Passing an in memory scalar to an external command as an argument

Rodster001 has asked for the wisdom of the Perl Monks concerning the following question:

Forgive me if this is been asked before, I cannot find the answer and can't quite figure it out myself.

I have an in memory scalar and I want to pass that to an external program in a system command as an argument (instead of first writing a file and then calling the command).

For example:


my $mp3 = <binary contents of an mp3 file already in memory>;

system("/path/ffmpeg -i <want to pass $mp3 here>");
[download]

I know ffmpeg can take an input argument like this (if this helps):


cat my.mp3 | ffmpeg -i pipe:0
[download]

Thanks for the help

Comment on Passing an in memory scalar to an external command as an argument Select or Download Code

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Re: Passing an in memory scalar to an external command as an argument by pme (Monsignor) on Apr 08, 2015 at 18:54 UTC
This may help: `my $mp3 = <binary contents of an mp3 file already in memory>; $pid = open(PLAY, "\| ffmpeg -i pipe:0") or die "Couldn't fork: $!\n"; print PLAY $mp3; close(PLAY) or die "Couldn't close: $!\n";` [download]	[reply] [d/l]
Re^2: Passing an in memory scalar to an external command as an argument by LanX (Saint) on Apr 08, 2015 at 19:07 UTC
IIRC you'll better play safe and use `binmode` and/or `:raw` when passing binary content. see `PerlIO` Cheers Rolf _{(addicted to the Perl Programming Language and ☆☆☆☆ :) Je suis Charlie!}	[reply] [d/l]
Re^3: Passing an in memory scalar to an external command as an argument by Rodster001 (Pilgrim) on Apr 08, 2015 at 19:10 UTC
Thank you, BINMODE added to fh PLAY	[reply]
Re^2: Passing an in memory scalar to an external command as an argument by RonW (Parson) on Apr 08, 2015 at 20:55 UTC
I would suggest: `use IO::Pipe; my $pipe = IO::Pipe->new(); $pipe->writer(qw(ffmpeg -i pipe:0)); print $pipe $mp3;` [download] to avoid the shell being used to launch ffmpeg.	[reply] [d/l]
Re^3: Passing an in memory scalar to an external command as an argument by Rodster001 (Pilgrim) on Apr 08, 2015 at 22:38 UTC
I like that solution. But I need to capture stdout also (so I am actually using open2 for this). Can I write and read using IO::Pipe? The docs look like it is one or the other.	[reply]
Re^4: Passing an in memory scalar to an external command as an argument by RonW (Parson) on Apr 08, 2015 at 23:14 UTC
Re^2: Passing an in memory scalar to an external command as an argument by Rodster001 (Pilgrim) on Apr 08, 2015 at 19:08 UTC
That's what I was looking for, thank you sir	[reply]
Re: Passing an in memory scalar to an external command as an argument by Marshall (Canon) on Apr 09, 2015 at 03:47 UTC
In Perl, you can open an internal Perl variable with a file handle to read it like a file. Instead of a file name, you use a reference to the internal Perl variable name. You can also use this technique to print to an internal Perl variable. This is often a good technique to avoid the complications of creating temporary files. If the program "bombs", there are no extra files to clean up later. `open (MP3, '<' , \$mp3file) or die $!; binmode MP3; #more than one way to do this print MP3;` [download] yourprogram.pl > binaryfileconsumer;	[reply] [d/l]
Re: Passing an in memory scalar to an external command as an argument by Laurent_R (Canon) on Apr 08, 2015 at 19:09 UTC
And what about this: `system ("/path/ffmpeg -i $mp3");` [download] or possibly: `system ("cat my.mp3 \| ffmpeg -i pipe:0");` [download] Je suis Charlie.	[reply] [d/l] [select]
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