Linux in a Nutshell, Fifth Edition

Arithmetic Expressions | 643

Bash and Korn

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In addition, some or all of the PS1–PS4 variables undergo different substitutions,

as outlined in the following table.

In Bash, the escape sequences are processed first, and then, if the promptvars

shell option is enabled via the shopt command (the default), the substitutions are

performed.

Arithmetic Expressions

The let command performs arithmetic. ksh88 and Bash are restricted to integer

arithmetic. ksh93 can do floating-point arithmetic as well. Both shells provide a

way to substitute arithmetic values (for use as command arguments or in vari-

ables); base conversion is also possible.

Operators

The shells use arithmetic operators from the C programming language; the

following table listing is in decreasing order of precedence. ksh88 does not

support the ++, --, unary +, ?:, comma or ** operators. Early versions of ksh93 do

not have **.

Substitution ksh88 ksh93 Bash

! for command number PS1 PS1

Escape sequences PS1, PS2, PS4

Variable substitution PS1 PS1 PS1, PS2, PS4

Command substitution PS1 PS1, PS2, PS4

Arithmetic substitution PS1 PS1, PS2, PS4

Expression Meaning

$(( expr )) Use the value of the enclosed arithmetic expression.

B#n Interpret integer n in numeric base B. For example, 8#100 specifies the octal equivalent of decimal 64.

Operator Description ...