What keyword is missing from this code sample of a shell script? ____ i in *.txt; do echo $i done

The structure `for variable in list; do commands; done` is the standard syntax for a `for` loop in bash and other shells. In this example, `for i in *.txt` means the loop will iterate over each file ending with `.txt` in the current directory, assigning each filename to the variable `i`.

`loop` is not a valid keyword for initiating a loop in bash scripting; it's a generic term.

`until` is used for `until` loops, which execute commands repeatedly as long as a command's exit status is non-zero (false), following the syntax `until condition; do commands; done`.

`while` is used for `while` loops, which execute commands repeatedly as long as a command's exit status is zero (true), following the syntax `while condition; do commands; done`.