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       expr - evaluate arguments as an expression


       expr operand


       The expr utility shall evaluate an expression and write the result to standard output.




       The single expression evaluated by expr shall be formed from the operands, as described in
       the EXTENDED DESCRIPTION section. The application shall ensure that each of the expression
       operator symbols:

              (  )  |  &  =  >  >=  <  <=  !=  +  -  *  /  %  :

       and  the  symbols  integer  and  string in the table are provided as separate arguments to


       Not used.




       The following environment variables shall affect the execution of expr:

       LANG   Provide a default value for the internationalization variables that  are  unset  or
              null.  (See  the  Base  Definitions  volume  of  IEEE Std 1003.1-2001, Section 8.2,
              Internationalization Variables for the precedence of internationalization variables
              used to determine the values of locale categories.)

       LC_ALL If  set  to  a  non-empty  string  value,  override  the  values  of  all the other
              internationalization variables.


              Determine the locale for the behavior of ranges, equivalence  classes,  and  multi-
              character   collating  elements  within  regular  expressions  and  by  the  string
              comparison operators.

              Determine the locale for the interpretation of sequences of bytes of text  data  as
              characters  (for  example,  single-byte  as  opposed  to  multi-byte  characters in
              arguments) and the behavior of character classes within regular expressions.

              Determine the locale that should be used to  affect  the  format  and  contents  of
              diagnostic messages written to standard error.

              Determine the location of message catalogs for the processing of LC_MESSAGES .




       The  expr  utility  shall  evaluate  the  expression  and  write the result, followed by a
       <newline>, to standard output.


       The standard error shall be used only for diagnostic messages.




       The formation of the expression to be evaluated is  shown  in  the  following  table.  The
       symbols  expr,  expr1,  and  expr2  represent  expressions  formed from integer and string
       symbols and  the  expression  operator  symbols  (all  separate  arguments)  by  recursive
       application  of the constructs described in the table. The expressions are listed in order
       of increasing precedence,  with  equal-precedence  operators  grouped  between  horizontal
       lines. All of the operators shall be left-associative.

                       Expression       Description
                       expr1 | expr2    Returns the evaluation of expr1 if it is
                                        neither null nor zero; otherwise,
                                        returns the evaluation of expr2 if it is
                                        not null; otherwise, zero.
                       expr1 & expr2    Returns the evaluation of expr1 if
                                        neither expression evaluates to null or
                                        zero; otherwise, returns zero.
                                        Returns the result of a decimal integer
                                        comparison if both arguments are
                                        integers; otherwise, returns the result
                                        of a string comparison using the locale-
                                        specific collation sequence. The result
                                        of each comparison is 1 if the specified
                                        relationship is true, or 0 if the
                                        relationship is false.
                       expr1 = expr2    Equal.
                       expr1 > expr2    Greater than.
                       expr1 >= expr2   Greater than or equal.
                       expr1 < expr2    Less than.
                       expr1 <= expr2   Less than or equal.
                       expr1 != expr2   Not equal.
                       expr1 + expr2    Addition of decimal integer-valued
                       expr1 - expr2    Subtraction of decimal integer-valued
                       expr1 * expr2    Multiplication of decimal integer-valued
                       expr1 / expr2    Integer division of decimal integer-
                                        valued arguments, producing an integer
                       expr1 % expr2    Remainder of integer division of decimal
                                        integer-valued arguments.
                       expr1 : expr2    Matching expression; see below.
                       ( expr )         Grouping symbols. Any expression can be
                                        placed within parentheses. Parentheses
                                        can be nested to a depth of
                       integer          An argument consisting only of an
                                        (optional) unary minus followed by
                       string           A string argument; see below.

   Matching Expression
       The ':' matching operator shall compare the string resulting from the evaluation of  expr1
       with  the  regular  expression  pattern  resulting  from  the evaluation of expr2. Regular
       expression  syntax  shall  be  that  defined   in   the   Base   Definitions   volume   of
       IEEE Std 1003.1-2001, Section 9.3, Basic Regular Expressions, except that all patterns are
       anchored to the beginning of the string (that is, only sequences  starting  at  the  first
       character  of  a  string  are  matched  by  the  regular expression) and, therefore, it is
       unspecified whether '^' is a special character in  that  context.  Usually,  the  matching
       operator  shall  return  a  string  representing the number of characters matched ( '0' on
       failure).  Alternatively,  if  the  pattern  contains  at  least  one  regular  expression
       subexpression "[\(...\)]" , the string corresponding to "\1" shall be returned.

