Match only some integers in a bash script conditional statement

A common techinque is:

IFS=. read maj min patch<< EOF
$IOS
EOF

if test $maj -ge 5 && test $min -ge 0; then
    echo ok
fi

This will parse $IOS into 3 components, $maj, $min, and $patch. If IOS is only two components, then $patch will be the empty string. Note that if either maj or min is not an integer (eg "5a"), a warning will be emitted and the test will fail. Also, I added the test for $min -ge 0 merely for demonstration, but that could be omitted (unless you may get negative version numbers!).

Something like

IOS=`/usr/bin/sw_vers -productVersion | awk -F '.' '{ORS=""; print $1; print "."; print $2;}'`

or

IOS=`/usr/bin/sw_vers -productVersion | cut -d . -f 1,2`