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EXPR(1) General Commands Manual EXPR(1)

expr — evaluate expression

expr expression

The expr utility evaluates expression and writes the result on standard output.

All operators and operands must be passed as separate arguments. Several of the operators have special meaning to command interpreters and must therefore be quoted appropriately. All integer operands are interpreted in base 10.

Arithmetic operations are performed using signed integer math.

Operators are listed below in order of increasing precedence; all are left-associative. Operators with equal precedence are grouped within { } symbols.

expr1 | expr2
Return the evaluation of expr1 if it is neither an empty string nor zero; otherwise, returns the evaluation of expr2.
expr1 & expr2
Return the evaluation of expr1 if neither expression evaluates to an empty string or zero; otherwise, returns zero.
expr1 {=, >, >=, <, <=, !=} expr2
Return the results of integer comparison if both arguments are integers; otherwise, returns the results of string comparison using the locale-specific collation sequence. The result of each comparison is 1 if the specified relation is true, or 0 if the relation is false.
expr1 {+, -} expr2
Return the results of addition or subtraction of integer-valued arguments.
expr1 {*, /, %} expr2
Return the results of multiplication, integer division, or remainder of integer-valued arguments.
expr1 : expr2
The “:” operator matches expr1 against expr2, which must be a regular expression. The regular expression is anchored to the beginning of the string with an implicit “^”.

If the match succeeds and the pattern contains at least one regular expression subexpression “\(...\)”, the string corresponding to “\1” is returned; otherwise the matching operator returns the number of characters matched. If the match fails and the pattern contains a regular expression subexpression the null string is returned; otherwise 0.

Parentheses are used for grouping in the usual manner.

The expr utility exits with one of the following values:

0
the expression is neither an empty string nor 0.
1
the expression is an empty string or 0.
2
the expression is invalid.

  1. The following example adds one to the variable a.
    a=`expr $a + 1`
  2. The following example returns the filename portion of a pathname stored in variable a. The // characters act to eliminate ambiguity with the division operator.
    expr //$a : '.*/\(.*\)'
  3. The following example returns the number of characters in variable a.
    expr $a : '.*'

sh(1), test(1)

The expr utility conforms to IEEE Std 1003.2 (“POSIX.2”).

An expr utility first appeared in the Programmer's Workbench (PWB/UNIX). A public domain version of expr written by Pace Willisson <pace@blitz.com> appeared in 386BSD-0.1.

Initial implementation by Pace Willisson <pace@blitz.com> was largely rewritten by J.T. Conklin <jtc@FreeBSD.org>.

August 23, 2016 DragonFly-5.6.1