setexpr command¶

Synopsis¶

setexpr[.b, .w, .l .s] <name> [*]<value> <op> [*]<value2>
setexpr[.b, .w, .l] <name> [*]<value>
setexpr <name> fmt <format> [value]...
setexpr <name> gsub r s [t]
setexpr <name> sub r s [t]

Description¶

The setexpr command is used to set an environment variable to the result of an evaluation.

setexpr[.b, .w, .l .s] <name> [*]<value> <op> [*]<value2>: Set environment variable <name> to the result of the evaluated expression specified by <op>.
setexpr[.b, .w, .l] name [*]value: Load <value> into environment variable <name>
setexpr name fmt <format> value: Set environment variable <name> to the result of the C like format string <format> evaluation of <value>.
setexpr name gsub <r> <s> [<t>]: For each substring matching the regular expression <r> in the string <t>, substitute the string <s>. The result is assigned to <name>. If <t> is not supplied, use the old value of <name>.
setexpr name sub <r> <s> [<t>]: Just like gsub(), but replace only the first matching substring

The setexpr command takes the following arguments:

format

This parameter contains a C or Bash like format string. The number of arguments is limited to 4. The following format types are supported:

c: single character
d, i: decimal value
o: octal value
s: string
u: unsigned decimal value
x, X: hexadecimal value
‘%’: no conversion, instead a % character will be written

Backslash escapes:

" = double quote \ = backslash a = alert (bell) b = backspace c = produce no further output f = form feed n = new line r = carriage return t = horizontal tab v = vertical tab NNN = octal number (NNN is 0 to 3 digits)

name

The name of the environment variable to be set

op

‘|’: name = value | value2
‘&’: name = value & value2
‘+’: name = value + value2 (This is the only operator supported for strings. It acts as concatenation operator on strings)
‘^’: name = value ^ value2
‘-‘: name = value - value2
‘*’: name = value * value2
‘/’: name = value / value2
‘%’: name = value % value2

r

Regular expression

s

Substitution string

t

string

value

Can either be an integer value, a string. If the pointer prefix ‘*’ is given value is treated as memory address.

value2

See value

Example¶

=> setexpr foo fmt %d 0x100
=> echo $foo
256
=>

=> setexpr foo fmt 0x%08x 63
=> echo $foo
0x00000063
=>

=> setexpr foo fmt %%%o 8
=> echo $foo
%10
=>

Configuration¶

The setexpr gsub and sub operations are only available if CONFIG_REGEX=y.

Return value¶

The return value $? is set to 0 (true) if the operation was successful.

If an error occurs, the return value $? is set to 1 (false).