At the unix shell prompt, this is an example to make my test system (1234) say my call sign phonetically.
cat /var/lib/asterisk/sounds/this.gsm /var/lib/asterisk/sounds/is.gsm /var/lib/asterisk/sounds/phonetic/w_p.gsm /var/lib/asterisk/sounds/phonetic/b_p.gsm /var/lib/asterisk/sounds/digits/9.gsm /var/lib/asterisk/sounds/phonetic/u_p.gsm /var/lib/asterisk/sounds/phonetic/u_p.gsm /var/lib/asterisk/sounds/phonetic/s_p.gsm /var/lib/asterisk/sounds/repeater.gsm > /var/lib/asterisk/sounds/rpt/wb9uus-repeater.gsm
asterisk -vvvvr -x "rpt localplay 1234 /var/lib/asterisk/sounds/rpt/wb9uus-repeater"
This also works with ulaw files like this....
cat /var/lib/asterisk/sounds/this.ulaw /var/lib/asterisk/sounds/is.ulaw /var/lib/asterisk/sounds/phonetic/w_p.ulaw /var/lib/asterisk/sounds/phonetic/b_p.ulaw /var/lib/asterisk/sounds/digits/9.ulaw /var/lib/asterisk/sounds/phonetic/u_p.ulaw /var/lib/asterisk/sounds/phonetic/u_p.ulaw /var/lib/asterisk/sounds/phonetic/s_p.ulaw /var/lib/asterisk/sounds/repeater.ulaw > /var/lib/asterisk/sounds/rpt/wb9uus-repeater-u.ulaw
asterisk -vvvvr -x "rpt localplay 1234 /var/lib/asterisk/sounds/rpt/wb9uus-repeater-u"
I don't know if it works with other formats of audio files.
And yes, the full path is optional under some circumstances, depending on where the files are and what your current directory is, but is given here to avoid ambiguity.
Chuck WB9UUS