/usr/share/fish/functions/isatty.fish is in fish-common 2.4.0-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 | function isatty -d "Tests if a file descriptor is a tty"
set -l fd 0
if count $argv >/dev/null
switch $argv[1]
case -h --h --he --hel --help
__fish_print_help isatty
return 0
case stdin ''
set fd 0
case stdout
set fd 1
case stderr
set fd 2
case '*'
set fd $argv[1]
end
end
# Use `command test` because `builtin test` doesn't open the regular fd's.
# See https://github.com/fish-shell/fish-shell/issues/1228
command test -t "$fd"
end
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