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EXPR(1)                DragonFly General Commands Manual               EXPR(1)

NAME
     expr -- evaluate expression

SYNOPSIS
     expr expression

DESCRIPTION
     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.

EXIT STATUS
     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.

EXAMPLES
     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 : '.*'

SEE ALSO
     sh(1), test(1)

STANDARDS
     The expr utility conforms to IEEE Std 1003.2 (``POSIX.2'').

HISTORY
     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.

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

DragonFly 4.5                   August 23, 2016                  DragonFly 4.5