Comments on: Multiple expression if statement in BASH http://crazedmonkey.com/blog/programming/multiple-expression-if-statement-in-bash.html Ian Stevens' weblog Mon, 08 Sep 2008 06:53:52 +0000 http://wordpress.org/?v=2.5 By: stef http://crazedmonkey.com/blog/programming/multiple-expression-if-statement-in-bash.html#comment-57211 stef Tue, 12 Aug 2008 12:21:54 +0000 http://crazedmonkey.com/blog/programming/multiple-expression-if-statement-in-bash.html#comment-57211 I concur, the logical AND always has precedence before the logical OR. Basic math logic that you learn in high school 4th year i think. See ya! I concur, the logical AND always has precedence before the logical OR. Basic math logic that you learn in high school 4th year i think.

See ya!

]]> By: Rechosen http://crazedmonkey.com/blog/programming/multiple-expression-if-statement-in-bash.html#comment-56677 Rechosen Wed, 06 Aug 2008 16:41:26 +0000 http://crazedmonkey.com/blog/programming/multiple-expression-if-statement-in-bash.html#comment-56677 According to tldp.org, the -a (for and) operator has precedence over -o (for or), which means that -a is evaluated and processed before -o. The following experiment shows it: foo=1 bar=2 if [ $foo -eq 2 -a $bar -eq 2 -o $bar -eq 1 ]; then echo "Or has precedence." else echo "And has precedence." fi The above returns "And has precedence." According to tldp.org, the -a (for and) operator has precedence over -o (for or), which means that -a is evaluated and processed before -o. The following experiment shows it:

foo=1
bar=2

if [ $foo -eq 2 -a $bar -eq 2 -o $bar -eq 1 ]; then
echo “Or has precedence.”
else
echo “And has precedence.”
fi

The above returns “And has precedence.”

]]> By: Tony http://crazedmonkey.com/blog/programming/multiple-expression-if-statement-in-bash.html#comment-56559 Tony Tue, 05 Aug 2008 17:23:35 +0000 http://crazedmonkey.com/blog/programming/multiple-expression-if-statement-in-bash.html#comment-56559 Great help Ian! Another evaluation that might be hepful... Let say you supposed to have two environment variables $A and $B(A and B could be files as well), you want to know if those values are set or not, you can use if [ -z $A -a -z $B ]; then echo "Please define A and B" fi this is useful when you have many conditions to evaluate Great help Ian!

Another evaluation that might be hepful…
Let say you supposed to have two environment variables $A and $B(A and B could be files as well), you want to know if those values are set or not, you can use
if [ -z $A -a -z $B ];
then
echo “Please define A and B”
fi

this is useful when you have many conditions to evaluate

]]> By: Ian Stevens http://crazedmonkey.com/blog/programming/multiple-expression-if-statement-in-bash.html#comment-38181 Ian Stevens Tue, 26 Feb 2008 03:54:54 +0000 http://crazedmonkey.com/blog/programming/multiple-expression-if-statement-in-bash.html#comment-38181 In this case, both $bar and $abc must be 1, regardless of the value of $foo. In this case, both $bar and $abc must be 1, regardless of the value of $foo.

]]> By: David http://crazedmonkey.com/blog/programming/multiple-expression-if-statement-in-bash.html#comment-38136 David Mon, 25 Feb 2008 19:13:25 +0000 http://crazedmonkey.com/blog/programming/multiple-expression-if-statement-in-bash.html#comment-38136 You can intermix the two, but how does it flow? IOW, if I say if [ $foo -eq 1 -o $bar -eq 1 -a $abc -eq 1 ] does that mean that either $foo or $bar can be 1 but $abc must be 1? Or does it mean that either $foo can be 1 or $bar and $abc can be 1? You can intermix the two, but how does it flow? IOW, if I say
if [ $foo -eq 1 -o $bar -eq 1 -a $abc -eq 1 ]
does that mean that either $foo or $bar can be 1 but $abc must be 1? Or does it mean that either $foo can be 1 or $bar and $abc can be 1?

]]> By: dave http://crazedmonkey.com/blog/programming/multiple-expression-if-statement-in-bash.html#comment-32636 dave Wed, 23 Jan 2008 01:38:20 +0000 http://crazedmonkey.com/blog/programming/multiple-expression-if-statement-in-bash.html#comment-32636 Thanks helped me solve my && || bools Thanks helped me solve my && || bools

]]> By: simon http://crazedmonkey.com/blog/programming/multiple-expression-if-statement-in-bash.html#comment-31495 simon Sat, 12 Jan 2008 17:52:31 +0000 http://crazedmonkey.com/blog/programming/multiple-expression-if-statement-in-bash.html#comment-31495 Quite useful since I googled "bash if" and your explanation was exactly what I needed! Quite useful since I googled “bash if” and your explanation was exactly what I needed!

]]> By: Durand http://crazedmonkey.com/blog/programming/multiple-expression-if-statement-in-bash.html#comment-27960 Durand Fri, 14 Dec 2007 21:18:02 +0000 http://crazedmonkey.com/blog/programming/multiple-expression-if-statement-in-bash.html#comment-27960 Thanks, that was very useful Thanks, that was very useful

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