EXPR(1P)						     POSIX Programmer's Manual							  EXPR(1P)

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       This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
       ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME

       expr -- evaluate arguments as an expression

SYNOPSIS

       expr operand...

DESCRIPTION

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

OPTIONS

       None.

OPERANDS

       The single expression evaluated by expr shall be formed from the operand 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 expr.

STDIN

       Not used.

INPUT FILES

       None.

ENVIRONMENT VARIABLES

       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
		 POSIX.1-2008, 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.

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

       LC_CTYPE  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.

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

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

ASYNCHRONOUS EVENTS

       Default.

STDOUT

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

STDERR

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES

       None.

EXTENDED DESCRIPTION

       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  con-
       structs	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 nei- |
					       |	       | ther expression  evaluates  to  null  or |
					       |	       | zero; otherwise, returns zero. 	  |
					       +---------------+------------------------------------------+
					       |	       | Returns  the result of a decimal integer |
					       |	       | comparison if both arguments  are  inte- |
					       |	       | gers; otherwise, returns the result of a |
					       |	       | string comparison using the  locale-spe- |
					       |	       | cific	collation sequence. The result of |
					       |	       | each comparison is 1  if  the	specified |
					       |	       | relationship  is true, or 0 if the rela- |
					       |	       | tionship 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 argu- |
					       |	       | ments. 				  |
					       |expr1 - expr2  | Subtraction  of  decimal  integer-valued |
					       |	       | arguments.				  |
					       +---------------+------------------------------------------+
					       |expr1 * expr2  | Multiplication of decimal integer-valued |
					       |	       | arguments.				  |
					       |expr1 / expr2  | Integer division of decimal integer-val- |
					       |	       | ued  arguments,  producing  an   integer |
					       |	       | result.				  |
					       |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 |
					       |	       | {EXPR_NEST_MAX}.			  |
					       +---------------+------------------------------------------+
					       |integer        | An   argument	 consisting  only  of  an |
					       |	       | (optional) unary minus followed by  dig- |
					       |	       | its.					  |
					       |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 POSIX.1-2008, 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). Alterna-
       tively, if the pattern contains at least one regular expression subexpression "[(...)]", the string matched by the back-reference expres-
       sion "1" shall be returned. If the back-reference expression "1" does not match, then the null string 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.

EXIT STATUS

       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.

CONSEQUENCES OF ERRORS

       Default.

       The following sections are informative.

APPLICATION USAGE

       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 command:

	   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 POSIX.1-2008 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 POSIX.1-2008, Section 12.2, Utility Syntax Guidelines to pro-
       tect its operands if there is any chance the first operand might be a negative integer (or any string with a leading minus).

EXAMPLES

       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> characters 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 Section 2.5, Parameters and Variables
       and Section 2.6.4, 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 opera-
       tor 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.

RATIONALE

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

       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 unspeci-
       fied to avoid breaking historical scripts relying on this undocumented feature.

FUTURE DIRECTIONS

       None.

SEE ALSO

       Section 2.5, Parameters and Variables, Section 2.6.4, Arithmetic Expansion

       The Base Definitions volume of POSIX.1-2008, Chapter 8, Environment Variables, Section 9.3, Basic Regular Expressions, Section 12.2,  Util-
       ity Syntax Guidelines

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C)  2013  by	the  Institute	of
       Electrical and Electronics Engineers, Inc and The Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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 Stan-
       dard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE
/The Open Group						       2013								  EXPR(1P)