`EXPR`

Evaluate infix expression

Evaluate an integer expression and return its value as the command’s result. Nothing is printed unless the expression is invalid (Invalid expression: <text>). The value is available afterwards as $?, but only until the next command line: when each command is sent with its own bcmcmd call, $? already reads 0 in the next call. Read it on the same line (expr …; echo $?), or test the value with if (see below).

All arguments are joined without spaces, so expr 1 + 2 and expr 1+2 are the same. The text is limited to 127 characters; anything longer is silently cut off. Arithmetic is unsigned 32-bit. Operators, from highest to lowest precedence: ( ); unary - + ~ !; * / %; + -; << >>; < <= > >=; == !=; &; ^; |; &&; || (the same order as in C). Division or modulo by zero is an invalid expression. Numbers use the shell’s formats (0x, leading 0, 0b).

Because the value is the command’s result:

only a value of 0 counts as success, which inverts the result in if (write if !"expr …" to test for non-zero);
values that look like error codes (0xFFFFFFFF, 0xFFFFFFFE, …) are taken as errors: the shell may print expr’s usage or a Failed to execute line;
a line starting with expr never counts as a failure inside an rcload script.

Read-only.

Hardware-validated

drivshell> expr (1 << 4) + 2
drivshell> echo $?
0

Sent as two bcmcmd calls, as above, the echo prints 0, not 18. On one line it should print the value:

Hardware-validated

drivshell> expr (1 << 4) + 2; echo $?
18

Built-in help

Parameters: <c-style arithmetic expression>
    Evaluates an expression and sets the result as the return value.

EXPR

`EXPR`