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EXPR(1)                 FreeBSD General Commands Manual                EXPR(1)

     expr -- evaluate expression

     expr [-e] expression

     The expr utility evaluates expression and writes the result on standard

     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.  If the -e
     flag is specified, arithmetic uses the C intmax_t data type (the largest
     integral type available), and expr will detect arithmetic overflow and
     return an error indication.  If a numeric operand is specified which is
     so large as to overflow conversion to an integer, it is parsed as a
     string instead.  If -e is not specified, arithmetic operations and pars-
     ing of integer arguments will overflow silently according to the rules of
     the C standard, using the long data type.

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

     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

     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
             basic 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
             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 makes no lexical distinction between arguments which may
     be operators and arguments which may be operands.  An operand which is
     lexically identical to an operator will be considered a syntax error.
     See the examples below for a work-around.

     The syntax of the expr command in general is historic and inconvenient.
     New applications are advised to use shell arithmetic rather than expr.

   Compatibility with previous implementations
     Unless FreeBSD 4.x compatibility is enabled, this version of expr adheres
     to the POSIX Utility Syntax Guidelines, which require that a leading
     argument beginning with a minus sign be considered an option to the pro-
     gram.  The standard -- syntax may be used to prevent this interpretation.
     However, many historic implementations of expr, including the one in pre-
     vious versions of FreeBSD, will not permit this syntax.  See the examples
     below for portable ways to guarantee the correct interpretation.  The
     check_utility_compat(3) function (with a utility argument of ``expr'') is
     used to determine whether compatibility mode should be enabled.  This
     feature is intended for use as a transition and debugging aid, when expr
     is used in complex scripts which cannot easily be recast to avoid the
     non-portable usage.  Enabling compatibility mode also implicitly enables
     the -e option, since this matches the historic behavior of expr in
     FreeBSD.  For historical reasons, defining the environment variable
     EXPR_COMPAT also enables compatibility mode.

     EXPR_COMPAT  If set, enables compatibility mode.

     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.

     +o   The following example (in sh(1) syntax) adds one to the variable a:
               a=$(expr $a + 1)

     +o   This will fail if the value of a is a negative number.  To protect
         negative values of a from being interpreted as options to the expr
         command, one might rearrange the expression:
               a=$(expr 1 + $a)

     +o   More generally, parenthesize possibly-negative values:
               a=$(expr \( $a \) + 1)

     +o   This example prints the filename portion of a pathname stored in
         variable a.  Since a might represent the path /, it is necessary to
         prevent it from being interpreted as the division operator.  The //
         characters resolve this ambiguity.
               expr "//$a" : '.*/\(.*\)'

     The following examples output the number of characters in variable a.
     Again, if a might begin with a hyphen, it is necessary to prevent it from
     being interpreted as an option to expr.

     +o   If the expr command conforms to IEEE Std 1003.1-2001 (``POSIX.1''),
         this is simple:
               expr -- "$a" : ".*"

     +o   For portability to older systems, however, a more complicated command
         is required:
               expr \( "X$a" : ".*" \) - 1

     sh(1), test(1), check_utility_compat(3)

     The expr utility conforms to IEEE Std 1003.1-2001 (``POSIX.1''), provided
     that compatibility mode is not enabled.  The -e flag is an extension.

FreeBSD 6.2                      July 12, 2004                     FreeBSD 6.2


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