expr

NAME

       expr - evaluate expressions

SYNOPSIS

       expr expression...
       expr {--help,--version}

DESCRIPTION

       This  manual page documents the GNU version of expr.  expr
       evaluates an expression and writes the result on its stan-
       dard output.  Each token of the expression must be a sepa-
       rate argument.  Operands are either  numbers  or  strings.
       Strings  are  not  quoted for expr, though you may need to
       quote them to protect them from the shell.   expr  coerces
       anything appearing in an operand position to an integer or
       a string depending on the operation being applied to it.

       The operators (in order of increasing precedence) are:

       |      Yields its first argument if it is neither null nor
              0,  otherwise  its  second  argument.   This is the
              usual `or' operation.

       &      Yields its first argument if  neither  argument  is
              null or 0, otherwise 0.

       <  <=  =  ==  !=  >=  >
              Compare  their  arguments and return 1 if the rela-
              tion is true, 0 otherwise.  (== is  a  synonym  for
              =.)  expr tries to coerce both arguments to numbers
              and do a numeric comparison; if it fails when  try-
              ing  to coerce either argument it then does a lexi-
              cographic comparison.

       +  -   Perform arithmetic operations.  Both arguments  are
              coerced  to numbers; an error occurs if this cannot
              be done.

       *  /  %
              Perform arithmetic operations (`%' is the remainder
              operation, as in C).  Both arguments are coerced to
              numbers; an error occurs if this cannot be done.

       :      Perform  pattern  matching.   Its   arguments   are
              coerced to strings and the second one is considered
              to be a regular expression, with a  `^'  implicitly
              added at the beginning.  The first argument is then
              matched against this regular  expression.   If  the
              match  succeeds  and part of the string is enclosed
              in `\(' and `\)', that part is the value of  the  :
              expression; otherwise an integer whose value is the
              number of characters matched is returned.   If  the
              match fails, the : operator returns the null string
              if `\(' and `\)' are used, otherwise 0.   Only  one
              `\(' and `\)' pair can be used.

       In addition, the following keywords are recognized:

       match string regex
              An alternative way to do pattern matching.  This is
              the same as ``string : regex''.

       substr string position length
              Return the substring of string beginning  at  posi-
              tion  with  length at most length.  If either posi-
              tion or length is negative or non-numeric, return a
              null string.

       index string character-class
              Return the first position in string where the first
              character in  character-class  was  found.   If  no
              character  in  character-class  is found in string,
              return 0.

       length string
              Return the length of string.

       Parentheses are used for grouping  in  the  usual  manner.
       The keywords cannot be used as strings.

   OPTIONS
       When  GNU  expr  is invoked with exactly one argument, the
       following options are recognized:

       --help Print a usage message on standard output  and  exit
              successfully.

       --version
              Print  version  information on standard output then
              exit successfully.

EXAMPLES

       To add 1 to the shell variable a:

              a=`expr $a + 1`

       The following may be used to print the non-directory  part
       of the file name stored in variable a (the value in a need
       not contain `/'):

              expr $a : '.*/\(.*\)' '|' $a

       Note the quoted shell metacharacters.

       expr returns the following exit status:

       0 if the expression is neither null nor 0,
       1 if the expression is null or 0,
       2 for invalid expressions.