Рейтинг@Mail.ru
[Войти] [Зарегистрироваться]

Наши друзья и партнеры

UnixForum
Беспроводные выключатели nooLite

Lines Club

Ищем достойных соперников.




Книги по Linux (с отзывами читателей)

Библиотека сайта или "Мой Linux Documentation Project"

Chapter 13. Arithmetic Expansion

Arithmetic expansion provides a powerful tool for performing (integer) arithmetic operations in scripts. Translating a string into a numerical expression is relatively straightforward using backticks, double parentheses, or let.

Variations

Arithmetic expansion with backticks (often used in conjunction with expr)
z=`expr $z + 3`          # The 'expr' command performs the expansion.
Arithmetic expansion with double parentheses, and using let

The use of backticks (backquotes) in arithmetic expansion has been superseded by double parentheses -- ((...)) and $((...)) -- and also by the very convenient let construction.

z=$(($z+3))
z=$((z+3))                                  #  Also correct.
                                            #  Within double parentheses,
                                            #+ parameter dereferencing
                                            #+ is optional.

# $((EXPRESSION)) is arithmetic expansion.  #  Not to be confused with
                                            #+ command substitution.



# You may also use operations within double parentheses without assignment.

  n=0
  echo "n = $n"                             # n = 0

  (( n += 1 ))                              # Increment.
# (( $n += 1 )) is incorrect!
  echo "n = $n"                             # n = 1


let z=z+3
let "z += 3"  #  Quotes permit the use of spaces in variable assignment.
              #  The 'let' operator actually performs arithmetic evaluation,
              #+ rather than expansion.

Examples of arithmetic expansion in scripts:

  1. Example 16-9

  2. Example 11-14

  3. Example 27-1

  4. Example 27-11

  5. Example A-16


Эта статья еще не оценивалась
Вы сможете оценить статью и оставить комментарий, если войдете или зарегистрируетесь.
Только зарегистрированные пользователи могут оценивать и комментировать статьи.

Комментарии отсутствуют