A wrapper around Systemd journalctl to print logs for the last n invocations of a unit

bash-completion.sh

# ============================================================================= #
# Copyright © 2025 Guiorgy                                                      #
#                                                                               #
# This program is free software: you can redistribute it and/or modify it under #
# the terms of the GNU General Public License as published by the Free Software #
# Foundation, either version 3 of the License, or (at your option) any later    #
# version.                                                                      #
#                                                                               #
# This program is distributed in the hope that it will be useful, but WITHOUT   #
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS #
# FOR A PARTICULAR PURPOSE.                                                     #
#                                                                               #
# You can see the full GNU General Public License at                            #
# <https://www.gnu.org/licenses/> for more details.                             #
# ============================================================================= #

_logsd() {
  # Load the journalctl completions if they aren't loaded yet
  if ! builtin declare -F _journalctl &>/dev/null; then
    if [[ -f /usr/share/bash-completion/completions/journalctl ]]; then
      builtin source /usr/share/bash-completion/completions/journalctl
    fi
  fi

  # Change the apparent command to 'journalctl --unit <input-to-complete>'
  COMP_WORDS=(journalctl --unit "${COMP_WORDS[COMP_CWORD]}")
  COMP_CWORD=2

  # Delegate completion to journalctl
  _journalctl
}

builtin complete -F _logsd logsd.sh

logsd.sh

#!/usr/bin/env bash

# ============================================================================= #
# Copyright © 2025 Guiorgy                                                      #
#                                                                               #
# This program is free software: you can redistribute it and/or modify it under #
# the terms of the GNU General Public License as published by the Free Software #
# Foundation, either version 3 of the License, or (at your option) any later    #
# version.                                                                      #
#                                                                               #
# This program is distributed in the hope that it will be useful, but WITHOUT   #
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS #
# FOR A PARTICULAR PURPOSE.                                                     #
#                                                                               #
# You can see the full GNU General Public License at                            #
# <https://www.gnu.org/licenses/> for more details.                             #
# ============================================================================= #

# Check systemd version
if command -v systemctl &>/dev/null; then
  SYSTEMD_VERSION=$(command systemctl --version | command head -n1 | command awk '{print $2}')
else
  builtin echo "Error: systemd/systemctl not found on this system." >&2
  builtin exit 1
fi

# Dependency Check
if ! command -v jq &>/dev/null; then
  builtin echo "Error: 'jq' is required for this script. Install it with: sudo apt install -y jq" >&2
  builtin exit 1
fi

# Print usage
usage() {
  builtin local name="$(command basename "$0")"
  command cat >&2 <<EOF

Print log entries from the systemd journal

Usage: $name [options] <unit-name> [count]

  unit-name      The name of the Systemd unit
  count          The number of invocations to print

Options:
  -f, --follow   Follow the journal
  -h, --help     Display this help message and exit

Examples:
  '$name nginx 1'   Current/Latest invocation only
  '$name nginx 3'   Everything from the last 3 invocation until now
  '$name -f nginx'  Follow current invocation
EOF
  builtin exit 1
}

# Flags and options
FOLLOW=0

# Parse flags and options
while [[ $# -gt 0 ]]; do
  case "$1" in
    -f|--follow)
      FOLLOW=1
    ;;
    -h|--help)
      usage
    ;;
    --)
      builtin shift
      builtin break
    ;;
    -*)
      builtin echo "Unrecognized option: '$1'" >&2
      usage
    ;;
    *)
      builtin break
    ;;
  esac

  builtin shift
done

# Positional arguments
UNIT="$1"; builtin shift
COUNT="${1:-1}"; builtin shift

# Argument validation
if [[ $# -ne 0 ]]; then
  builtin echo "Too many arguments: '$@'" >&2
  usage
fi
if [[ -z "$UNIT" ]]; then
  usage
fi
if [[ ! "$COUNT" =~ ^[0-9]+$ ]] || [[ "$COUNT" -le 0 ]]; then
  builtin echo "Error: Count must be a positive integer" >&2
  builtin exit 1
fi

# Get invocation IDs
INVOCATION_IDS=( \
  $( \
    command journalctl --unit="$UNIT" --output=json \
      | command jq --raw-output '._SYSTEMD_INVOCATION_ID' \
      | command grep --invert-match "null" \
      | command uniq
  ) \
)
INVOCATION_COUNT="${#INVOCATION_IDS[@]}"

# Validate invocations and count
if [[ "$INVOCATION_COUNT" -eq 0 ]]; then
  builtin echo "Warning: No log history found for unit: $UNIT"
  builtin exit 0
elif [[ "$INVOCATION_COUNT" -lt "$COUNT" ]]; then
  builtin echo "Warning: Only $INVOCATION_COUNT invocations found"
  COUNT="$INVOCATION_COUNT"
fi

# Get the timestamp of the first invocation to display
START_INDEX=$(( TOTAL_FOUND - COUNT ))
TARGET_ID="${INVOCATION_IDS[$START_INDEX]}"
START_TIME="$(command journalctl _SYSTEMD_INVOCATION_ID="$TARGET_ID" --output=json --lines='+1' | command jq --raw-output '.__REALTIME_TIMESTAMP')"

# Print information
START_TIME_FORMATTED="$(command date --date="@$(( START_TIME / 1000000 ))" '+%Y-%m-%d %H:%M:%S')"
builtin echo "--> Displaying logs for unit [$UNIT]"
builtin echo "--> Since invocation start: $START_TIME_FORMATTED (Invocation $COUNT of $INVOCATION_COUNT)"
builtin echo "--------------------------------------------------------------------------------"

# Additional arguments
ARGS=''
if [[ "$FOLLOW" -eq 1 ]]; then
  ARGS="$ARGS --follow"
fi

# Get logs
command journalctl $ARGS --unit="$UNIT" --since "$START_TIME_FORMATTED"

• Move the logsd.sh file into /usr/local/bin/logsd.sh.
• Rename and move the bash-completions.sh file into /usr/local/share/bash-completion/completions/logsd.sh.