One place where you learn not to use [ or [[, or be very careful about them is autoconf shell scripts (and that applies to more than `if`, like globs, sed, awk,

One place where you learn not to use [ or [[, or be very careful about them is autoconf shell scripts (and that applies to more than `if`, like globs, sed, awk, etc.). Because square brackets are quote characters in autoconf. https://www.gnu.org/savannah-checkouts/gnu/autoconf/manual/autoconf-2.71/html_node/Active-Characters.html https://www.gnu.org/savannah-checkouts/gnu/autoconf/manual/a...