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✏️ Editing: journalctl

#!/bin/bash -e
# Copyright 1999-2024. WebPros International GmbH. All rights reserved.

usage()
{
  cat <<-EOT
	Usage: journalctl [fetch|first] [OPTIONS] [journalctl-OPTIONS]
        Print journalctl logs with commands:
		fetch            Print *all* lines matching the criteria
		first            Print first line matching the criteria
	Print journalctl logs with OPTIONS:
		--grep PATTERN   Search with PATTERN
		--lines COUNT    Limit match count

As this is designed as a wrapper on journalctl utility, other
	journalctl-OPTIONS are transparently supported.

-h, --help       Display this help and exit
	EOT
  exit 2
}

is_journalctl_grep_flag_supported() {
  if { ! journalctl --grep= --lines=0 --no-pager --quiet 2>&1 >&3 3>&- | grep -q '^' >&2; } 3>&1; then
    echo -n 1
  fi
}

main() {
  local command="$1"
  [ -n "$command" ] || usage
  shift

local grep_pattern lines_count
  local args=()
  while [[ $# -gt 0 ]]; do
    case "$1" in
    --grep)
      grep_pattern="$2"
      shift 2 || usage
      ;;
    --grep=*)
      grep_pattern=${1#--grep=}
      shift
      ;;
    --lines)
      lines_count="$2"
      shift 2 || usage
      ;;
    --lines=*)
      lines_count=${1#--lines=}
      shift
      ;;
    -h|--help)
      usage
      ;;
    *)
      args+=("$1")
      shift
      ;;
    esac
  done

[ -z "$grep_pattern" ] || local grep_flag_supported=$(is_journalctl_grep_flag_supported)
  [ "$PL_JOURNALCTL_GREP_UNSUPPORTED" != "1" ] || local grep_flag_supported=

[ "$command" != "first" ] || lines_count=

local journalctl_args=("--no-pager" "--quiet")
  local grep_args

[ -z "$grep_pattern" ] || grep_pattern=$(echo -n "$grep_pattern" | sed 's;$\[\|\]$;\\\1;g')
  if [ -n "$grep_flag_supported" ]; then
    [ -z "$grep_pattern" ] || journalctl_args+=("--grep=$grep_pattern")
    [ -z "$lines_count"  ] || journalctl_args+=("--lines=$lines_count")
  else
    if [ -n "$grep_pattern" ]; then
      if [ -n "$lines_count" ]; then
        case "$lines_count" in
          \+*)
            lines_count=${lines_count##+}
            ;;
          \-*)
            lines_count=${lines_count##-}
            ;;
        esac
      fi
      # PROBLEM: We receive json text from journalctl which makes no sense to grep it literally but only the MESSAGE part
      # Also log message could have escaped quote characters within. Below is thought to be the fastest solution.

# If the message include '"', it should already be '\"'; so grep_pattern should look for '\\"' to get literal '\'
      grep_pattern=$(echo -n "$grep_pattern" | sed 's;";\\\\";g')
      grep_pattern=$(echo -n "$grep_pattern" | sed 's;-;\\-;g')
      # We match first item by '"MESSAGE"'
      local pre='\s*"MESSAGE"\s*:\s*"'
      # We match termination by ', "' OR ' }' at the end, it should match due to JSON format
      local post='"(\s*,\s*"|\s*})'
      grep_args=("-Ei" "${pre}.*${grep_pattern}.*${post}")
      [ -z "$lines_count" ] || grep_args+=("-m" "$lines_count")
    else
      [ -z "$lines_count" ] || journalctl_args+=("--lines=$lines_count")
    fi
  fi

[ "$command" != "first" ] || journalctl_args+=("--lines=+1")

export SYSTEMD_COLORS=false
  case "$command" in
    fetch|first)
      if [ -n "$grep_flag_supported" ]; then
        journalctl "${args[@]}" "${journalctl_args[@]}"
      else
        if [ -z "$grep_args" ]; then
          journalctl "${args[@]}" "${journalctl_args[@]}"
        else
          journalctl "${args[@]}" "${journalctl_args[@]}" | grep "${grep_args[@]}"
        fi
      fi
    ;;
    *)
      echo "Unknown command: ${command}" >&2
      usage
    ;;
  esac
}

main "$@"

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