boot-diff

#!/usr/bin/env bash

#USAGE: boot-diff [from-boot] [to-boot] [journalctl-args]
#
#EXAMPLE:
#  # Show full-log diff between previous boot and current.
#  boot-diff
#  # or equivalently
#  boot-diff 1 0
#
#  # Show full-log diff between two boots ago and previous boot.
#  boot-diff 2 1
#
#  # Show diff of warning or higher priority messages between current and
#  # previous boot.
#  boot-diff --priority=warning
#
#
#DESCRIPTION:
#  Presents a side-by-side comparison of log messages between two different
#  boots of the system. Defaults to comparing current boot and previous boot.
#  Works using journalctl, so on systems using systemd.
#
#  Author: Stuart A. Knock
#  Originally Written: 2017-07-10
#  https://github.com/stuart-knock/bash-tools
#

# Use the header as a basic help message.
[[ "$1" =~ ^('-h'|'--help')$ ]] && { head -n $((LINENO-2)) "${BASH_SOURCE[0]}" | tail -n +2; exit 0 ; }

# Set some variables for message formatting.
declare -r ERROR='\e[1;31mERROR:\e[0m %s\n' # Bold Red error message format.

# Parse input args
JCTL_ARGS=()
while (( $# > 0 )); do
  arg="$1"
  if [[ "${arg:0:1}" = '-' ]]; then
    JCTL_ARGS+=("$arg")
    shift #Past argument
  elif [[ -z "$from_boot" ]]; then
    from_boot="$arg"
    shift #Past argument
  elif [[ -z "$to_boot" ]]; then
    to_boot="$arg"
    shift #Past argument
  else
    printf "$ERROR" "Could not parse command line arg '${arg}'."
    exit 1
  fi
done

# Default boots to compare if none provided
[[ -z "$from_boot" ]] && from_boot='1'
[[ -z "$to_boot" ]] && to_boot='0'

# Get current terminal width.
display_width="$(tput cols)"
# (( display_width < 200 )) && #??? warning message, option to set width, default to 220??? maybe a max width too

# Display the diff.
diff  --width="$(( display_width - 8 ))" --color=always --side-by-side                         \
    <(journalctl "${JCTL_ARGS[@]}" --no-pager -b -"$from_boot" | grep --only-matching ': .*$') \
    <(journalctl "${JCTL_ARGS[@]}" --no-pager -b -"$to_boot"   | grep --only-matching ': .*$') \
    | sed "/|[[:space:]]*:/s/.*/$(printf '\e[0;33m%s\e[0m' '&')/"                              \
    | less -S