This project is available at https://github.com/danieloneill/alsalist.

A simple 42 line utility for Linux/ALSA to list MIDI devices in a format suitable for automation. (eg: bash, udev)

Developed in C using only asoundlib, this utility scans connected devices and provides their addresses and names. It is intended to be used with MIDI adapters to patch inputs with outputs automatically.

As it is only 42 lines, the entirety is provided below:

#include <asoundlib.h>

int main(int argc, char **argv)
{
        snd_seq_t *seq;
        snd_seq_port_info_t *pinfo;
        snd_seq_client_info_t *cinfo;

        int ret = snd_seq_open(&seq, "default", SND_SEQ_OPEN_INPUT, 0);
        if( ret != 0 ) return -1;

        snd_seq_set_client_name(seq, "alsaconnector");

        ret = snd_seq_client_info_malloc(&cinfo);
        if( ret != 0 ) return -2;

        ret = snd_seq_port_info_malloc(&pinfo);
        if( ret != 0 ) return -3;

        snd_seq_client_info_set_client(cinfo, -1);
        while (snd_seq_query_next_client(seq, cinfo) >= 0) {
                int cid = snd_seq_client_info_get_client(cinfo);
                if( cid == snd_seq_client_id( seq ) ) continue; // don't need to look at ourself..

                const char *cname = snd_seq_client_info_get_name(cinfo);
                snd_seq_port_info_set_client(pinfo, cid);
                int nports = snd_seq_client_info_get_num_ports(cinfo);

                snd_seq_port_info_set_port(pinfo, -1);
                while( snd_seq_query_next_port(seq, pinfo) >= 0 )
                {
                        int pid = snd_seq_port_info_get_port(pinfo);
                        const char *pname = snd_seq_port_info_get_name(pinfo);
                        printf("%d:%d %s : %s\n", cid, pid, cname, pname);
                }
        }

        snd_seq_port_info_free(pinfo);
        snd_seq_client_info_free(cinfo);
        snd_seq_close( seq );
        return 0;
}
        

Build (on Linux) with:

gcc -o alsalist alsalist.c `pkg-config --cflags --libs alsa`