These docs are under active development and cover the v0.20 Kobicha security model.
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expr

expr evaluates a single expression and prints its value.

expr expression

$ expr 6 + 7
13
$ expr length "Peios"
5

Each part of the expression — every number, operator, and keyword — is a separate argument. That is why the spaces matter: expr 6+7 is one argument and not an expression, while expr 6 + 7 is three.

Arithmetic

Operator Result
ARG1 + ARG2 Sum.
ARG1 - ARG2 Difference.
ARG1 * ARG2 Product.
ARG1 / ARG2 Integer quotient.
ARG1 % ARG2 Remainder.

Comparison

A comparison yields 1 for true and 0 for false. It is arithmetic when both sides are numbers, and lexical otherwise.

Operator True when…
ARG1 = ARG2 the two are equal.
ARG1 != ARG2 they are unequal.
ARG1 < ARG2 ARG1 is less.
ARG1 <= ARG2 ARG1 is less or equal.
ARG1 > ARG2 ARG1 is greater.
ARG1 >= ARG2 ARG1 is greater or equal.

Logic

Operator Result
ARG1 | ARG2 ARG1 if it is neither null nor 0; otherwise ARG2.
ARG1 & ARG2 ARG1 if neither argument is null or 0; otherwise 0.

String operations

Form Result
length STRING The number of characters in STRING.
substr STRING POS LENGTH LENGTH characters of STRING, counting POS from 1.
index STRING CHARS The position of the first of any of CHARS in STRING, or 0.
STRING : REGEXP Match REGEXP anchored at the start of STRING. Returns the matched length, or the text captured by \(…\).
match STRING REGEXP The same as STRING : REGEXP.

Many of these operators — *, <, |, ( — are also meaningful to a shell, so quote or escape them so they reach expr intact.

Exit status

expr's exit status reports on the value it computed:

Code Meaning
0 The result was neither null nor 0.
1 The result was null or 0.
2 The expression was syntactically invalid.
3 An error occurred during evaluation — such as division by zero.

See also