#command cdx sort -m $TMP/aaa $TMP/bbb $TMP/ccc $TMP/ddd
#infile aaa
 CDX	foo
aaa
ccc
eee
ggg
#infile bbb
 CDX	foo
bbb
ddd
fff
hhh
#infile ccc
 CDX	foo
bbbb
dddd
ffff
hhhh
#infile ddd
 CDX	foo
aaaa
cccc
eeee
gggg
#stdout
 CDX	foo
aaa
aaaa
bbb
bbbb
ccc
cccc
ddd
dddd
eee
eeee
fff
ffff
ggg
gggg
hhh
hhhh