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nested logical expression in bash shell

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# 1  
Old 01-21-2012
nested logical expression in bash shell
Please tell me how to nest logical expressions in bash. I would like to nest logical expressions for arguments of the "test" command on bash.

The following pseudo-code shows my intention.

Code:
// pseudo code

if (exp1 AND (exp2 OR exp3))
{
  Output true;
}
else
{
  Output false;
}


The following bash code failed.

Code:
if test 1 -eq 1 -a ( 2 -eq 2 -o 2 -eq 3 )
then
  echo "true"
else
  echo "false"
fi

The above bash code ended up with the following error message.

syntax error near unexpected token `('


Many thanks, in advance.
# 2  
Old 01-21-2012
Code:
if [[ 1 -eq 1 && ( 2 -eq 2 || 2 -eq 3 ) ]]
then
  echo "true"
else
  echo "false"
fi

--ahamed
# 3  
Old 01-21-2012
-a and -o are deprecated... For POSIX compliancy use:

Code:
if test 1 -eq 1 && ( test 2 -eq 2 || test 3 -eq 3 )
then
  echo "true"
else
  echo "false"
fi

or the synonym:
Code:
if [ 1 -eq 1 ] && ( [ 2 -eq 2 ] || [ 3 -eq 3 ] );

This User Gave Thanks to Scrutinizer For This Post:
LessNux
# 4  
Old 01-21-2012
hi,

Quote:
Originally Posted by Scrutinizer
-a and -o are deprecated
Shell & Utilities - Single UNIX Specifications warns to not use them if script's input may be such strings.
I didn't find where it tells they're deprecated.

edit: or is it what means "deprecated"
Last edited by daPeach; 01-21-2012 at 07:25 PM..
# 5  
Old 01-22-2012
They advise not to use them, but the specification also says they have been marked obsolescent and that script should be converted:
Quote:
The XSI extensions specifying the -a and -o binary primaries and the '(' and ')' operators have been marked obsolescent. (Many expressions using them are ambiguously defined by the grammar depending on the specific expressions being evaluated.) Scripts using these expressions should be converted to the forms given below. Even though many implementations will continue to support these obsolescent forms, scripts should be extremely careful when dealing with user-supplied input that could be confused with these and other primaries and operators. Unless the application developer knows all the cases that produce input to the script, invocations like:

test "$1" -a "$2"

should be written as:

test "$1" && test "$2"
test
This User Gave Thanks to Scrutinizer For This Post:
daPeach
# 6  
Old 02-28-2012
Using the recommended operators how can i write the following?
Code:
if NOT [ $var -eq 'a' || $var = 'b' || $var = 'c' ]
then
 ....
fi

I want to keep the '||' clause and do not want to translate into
Code:
if [ $var -ne 'a' && $var -ne 'b' && $var -ne 'c' ]

because using 'NOT' equivalent ahead upfront is much easier to understand the logic

I am using Korn shell

Thanks,
-srinivas y.
Last edited by ysrini; 02-28-2012 at 12:45 AM..
# 7  
Old 02-28-2012
I think either of these are acceptable in Ksh or bash depending on your preference/need for single or double bracketed expressions:

Code:
if   ! [ $1 == "foo" ] || [ $1 == "bar" ]
then
    echo true
else
    echo false
fi

if  ! [[ $1 == "foo"  ||  $1 == "bar" ]]
then
    echo true
else
    echo false
fi

This User Gave Thanks to agama For This Post:
ysrini
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