Книга: Fedora™ Unleashed, 2008 edition

Access to the Shell

Access to the Shell

Perl can perform any process you might ordinarily perform if you type commands to the shell through the `` syntax. For example, the code in Listing 25.4 prints a directory listing.

$curr_dir = `pwd`;
@listing = `ls -al`;
print "Listing for $curr_dirn";
foreach $file (@listing) {
 print "$file";
}

You can also use the Shell module to access the shell. Shell is one of the standard modules that comes with Perl; it allows creation and use of a shell-like command line. Look at the following code for an example:

use Shell qw(cp);
cp ("/home/httpd/logs/access.log", "/tmp/httpd.log");

This code almost looks as if it is importing the command-line functions directly into Perl. Although that is not really happening, you can pretend that the code is similar to a command line and use this approach in your Perl programs.

A third method of accessing the shell is via the system function call:

$rc = 0xffff & system('cp /home/httpd/logs/access.log /tmp/httpd.log');
if ($rc == 0) {
 print "system cp succeeded n";
} else {
 print "system cp failed $rcn";
}

The call can also be used with the or die clause:

system('cp /home/httpd/logs/access.log /tmp/httpd.log') == 0
 or die "system cp failed: $?"

However, you can't capture the output of a command executed through the system function.

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