10.7 Parentheses in Shell Scripts

Beware of two opening parentheses in a row, as some shell implementations mishandle them. For example, ‘pdksh’ 5.2.14 misparses the following code:

     if ((true) || false); then
       echo ok
     fi

To work around this problem, insert a space between the two opening parentheses. There is a similar problem and workaround with ‘$((’; see Shell Substitutions.

Posix requires support for case patterns with opening parentheses like this:

     case $file_name in
     (*.c) echo "C source code";;
     esac

but the ( in this example is not portable to many older Bourne shell implementations. It can be omitted safely.