Differences between declare, typeset and local variable in Bash

• Difference between typeset and declare:

The former is more portable(e.g. ksh), while the latter is more preferable when portability is not a concern.

• Difference between declare(or typeset) and local when used inside a function:

The former implies the latter, but more powerful. For example, declare -i x makes x have the integer attribute, declare -r x makes x readonly, etc.