Write shell scripts and work faster on the command line

#!/bin/bash
# Show a short report about this machine
echo "Host:   $(hostname)"
echo "Kernel: $(uname -r)"
echo "Uptime: $(uptime -p)"
df -h /

#!/bin/bash
# Create one user for every name given on the command line
if [ $# -eq 0 ]; then
    echo "Usage: $0 NAME [NAME ...]" >&2
    exit 1
fi
for name in "$@"; do
    useradd "$name" && echo "created $name"
done

#!/bin/bash
# Exit 2 when the root file system is more than 90 % full
USED=$(df --output=pcent / | tail -1 | tr -dc '0-9')
if [ "$USED" -gt 90 ]; then
    echo "CRITICAL: / is ${USED}% full"
    exit 2
fi
echo "OK: / is ${USED}% full"
exit 0

#!/bin/bash
# Start, stop or show a service: svc.sh start|stop|status NAME
ACTION=$1
SERVICE=${2:?give a service name}
 
case "$ACTION" in
    start|stop|restart)
        systemctl "$ACTION" "$SERVICE" ;;
    status)
        if systemctl is-active --quiet "$SERVICE"; then
            echo "$SERVICE is running"
        elif systemctl is-failed --quiet "$SERVICE"; then
            echo "$SERVICE FAILED"
            exit 2
        else
            echo "$SERVICE is stopped"
        fi ;;
    *)
        echo "Usage: $0 start|stop|restart|status SERVICE" >&2
        exit 1 ;;
esac

#!/bin/bash
# Wait until a host answers ping (max. 60 tries), then go on
HOST=${1:?host name}
for try in $(seq 1 60); do
    if ping -c1 -W1 "$HOST" &> /dev/null; then
        echo "$HOST is up after $try tries"
        exit 0
    fi
    sleep 1
done
echo "$HOST did not answer" >&2
exit 1

#!/bin/bash
set -euo pipefail