journalctl

#!/bin/bash

SYSTEMCTL_PY="systemctl3.py"

get_cmd(){
  local cmd="$1"
  command -v "$cmd" || printf "${0%/*}/$cmd"
}

SYSTEMCTL=$(get_cmd $SYSTEMCTL_PY)

unit=""
follow=false
lines=""
no_pager=false
system=false
user=false
root=""
x=false

out() { printf "$1 $2\n" "${@:3}"; }
error() { out "${0##*/}: error:" "$@"; } >&2
die() { error "$@"; exit 1; }

ignore_error() {
  "$@" 2>/dev/null
  return 0
}

usage() {
cat << EOF
usage: ${0##*/} [-h] -u unit [-f] [-n num] [--no-pager]
                  [--system] [--user] [--root path] [-x]
EOF
}

usage_verbose(){
usage
cat << EOF

options:
  -h, --help            show this help message and exit
  -u unit, --unit unit  Systemd unit to display
  -f, --follow          Follows the log
  -n num, --lines num   Num of lines to display
  --no-pager            Do not pipe through a pager
  --system              Show system units
  --user                Show user units
  --root path           Use subdirectory path
  -x                    Switch on verbose mode
EOF
}

die_arg(){
  local arg=$1
  shift
  if [ -z "$@" ] ;then
    local die0="$arg"
  else
    local die0="$@"
  fi

  case $arg in
    -*|"")
      usage
      die "${die1}${die0}${die2}"
      ;;
    *)
      ;;
    esac
}

expected_arg(){
  die1="argument "
  die2=": expected one argument"
  die_arg $@
}

required_arg(){
  die1="the following arguments are required: "
  die2=""
  die_arg $@
}

prepare(){
  [ ! -L "/tmp/run" ] && ln -sfr /tmp /tmp/run
  [ ! -x $SYSTEMCTL ] && die "${0##*/}: command not found: $SYSTEMCTL_PY"
  [ ! -x /usr/bin/python3 ] && die "${0##*/}: command not found: python3"
}

while [ $# -gt 0 ]; do
  case $1 in
    -h|--help)
      usage_verbose
      exit 0
      ;;
    -u|--unit)
      shift
      expected_arg $1 "-u/--unit"
      unit=$1
      ;;
    -f|--follow)
      follow=true
      ;;
    -n|--lines)
      shift
      lines=$1
      ;;
    --no-pager)
      no_pager=true
      ;;
    --system)
      system=true
      ;;
    --user)
      user=true
      ;;
    --root)
      shift
      root=$1
      ;;
    -x)
      x=true
      ;;
    *)
      error "argument $1: ignored explicit argument\'$1\'"
      shift
      ;;
  esac
  shift
done

required_arg "$unit" "-u/--unit"

cmd=("$SYSTEMCTL" "log" "$unit")
if [ "$follow" = true ]; then
  cmd+=("-f")
fi
if [ -n "$lines" ]; then
  cmd+=("-n" "$lines")
fi
if [ "$no_pager" = true ]; then
  cmd+=("--no-pager")
fi
if [ "$system" = true ]; then
  cmd+=("--system")
elif [ "$user" = true ]; then
  cmd+=("--user")
fi
if [ -n "$root" ]; then
  cmd+=("--root" "$root")
fi
if [ "$x" = true ]; then
  cmd+=("-vvv")
fi

prepare
[ -r "/var/log/journal/$unit.log" ] || \
[ -r "/var/log/journal/$unit.service.log" ] && \
ignore_error exec "${cmd[@]}"
exec "${cmd[@]}"