How do I lowercase/uppercase strings with a shortcut in the terminal?

Solution 1:

Bash (readline, actually) does have support for this. Check the list of readline commands for text:

upcase-word (M-u)
Uppercase the current (or following) word. With a negative argument, uppercase the previous word, but do not move the cursor.

downcase-word (M-l)
Lowercase the current (or following) word. With a negative argument, lowercase the previous word, but do not move the cursor.

capitalize-word (M-c)
Capitalize the current (or following) word. With a negative argument, capitalize the previous word, but do not move the cursor.

M here is the Meta key, which is usually Alt.

Solution 2:

Use alt + u to make words uppercase.

Use alt + l to make words lowercase.