show_line.sh

show_line() {

  default_context_lines=10

  usage() {
    echo "show_line <file> <line number> [number of context lines]"
    echo "OR:"
    echo "show_line <file>:<line number>[:<number of context lines>]"
    echo
    echo "Usage Examples:" 
    echo "  show_line /etc/profile 15"
    echo "  show_line /etc/profile 15 10"
    echo "  show_line /etc/profile:15"
    echo "  show_line /etc/profile:15:10"
  }

  check_digits() {
    if [[ "$1" = *[!0-9]* ]]
    then
	echo "Invalid $2: $1. It must be numeric"
	return 1
    else
	return 0
    fi
  }

  file="$1"

  if [[ "$file" = *:* ]]
  then
    line_number="${file#*:}"
    file="${file%%:*}"
    if [[ "$line_number" == *:* ]]
    then
      context_lines="${line_number#*:}"
      line_number="${line_number%%:*}"
    else
      context_lines="$default_context_lines"
    fi
  else
    line_number="$2"
    context_lines="${3:-$default_context_lines}"
  fi

  [[ "$file" == "" || "$line_number" == "" || "$context_lines" == "" ]] && usage && return 1

  [[ ! -r "$file" ]] && echo "Given file does not exist or is not readable: $file" && return 1

  check_digits "$line_number" "line number" || return 1
  check_digits "$context_lines" "context lines" || return 1

  cat -n "$file" | grep --color -"$context_lines" "^ *$line_number[^0-9]\+.*"

}