done

for name [in words]; do commands; donewhile condition; do commands; doneuntil condition; do commands; doneselect name [in words]; do commands; done

done is a shell reserved word, not a program: it terminates the body of a for, while, until, or select loop that was opened with do. Every do must be matched by a done, and the pair brackets the commands that run on each iteration.Because done ends a compound command, redirections and pipes written after it apply to the loop as a whole rather than to the last command inside it. `done > out.txt` sends every iteration's output to the file, opening it once, which is both faster and more correct than redirecting on each pass through the loop.The word is only special where a command is expected. Anywhere else, for instance as an argument, it is an ordinary string, which is why `echo done` simply prints the word.The exit status of a loop is the exit status of the last command run in its body, or 0 if the body never ran.

done is a reserved word, so it cannot be used as a function or command name without quoting. A do with no matching done leaves the shell waiting for more input, which shows up as a hung script or a continuation prompt rather than a clear syntax error.It is not universal across shells: fish and csh close their loops with end, so `done` belongs to the Bourne family (sh, bash, dash, ksh, zsh). It is also unrelated to `task done` in Taskwarrior, where `done` is an ordinary subcommand of that program rather than shell syntax.

The `do ... done` bracketing comes from the Bourne shell in Unix Version 7 (1979). Stephen Bourne took the style from ALGOL 68, where compound statements are closed by reversing the opening keyword, the same instinct that gives the shell `if ... fi` and `case ... esac`. Loops never acquired a reversed `od`, so they were given the plain word `done` instead. POSIX standardised the syntax, and it behaves identically in every Bourne-family shell today.

for(1), while(1), until(1), break(1), continue(1), bash(1)