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Diffstat (limited to 'Doc/Zsh/arith.yo')

-rw-r--r-- | Doc/Zsh/arith.yo | 53 |

1 files changed, 39 insertions, 14 deletions

diff --git a/Doc/Zsh/arith.yo b/Doc/Zsh/arith.yo index f08deb372..f22b35794 100644 --- a/Doc/Zsh/arith.yo +++ b/Doc/Zsh/arith.yo @@ -5,16 +5,42 @@ sect(Arithmetic Evaluation) )\ cindex(arithmetic evaluation) cindex(evaluation, arithmetic) -An ability to perform integer arithmetic is provided with the builtin tt(let). findex(let, use of) -Evaluations are performed using em(long) arithmetic. +The shell can perform integer arithmetic, either using the builtin tt(let), +or via a substitution of the form tt($((...))). Usually arithmetic is +performed with em(long) integers; however, on certain systems where a +em(long) has 4-byte precision, zsh may be compiled to use 8-byte precision +instead. This can be tested, for example, by giving the command +`tt(print - $(( 12345678901 )))'; if the number appears unchanged, the +precision is at least 8 bytes. + +The tt(let) builtin command takes arithmetic expressions as arguments; each +is evaluated separately. Since many of the arithmetic operators, as well +as spaces, require quoting, an alternative form is provided: for any +command which begins with a `tt(LPAR()LPAR())', all the characters until a +matching `tt(RPAR()RPAR())' are treated as a quoted expression and +arithmetic expansion performed as for an argument of tt(let). More +precisely, `tt(LPAR()LPAR())var(...)tt(RPAR()RPAR())' is equivalent to +`tt(let ")var(...)tt(")'. For example, the following statement + +example((( val = 2 + 1 ))) + +is equivalent to + +example(let "val = 2 + 1") + +both assigning the value 3 to the shell variable tt(foo) and returning a +zero status. + +cindex(bases, in arithmetic) +Numbers can be in bases other than 10. A leading `tt(0x)' or `tt(0X)' denotes hexadecimal. -Otherwise, numbers are of the form `[var(base)tt(#)]var(n)', +Numbers may also be of the form `var(base)tt(#)var(n)', where var(base) is a decimal number between two and thirty-six representing the arithmetic base and var(n) is a number in that base (for example, `tt(16#ff)' is 255 in hexadecimal). -If var(base) is omitted -then base 10 is used. For backwards compatibility the form +The var(base)tt(#) may also be omitted, in which case +base 10 is used. For backwards compatibility the form `tt([)var(base)tt(])var(n)' is also accepted. cindex(arithmetic operators) @@ -50,10 +76,17 @@ and XOR operators. An expression of the form `tt(#\)var(x)' where var(x) is any character gives the ascii value of this character and an expression of the form `tt(#)var(foo)' gives the ascii value of the first character of the value +of the parameter var(foo). Note that this is different from the expression +`tt($#)var(foo)', a standard parameter substitution which gives the length of the parameter var(foo). Named parameters and subscripted arrays can be referenced by name within an -arithmetic expression without using the parameter expansion syntax. +arithmetic expression without using the parameter expansion syntax. For +example, + +example((((val2 = val1 * 2)))) + +assigns twice the value of tt($val1) to the parameter named tt(val2). An internal integer representation of a named parameter can be specified with the tt(integer) builtin. @@ -63,11 +96,3 @@ findex(integer, use of) Arithmetic evaluation is performed on the value of each assignment to a named parameter declared integer in this manner. - -Since many of the arithmetic operators require -quoting, an alternative form of the tt(let) command is provided. -For any command which begins with a tt(LPAR()LPAR()), -all the characters until a matching tt(RPAR()RPAR()) -are treated as a quoted expression. -More precisely, `tt(LPAR()LPAR()) ... tt(RPAR()RPAR())' -is equivalent to `tt(let ")...tt(")'. |