f",
              "test.gawk",
              "test.file",
              ">",
              "out.file" );

rather than your original code, which is assigning values to 1-element array slices, which are sublists -- NOT arrays! -- of references to the elements of the @Call array; needless to say, although it works, it is somewhat less efficient than either of the above approaches, and bad practice besides.

dmm

Give a man a fish and you feed him for a day ...
Teach the man to fish and you feed him for a lifetime

[blakem]

Here is an example of why using @arr[0] is just asking from trouble...

#!/usr/bin/perl -wT
use strict;

my @arr;

@arr[0] = localtime();
$arr[1] = localtime();

print "\$arr[0] = $arr[0]\n";
print "\$arr[1] = $arr[1]\n";

Any guesses about the output of this simple script? Select area below to find out.

=OUTPUT Scalar value @arr[0] better written as $arr[0] at ./arrayslice.pl line + 6. $arr[0] = 58 $arr[1] = Tue Oct 23 14:30:58 2001 5 points for anyone who expected $arr[0] to contain an integer. 20 points for anyone who knew it would contain the seconds value, *not* the number of elements in the list returned by localtime(). (10 points for anyone who coded up an example because they weren't sure... woohoo)

-Blake

[dmmiller2k]

Thanks for the example, blakem

dmm

You can give a man a fish and feed him for a day ...
Or, you can teach him to fish and feed him for a lifetime