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fish

the `-t` operator for the `test` command does not correctly identify non-tty file descriptors

In bash/ksh/dash:

$ input_redirected() { [[ -t 0 ]] && echo input is not redirected || echo input is redirected; }
$ input_redirected foo
input is not redirected
$ input_redirected < /dev/null
input is redirected
$ cat /etc/passwd | input_redirected
input is redirected

in fish

$ function input_redirected; test -t 0; and echo not redirected; or echo redirected; end
$ input_redirected foo
not redirected
$ input_redirected < /dev/null
not redirected
$ cat /etc/passwd | input_redirected
not redirected

However, using isatty 0 instead of test -t 0 does provide the expected output.

What is test -t FD test doing in fish that it does not behave the same as POSIX-type shells?

Solution

  • It's a bug: https://github.com/fish-shell/fish-shell/issues/1228

    The workaround is to use command test, which is also what isatty does - see type isatty.