# Use colours for grep if possible.
if grep -V 2>/dev/null | grep GNU >/dev/null; then
  alias grep='grep --color=auto'

  # Old versions of grep understand GREP_COLOR.
  export GREP_COLOR='0;33'

  # Newer versions allow setting colours based on context, using GREP_COLORS.
  # cx: Lines of context; sl: Matching lines; mt: Search string; fn: Filename
  # ln: Line number; bn: Byte offset; se: Separators.
  colours=$(tput colors 2>/dev/null)
  [ -z "$colours" ] && colours=0
  if [ $colours = 256 ]; then
    export GREP_COLORS='cx=38;5;246:sl=:mt=33:fn=38;5;25:ln=38;5;82:bn=33:se=38;5;246'
  elif [ $colours -gt 88 ]; then
    export GREP_COLORS='cx=38;5;84:sl=:mt=33:fn=38;5;22:ln=38;5;44:bn=33:se=38;5;84'
  else
    export GREP_COLORS='cx=31:sl=:mt=33:fn=36:ln=34:bn=33:se=31'
  fi
fi