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Full Discussion: if/elif help
Homework and Emergencies Homework & Coursework Questions if/elif help Post 302536489 by ygemici on Tuesday 5th of July 2011 01:56:56 PM
Old 07-05-2011
Quote:
Originally Posted by Morgan Greywolf
You guys are conflating two different POSIX shell mechanisms here. One is the arithmetic expansion and the other is command expansion. These are different.

$(()) denotes arithmetic expansion, and $() denotes command expansion.

Shells that support $() or $(()) generally support both. For older shells that do not support these syntaxes, you need to use backticks (`) for command expansion and arithmetic expansion isn't supported. In arithmetic expansion, Corona rightly reports that you do not need $ to expand variables; however, you do need this in command expansion. For example:
Code:
$ x=1
$ y=2
$ echo $((x+y))
3

However:
Code:
$ echo $(x+y)
x+y: command not found

OTOH, if we give it an expr command:
Code:
$ echo $(expr x + y)
expr: non-numeric argument

We need explicit variable expansion:
Code:
$ echo $(expr $x + $y)

BTW, if we want compatibility with older shells that do not support arithmetic expansion, we generally are not going to be able to use new-style command expansion, so we want something like this, instead:

Code:
$ echo `expr $x + $y`
3

we dont conflating anything.we are talking just arithmetic expansion about all shell variants.
I was referring to mentioned syntax of "$((x+y))" expression gives error on the some older shells..
In addition, I mentioned what i identified a issue that is maybe a bug in ash.
because of it(false statement) does not give any error at try of 3rd.

regards
ygemici
 

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LEARN ABOUT REDHAT

expr

EXPR(1) 								FSF								   EXPR(1)

NAME

       expr - evaluate expressions

SYNOPSIS

       expr EXPRESSION
       expr OPTION

DESCRIPTION

       --help display this help and exit

       --version
	      output version information and exit

       Print the value of EXPRESSION to standard output.  A blank line below separates increasing precedence groups.  EXPRESSION may be:

       ARG1 | ARG2
	      ARG1 if it is neither null nor 0, otherwise ARG2

       ARG1 & ARG2
	      ARG1 if neither argument is null or 0, otherwise 0

       ARG1 < ARG2
	      ARG1 is less than ARG2

       ARG1 <= ARG2
	      ARG1 is less than or equal to ARG2

       ARG1 = ARG2
	      ARG1 is equal to ARG2

       ARG1 != ARG2
	      ARG1 is unequal to ARG2

       ARG1 >= ARG2
	      ARG1 is greater than or equal to ARG2

       ARG1 > ARG2
	      ARG1 is greater than ARG2

       ARG1 + ARG2
	      arithmetic sum of ARG1 and ARG2

       ARG1 - ARG2
	      arithmetic difference of ARG1 and ARG2

       ARG1 * ARG2
	      arithmetic product of ARG1 and ARG2

       ARG1 / ARG2
	      arithmetic quotient of ARG1 divided by ARG2

       ARG1 % ARG2
	      arithmetic remainder of ARG1 divided by ARG2

       STRING : REGEXP
	      anchored pattern match of REGEXP in STRING

       match STRING REGEXP
	      same as STRING : REGEXP

       substr STRING POS LENGTH
	      substring of STRING, POS counted from 1

       index STRING CHARS
	      index in STRING where any CHARS is found, or 0

       length STRING
	      length of STRING

       + TOKEN
	      interpret TOKEN as a string, even if it is a

	      keyword like `match' or an operator like `/'

       ( EXPRESSION )
	      value of EXPRESSION

       Beware that many operators need to be escaped or quoted for shells.  Comparisons are arithmetic if both ARGs are numbers, else lexicograph-
       ical.  Pattern matches return the string matched between ( and ) or null; if ( and ) are not used, they return the number of characters
       matched or 0.

AUTHOR

       Written by Mike Parker.

REPORTING BUGS

       Report bugs to <bug-coreutils@gnu.org>.

COPYRIGHT

       Copyright (C) 2002 Free Software Foundation, Inc.
       This is free software; see the source for copying conditions.  There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICU-
       LAR PURPOSE.

SEE ALSO

       The full documentation for expr is maintained as a Texinfo manual.  If the info and expr programs are properly installed at your site,  the
       command

	      info expr

       should give you access to the complete manual.

GNU coreutils 4.5.3						   February 2003							   EXPR(1)
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