cat-logs-once.sh

#/bin/bash

# comment

SAVE_DIR="$HOME/.cat-logs-once-store"
mkdir -p "${SAVE_DIR}"

target_file=$1
session_prefix=$2

if [ ! -f "${target_file}" ]; then
  echo "ERROR: File not found."
  exit
fi

file_last_line="last-line-${target_file//\//_}_${session_prefix}"

# read previous last line
marker_start_read=""
if [ -f "$file_last_line" ]; then
  marker_start_read=`cat "$file_last_line"`
fi

# check if file includes previous last line
includes_marker=""
if [ ! -z "$marker_start_read" ]; then
  includes_marker=`grep -F "${marker_start_read}" "${target_file}"`
fi

# save last line of file for next execution
marker_start_read_new=`tail -n1 "${target_file}"`
if [ ! -z "${marker_start_read_new}" ]; then
  echo "${marker_start_read_new}" > "$file_last_line"
fi

# just cat if no previous last line was found
if [ -z "$includes_marker" ]; then
  cat "$target_file"
  exit
fi

# echo lines after previous last line otherwise
approached_marker=false
while read line; do
  if [[ $approached_marker == false && "${line}" != "${marker_stop}" ]]; then
    continue
  else
    approached_marker=true
  fi

  echo $line
done < "${target_file}"