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Full Discussion: how to use expr
Operating Systems Linux Red Hat how to use expr Post 302273714 by jim mcnamara on Monday 5th of January 2009 02:52:13 PM
Old 01-05-2009
escape the * it is a shell metacharacter
Code:
a=$( expr 13 \* 3)
# or
a=`expr 13 \* 3`

This User Gave Thanks to jim mcnamara For This Post:
 

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test(1) 						      General Commands Manual							   test(1)

Name
       test - test conditional expression

Syntax
       test expr
       [ expr ]

Description
       The  command  evaluates the expression expr.  If the value of expr is true, the command returns a zero exit status; otherwise, it returns a
       nonzero exit status.  The command also returns a nonzero exit status if no arguments are specified.

Options
       The following primitives are used to construct expr:

       -r file		   Tests if the file exists and is readable.

       -w file		   Tests if the file exists and is writable.

       -f file		   Tests if the file exists and is not a directory.

       -d file		   Tests if the file exists and is a directory.

       -s file		   Tests if the file exists and has a size greater than zero.

       -t [ fildes ]	   Tests if the open file, whose file descriptor number is fildes (1 by default), is associated with a terminal device.

       -z s1		   Tests if the length of string s1 is zero.

       -n s1		   Tests if the length of the string s1 is nonzero.

       s1 = s2		   Tests if the strings s1 and s2 are equal.

       s1 != s2 	   Tests if the strings s1 and s2 are not equal.

       s1		   Tests if s1 is not the null string.

       n1 -eq n2	   Tests if number1 equals number2.

       n1 -ge n2	   Tests if number1 is greater than or equal to number2.

       n1 -gt n2	   Tests if number1 is greater than number2.

       n1 -le n2	   Tests if number1 is less than or equal to number2.

       n1 -lt n2	   Tests if number1 is less than number2.

       n1 -ne n2	   Tests if number1 is not equal to number2.

       These primitives can be combined with the following operators:

       !expr		   Negates evaluation of expression.

       expr -a expr	   Tests logical and of two expressions.

       expr -o expr	   Tests logical or of two expressions.

       ( expr... )	   Groups expressions.

       The -a operator takes precedence over the -o operator.  Note that all the operators and flags are separate  arguments  to  Note	also  that
       parentheses are meaningful to the Shell and must be escaped.

See Also
       find(1), sh(1), test(1sh5)

																	   test(1)
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