expr(1)								       expr(1)

NAME    [Toc]    [Back]

     expr - evaluate arguments as an expression

SYNOPSIS    [Toc]    [Back]

     expr arguments

DESCRIPTION    [Toc]    [Back]

     The arguments are taken as	an expression.	After evaluation, the result
     is	written	on the standard	output.	 Terms of the expression must be
     separated by blanks.  Characters special to the shell must	be escaped.
     Note that 0 is returned to	indicate a zero	value, rather than the null
     string.  Strings containing blanks	or other special characters should be
     quoted.  Integer-valued arguments may be preceded by a unary minus	sign.
     Internally, integers are treated as 32-bit, 2s complement numbers.	 The
     length of the expression is limited to 512	bytes.	expr processes
     supplementary code	set characters according to the	locale specified in
     the LC_CTYPE environment variable [see LANG on environ(5)].  In regular
     expressions, pattern searches are performed on characters,	not bytes, as
     described in regcomp(5).

     The operators and keywords	are listed below.  Characters that need	to be
     escaped in	the shell [see sh(1)] are preceded by \.  The list is in order
     of	increasing precedence, with equal precedence operators grouped within
     {}	symbols.

     expr1 <b>\| expr2
	  returns the evaluation of expr1 if it	is neither null	nor 0,
	  otherwise returns the	evaluation of expr2.

     expr1 <b>\& expr2
	  returns the evaluation of expr1 if neither expression	evaluates to
	  null or 0, otherwise returns 0.

	  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 will be 1 if the specified	relationship is	true, or 0 if
	  the relationship is false.

     expr1 { =,	\>, \>=, \<, \<=, != } expr2
	  returns the result of	an integer comparison if both arguments	are
	  integers, otherwise returns the result of a lexical comparison.

     expr1 { +,	- } expr2
	  addition or subtraction of decimal integer-valued arguments.

     expr1 { \*, /, % }	expr2
	  multiplication, division, or remainder of the	decimal	integer-valued
	  arguments.






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expr(1)								       expr(1)



     expr1 <b>: expr2
	  The matching operator	: compares expr1 with expr2, which must	be a
	  regular expression.  Regular expression syntax is defined is defined
	  in the regcomp(5) man	page under the section titled: Basic Regular
	  Expression, Normally,	the matching operator returns the number of
	  bytes	matched	(0 on failure).	 Alternatively,	if the pattern
	  contains at least one	regular	expression subexpression [\( . . .\)],
	  the string corresponding to \1 will be returned.

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

EXAMPLES    [Toc]    [Back]

     Add 1 to the shell	variable a:

	  a=`expr $a + 1`

     The following example emulates basename(1)-it returns the last segment of
     the path name $a.	For $a equal to	either /usr/abc/file or	just file, the
     example returns file.  (Watch out for / alone as an argument:  expr takes
     it	as the division	operator; see the NOTES	below.)

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

     Here is a better version of the previous example.	The addition of	the //
     characters	eliminates any ambiguity about the division operator and
     simplifies	the whole expression.

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

     Return the	number of characters in	$VAR:

	  expr $VAR : '.*'

FILES    [Toc]    [Back]

     /usr/lib/locale/locale<b>/LC_MESSAGES/uxcore.abi
	  language-specific message file [See LANG on environ (5).]

SEE ALSO    [Toc]    [Back]

     regcomp(5), sh(1)

STDOUT    [Toc]    [Back]

     expr will evaluate	the expression and write the result to standard
     output. The character 0 will be written to	indicate a zero	value and
     nothing will be written to	indicate a null	string.

STDERR    [Toc]    [Back]

     Used only for diagnostic messages.







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expr(1)								       expr(1)



DIAGNOSTICS
     As	a side effect of expression evaluation,	expr returns the following
     exit values:
      0	  if the expression is neither null nor	0
      1	  if the expression is null or 0
      2	  for invalid expressions.
     >2	  An error occurred.

     syntax error     for operator/operand errors
     non-numeric argument
		      if arithmetic is attempted on such a string

NOTES    [Toc]    [Back]

     After argument processing by the shell, expr cannot tell the difference
     between an	operator and an	operand	except by the value.  If $a is an =,
     the command:

	  expr $a = '='

     looks like:

	  expr = = =

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

	  expr X$a = X=


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