Shell Programming and Scripting

Hi wisecracker,
The command:

Code:

if ( [ "$a" = "A" ] || [ "$a" = "a" ] ) && ( [ "$b" = "B" ] || [ "$b" = "b" ] )

executes [ "$a" = "A" ] || [ "$a" = "a" ] in a subshell environment and if it evaluates to true it then evaluates [ "$b" = "B" ] || [ "$b" = "b" ] in a subshell execution environment. In this construct, the parentheses are shell operators.

The command:

Code:

if { [ "$a" = "A" ] || [ "$a" = "a" ]; } && { [ "$b" = "B" ] || [ "$b" = "b" ]; }

executes [ "$a" = "A" ] || [ "$a" = "a" ] in the current shell executionl environment and if it evaluates to true it then evaluates [ "$b" = "B" ] || [ "$b" = "b" ] in the current shelll execution environment. In this construct, the braces are shell keywords; not shell operators. The <semicolon>s are shell operators used to delimit the keywords. You could also see this written as:

Code:

if { [ "$a" = "A" ] || [ "$a" = "a" ]
   } && { [ "$b" = "B" ] || [ "$b" = "b" ]
   }

using <newline> instead of <semicolon> to delimit the brace keywords.

I used braces instead of parentheses to avoid creating two subshells.

Hi Don...

Thanks a lot...

The first part I had worked out by myself.

Your two derivatives I would never have known without your current post.

I checked my AudioScope.sh script as I have used '&&' inside it but not with any '||'s...

My mentor, you are... (YODA style. <wink>)