comment on

Suppose I'm running a backticks or system command through a script that I've run from the command line. Is there anyway for me to stop that command midstream and have the script continue?

The application in question is a very simple MP3 shuffle player. What I want to be able to do is go to the next song while the current one is playing. Read more for the code.

#!/usr/bin/perl
use Data::Dumper;
open(PLAYLIST,"</somedir/myplaylist.lst");

my @songs;
while (<PLAYLIST>) {
   chomp();
   push(@songs,$_);
}

my $count = scalar(@songs);
print "We found $count songs\n";

while (scalar(@songs) > 0) {
   my $song_num = rand(scalar(@songs));
   print "*** Playing $songs[$song_num]\n";
   `mpg321 '$songs[$song_num]'`;
   splice(@songs,$song_num,1);
}
[download]

If it makes any difference, this is Perl 5.8.5 on SuSE Linux 9.2.

UPDATE: After taking my first steps into the larger world of fork/exec, I have something that works to the best that I can see. Read on for the new version. I'll probably eventually update it to not use ^C to get the next song so it's easier to stop the music. Thanks to RazorbladeBidet for gently pushing me to learn fork!

#!/usr/bin/perl

my $song_num;
my @songs;
my $pid;

sub catch_next {
   my $signame = shift;
   print "Going to next song!\n";
   my $count = kill(15,$pid);
}

sub reaper {
   $waitedpid = wait;
   $SIG{CHLD} = \&reaper;
}

open(PLAYLIST,"</somedir/myplaylist.lst");
while (<PLAYLIST>) {
   chomp();
   push(@songs,$_);
}

$SIG{INT} = \&catch_next;
$SIG{CHLD} = \&reaper;

my $count = scalar(@songs);
print "We found $count songs\n";

while (scalar(@songs) > 0) {
   $song_num = rand(scalar(@songs));
   my $song = $songs[$song_num];
   splice(@songs,$song_num,1);
   print "*** Playing $song\n";
   unless ($pid = fork) {
     exec("mpg321", "$song");
   }
   waitpid($pid,0);
}
[download]

UPDATE 2: Thanks to bluto for alerting me that I don't need a seperate SIGCHLD handler. The final code is below:

#!/usr/bin/perl

my $song_num;
my @songs;
my $pid;

sub catch_next {
   my $signame = shift;
   print "Going to next song!\n";
   my $count = kill(15,$pid);
}

open(PLAYLIST,"</somedir/myplaylist.lst");
while (<PLAYLIST>) {
   chomp();
   push(@songs,$_);
}

$SIG{INT} = \&catch_next;

my $count = scalar(@songs);
print "We found $count songs\n";

while (scalar(@songs) > 0) {
   $song_num = rand(scalar(@songs));
   my $song = $songs[$song_num];
   splice(@songs,$song_num,1);
   print "*** Playing $song\n";
   unless ($pid = fork) {
     exec("mpg321", "$song");
   }
   waitpid($pid,0);
}
[download]

In reply to Can I stop a backtick command but continue the script? by DentArthurDent

Are you posting in the right place? Check out Where do I post X? to know for sure.
Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
<code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>
Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
Want more info? How to link or How to display code and escape characters are good places to start.


Just another Perl shrine
	PerlMonks