expr(1) - NetBSD Manual Pages

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EXPR(1)                     NetBSD Reference 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 are separate arguments to the expr utility.  Characters
     special to the command interpreter must be escaped.

     Operators are listed below in order of increasing precedence.  Operators
     with equal precedence are grouped within { } symbols.

     expr1 | expr2
             Returns the evaluation of expr1 if it is neither an empty string
             nor zero; otherwise, returns the evaluation of expr2.

     expr1 & expr2
             Returns the evaluation of expr1 if neither expression evaluates
             to an empty string or zero; otherwise, returns zero.

     expr1 {=, >, >=, <, <=, !=} expr2
             Returns the results of integer comparison if both arguments are
             integers; otherwise, returns the results of string comparison us-
             ing 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
             Returns the results of addition or subtraction of integer-valued
             arguments.

     expr1 {*, /, %} expr2
             Returns the results of multiplication, integer division, or re-
             mainder 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 regu-
             lar expression subexpression ``\(...\)'', the string correspond-
             ing to ``\1'' is returned; otherwise the matching operator re-
             turns 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.


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 : '.*'


RETURN VALUES

     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.
     >2      an error occurred (such as memory allocation failure).


STANDARDS

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

NetBSD 1.5.3                     July 3, 1993                                2