regular expression using a variable

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LEARN ABOUT OPENDARWIN

expr

EXPR(1) 						    BSD General Commands Manual 						   EXPR(1)

NAME

     expr -- evaluate expression

SYNOPSIS

     expr expression

DESCRIPTION

     The expr utility evaluates expression and writes the result on standard output.

     All operators are separate arguments to the expr utility.	Characters special to the command interpreter must be escaped.

     Operators are listed below in order of increasing precedence.  Operators with equal precedence are grouped within { } symbols.

     expr1 | expr2
	     Returns the evaluation of expr1 if it is neither an empty string nor zero; otherwise, returns the evaluation of expr2.

     expr1 & expr2
	     Returns the evaluation of expr1 if neither expression evaluates to an empty string or zero; otherwise, returns zero.

     expr1 {=, >, >=, <, <=, !=} expr2
	     Returns 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
	     Returns the results of addition or subtraction of integer-valued arguments.

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

     expr1 : expr2
	     The ``:'' operator matches expr1 against expr2, which must be a regular expression.  The regular expression is anchored to the begin-
	     ning of  the string with an implicit ``^''.  expr expects "basic" regular expressions, see re_format(7) for more information on regu-
	     lar expressions.

	     If the match succeeds and the pattern contains at least one regular expression subexpression ``(...)'', the string corresponding 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.

EXAMPLES

     1.   The following example adds one to the variable a.
		a=`expr $a + 1`

     2.   The following example returns the filename portion of a pathname stored in variable a.  The // characters act to eliminate ambiguity
	  with the division operator.
		expr //$a : '.*/(.*)'

     3.   The following example returns the number of characters in variable a.
		expr $a : '.*'

DIAGNOSTICS

     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.

STANDARDS

     The expr utility conforms to IEEE Std 1003.2 (``POSIX.2'').

BSD
								   July 3, 1993 							       BSD

Shell Programming and Scripting