   String Operand
       A  string  argument  is an argument that cannot be identified as an integer argument or as
       one of the expression operator symbols shown in the OPERANDS section.

       The use of string arguments length, substr, index, or match produces unspecified results.


       The following exit values shall be returned:

        0     The expression evaluates to neither null nor zero.

        1     The expression evaluates to null or zero.

        2     Invalid expression.

       >2     An error occurred.



       The following sections are informative.


       After argument processing by the shell, expr is not  required  to  be  able  to  tell  the
       difference  between  an  operator and an operand except by the value. If "$a" is '=' , the

              expr $a = '='

       looks like:

              expr = = =

       as the arguments are passed to expr (and they all may be taken as the '='  operator).  The
       following works reliably:

              expr X$a = X=

       Also  note  that  this  volume  of  IEEE Std 1003.1-2001 permits implementations to extend
       utilities. The expr utility permits the integer arguments to  be  preceded  with  a  unary
       minus.  This  means  that  an  integer  argument could look like an option. Therefore, the
       conforming application must employ  the  "--"  construct  of  Guideline  10  of  the  Base
       Definitions  volume  of  IEEE Std 1003.1-2001,  Section 12.2, Utility Syntax Guidelines to
       protect its operands if there is any chance the first operand might be a negative  integer
       (or any string with a leading minus).


       The expr utility has a rather difficult syntax:

        * Many  of the operators are also shell control operators or reserved words, so they have
          to be escaped on the command line.

        * Each part of the expression is composed of separate  arguments,  so  liberal  usage  of
          <blank>s is required. For example:

                                 Invalid            Valid
                                 expr 1+2           expr 1 + 2
                                 expr "1 + 2"       expr 1 + 2
                                 expr 1 + (2 * 3)   expr 1 + \( 2 \* 3 \)

       In  many  cases,  the arithmetic and string features provided as part of the shell command
       language are easier to use than their equivalents in expr. Newly  written  scripts  should
       avoid expr in favor of the new features within the shell; see Parameters and Variables and
       Arithmetic Expansion .

       The following command:

              a=$(expr $a + 1)

       adds 1 to the variable a.

       The following command, for "$a" equal to either /usr/abc/file or just file:

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

       returns the last segment of a pathname (that is,  file).  Applications  should  avoid  the
       character '/' used alone as an argument; expr may interpret it as the division operator.

       The following command:

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

       is  a  better  representation of the previous example. The addition of the "//" characters
       eliminates any ambiguity about the division operator and simplifies the whole  expression.
       Also  note  that pathnames may contain characters contained in the IFS variable and should
       be quoted to avoid having "$a" expand into multiple arguments.

       The following command:

              expr "$VAR" : '.*'

       returns the number of characters in VAR.


       In an early proposal, EREs were used in the matching expression syntax.  This was  changed
       to BREs to avoid breaking historical applications.

       The  use  of  a  leading  circumflex  in  the  BRE  is unspecified because many historical
       implementations  have  treated  it  as  a  special   character,   despite   their   system
       documentation. For example:

              expr foo : ^foo     expr ^foo : ^foo

       return  3  and  0,  respectively,  on  those  systems; their documentation would imply the
       reverse. Thus, the anchoring condition is left unspecified to  avoid  breaking  historical
       scripts relying on this undocumented feature.




       Parameters and Variables , Arithmetic Expansion


       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2003 Edition, Standard for Information Technology  --  Portable  Operating  System
       Interface  (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by
       the Institute of Electrical and Electronics Engineers, Inc and  The  Open  Group.  In  the
       event  of  any  discrepancy  between this version and the original IEEE and The Open Group
       Standard, the original IEEE and The Open Group  Standard  is  the  referee  document.  The
       original Standard can be obtained online at .