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-rw-r--r--toys/pending/expr.c26
1 files changed, 21 insertions, 5 deletions
diff --git a/toys/pending/expr.c b/toys/pending/expr.c
index 936f5fbd..c54a7255 100644
--- a/toys/pending/expr.c
+++ b/toys/pending/expr.c
@@ -13,15 +13,31 @@ config EXPR
bool "expr"
default n
help
- usage: expr args
+ usage: expr ARG1 OPERATOR ARG2...
- Evaluate expression and print result.
+ Evaluate expression and print result. For example, "expr 1 + 2".
- The supported operators, in order of increasing precedence, are:
+ The supported operators are (grouped from highest to lowest priority):
- | & = > >= < <= != + - * / % :
+ ( ) : * / % + - != <= < >= > = & |
- In addition, parentheses () are supported for grouping.
+ Each constant and operator must be a sparate command line argument.
+ All operators are infix, meaning they expect a constant (or expression
+ that resolves to a constant) on each side of the operator. Operators of
+ the same priority (within each group above) are evaluated left to right.
+ Parentheses may be used (as separate arguments) elevate the priority
+ of expressions.
+
+ Calling expr from a command shell requires a lot of \( or '*' escaping
+ to avoid interpreting shell control characters.
+
+ The & and | operators are logical, not bitwise) and may operate on
+ strings (a blank string is "false"). Comparison operators may also
+ operate on strings (alphabetical sort).
+
+ Constants may be strings or integers. Comparison, logical, and regex
+ operators may operate on strings (a blank string is "false"), other
+ operators require integers.
*/
// TODO: int overflow checking