wallsleep -- like sleep, but uses wall time not process time

wallsleep.sh

#!/bin/sh

# sleeps for $1 seconds based on wall time, not CPU time

set -e

# known-good with:
# - GNU date (Ubuntu 14.04.3 LTS)
# - Darwin date (OS X 10.11.4)

wallsleep() {
    then=$(( $1 + $(date +%s) ))
    while [ "$(date +%s)" -lt $then ]; do sleep 1; done
}

if [ "$#" -ne 1 ]; then
    echo "usage: $(basename $0) seconds" 1>&2
    exit 1
fi

wallsleep "$@"