/usr/bin/mpbi-split is in mpb 1.5-3.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 | #! /bin/bash
if test x"`echo $1 | egrep '^[0-9]*$'`" = x; then
    echo "Syntax: $0 <num-split> [mpb arguments...]" 1>&2
    exit 1
fi
tmpname=/tmp/mpb-split.$$.tmp # unique temporary filename
subprocesses="" # keep a list of the subprocess ids launched
# If a SIGINT or SIGHUP is received, kill subprocesses and delete temp. files:
trap 'echo "killing subprocesses: $subprocesses"; kill -9 $subprocesses; rm -f $tmpname.*; exit 1' 1 2
# Run num-split instances of mpb, each with a chunk of k-points, with
# the first chunk going to stdout and the rest going to temporary files
# to be output later.
/usr/bin/mpbi interactive?=false k-split-index=0 k-split-num=$* &
subprocesses="$subprocesses $!"
i=0
while test `expr $i \< $1` = 1; do
    /usr/bin/mpbi interactive?=false k-split-index=$i k-split-num=$* > $tmpname.$i &
    subprocesses="$subprocesses $!"
    i=`expr $i + 1`
done
# After all mpb processes have finished, concatenate their outputs in order.
wait
i=0
while test `expr $i \< $1` = 1; do
    cat $tmpname.$i
    rm -f $tmpname.$i
    i=`expr $i + 1`
done
 |