https://fishshell.com/docs/current/cmds/string-sub.html
1> string sub --length 2 abcde2ab3
4> string sub -s 2 -l 2 abcde5bc6
7> string sub --start=-2 abcde8de9
10> string sub --end=3 abcde11abc12
13> string sub -e -1 abcde14abcd15
5 collapsed lines
16> string sub -s 2 -e -1 abcde17bcd18
19> string sub -s -3 -e -2 abcde20c