Bash shell script that runs a simple command (like ping) periodically and tests the results.

heartbeat.sh

#!/bin/bash
#
# Run a simple command every 15 seconds and report whether it passes
# or fails. It can be used to check for disconnected hosts (a
# heartbeat test).
#
# The minimum valid interval depends on the time it takes to execute
# the command.
#
# Usage:
#    $ ./heartbeat.sh CMD              # every 15 seconds, forever
#    $ INTERVAL=60 ./heartbeat.sh CMD  # every 60 seconds, forever
#    $ MAX=15 INTERVAL=60 ./heartbeat.sh CMD  # every 60 seconds, for 15 minutes
#
# Example:
#    $ ./heartbeat.sh ping -c 10 -i 0.5 my-test-host
#    $ ./heartbeat.sh ping -c 10 -i 0.5 my-test-host '>' /dev/null
#    $ INTERVAL=60 ./heartbeat.sh ping -c 10 -i 0.5 my-test-host '>' /dev/null
#    $ MAX=10 INTERVAL=60 ./heartbeat.sh ping -c 10 -i 0.5 my-test-host '>' /dev/null
#
: ${INTERVAL:=15}
: ${SLEEP:=0.5}
: ${MAX:=0}
CMD="$@"

# For systems like macs that use BSD date.
DATE=gdate
if ! $DATE --version >/dev/null 2>&1 ; then
    DATE=date
fi

# Print a bit of status information.
printf 'Cmd      : %s\n' "$CMD"
printf 'Interval : %d\n' $INTERVAL
printf 'Sleep    : %s\n' $SLEEP
printf 'Max      : %d\n' $MAX

if [ -z "$CMD" ] ; then
    echo -e "\033[31mERROR: A command must be specified!\033[0m"
    exit 1
fi
if ! $DATE --version >/dev/null 2>&1 ; then
    echo -e "\033[31mERROR:$LINENO: gnu compatible date program not found \033[0m"
fi

# Iterate forever, keep track of the number of times the test was
# performed in COUNT.
COUNT=0
START=0
while (( 1 )) ; do
    SECONDS=$($DATE +'%s')

    # Tests occur when the modulus is 0.
    if (( (SECONDS % INTERVAL) == 0 )) ; then
        (( COUNT++ ))

        echo -ne "\033[1m"
        printf '%5d %d ' $COUNT $MAX

        # Print the time elapsed first.
        # The first time through, print 00:00:00.
        CURR=$($DATE +'%s')
        (( START == 0 )) && START=$CURR
        ELAPSED=$(( CURR - START ))
        ELAPSED_STR=$($DATE -ud "@$ELAPSED" +'%H:%M:%S' | tr -d '\n')
        printf '%s ' $ELAPSED_STR

        # Print the current date/time with seconds resolution.
        CURR_DATE=$($DATE -Iseconds | tr -d '\n')

        # Print and run the command.
        echo -n "$CURR_DATE - $CMD"
        echo -e "\033[0m"

        # Use eval so that users can specify commands like:
        # ./tester/.sh ping -c 5 -i 0.5 HOST '>' /dev/null
        eval "$CMD"

        # Capture the exit status and report the current status.
        EXIT_CODE=$?
        if (( EXIT_CODE )) ; then
            echo -e "\033[31mSTATUS: FAILED $EXIT_CODE $COUNT $ELAPSED_STR $CURR_DATE\033[0m"
        else
            echo -e "\033[32mSTATUS: PASSED $EXIT_CODE $COUNT $ELAPSED_STR $CURR_DATE\033[0m"
        fi

        # Exit if the max threshold is exceeded.
        # If MAX < 1, then the loop never finishes.
        if (( COUNT >= MAX )) ; then
            break
        fi

        # Cross the modulus threshold to avoid running the command
        # more than once in the same time interval.
        SECONDS=$($DATE +'%s')
        while (( (SECONDS % INTERVAL) == 0 )) ; do
            sleep 0.1
            SECONDS=$($DATE +'%s')
        done
    fi

    # Pause for a bit to avoid continuous date testing.
    sleep $SLEEP
done