aria2 is a nifty command line download manager — similar to, but much more powerful than — wget.

This post is not a review of aria2 (maybe I'll do one some day), rather it focuses on one of its features which has bugged me for a while.

aria2 can — among other things — be used to download torrents. You just pass a torrent file or a URL pointing to one, to aria2c (the actual name of the binary) and it starts downloading the torrent contents.

But, I use rtorrent to download torrents, and just want to download the .torrent file with aria2. But, since aria2 simply starts downloading the torrent contents instead of just the file, I was forced to use wget for downloading the file.

Even after searching all over the internet, I couldn't find a way to do so with aria2.

Finally, found the solution right under my nose. It was present right there in the man page of aria2.

From man aria2c:

--follow-torrent=true|false|mem
        If true or mem is specified, when a file whose suffix is
        .torrent or content type is application/x-bittorrent
        is downloaded, aria2 parses it as a torrent file and
        downloads files mentioned in it.  If mem is specified, a
        torrent file is not written to the disk, but is just kept
        in memory. If false is specified, the action mentioned
        above is not taken.  Default: true

Unfortunately, the wording is not so clear, maybe I'll offer a fix to the author.

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Update - 12 June 2013: My fix was accepted by aria2's author. The man page should now read:

If false is specified, the .torrent file is downloaded to the
disk, but is not parsed as a torrent and its contents are not
downloaded.

The following text should still be helpful for those who don't like reading man pages.

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Anyway, to download a .torrent file, just use the above switch with the false option, for example:

$ aria2c --follow-torrent=false http://cdimage.debian.org/debian-cd/7.0.0/multi-arch/bt-cd/debian-7.0.0-amd64-i386-netinst.iso.torrent

To avoid passing the switch regularly, just put:

follow-torrent=false

in ~/.aria2/aria2.conf.

Note: Options present in the configuration file can be overridden by the command line switches.