mjhjmtu

Perl, Ruby and PHP can detect stdin:

$ perl -e 'print -t ? "no stdin" : "stdin"'
no stdin

$ echo | perl -e 'print -t ? "no stdin" : "stdin"'
stdin

$ ruby -e 'puts $stdin.isatty ? "no stdin" : "stdin"'
no stdin

$ echo | ruby -e 'puts $stdin.isatty ? "no stdin" : "stdin"'
stdin

$ php -r 'print posix_isatty(STDIN) ? "no stdin" : "stdin";'
no stdin

$ echo | php -r 'print posix_isatty(STDIN) ? "no stdin" : "stdin";'
stdin

Does Awk have some way to do this? I tried ARGC but its the same in both cases:

$ awk 'BEGIN print ARGC == 1 ? "no stdin" : "stdin"'
no stdin

$ echo | awk 'BEGIN print ARGC == 1 ? "no stdin" : "stdin"'
no stdin

Your perl, ruby and php examples test whether stdin exists. Your awk approach just tests whether stdin should be used.

You can use system("tty") in awk to do that.

ARGC is the number of command-line arguments present. (indexed from 1)

In both mentioned cases the awk command/expression 'BEGIN print ARGC == 1 ? "no stdin" : "stdin"' is considered as the 1st argument independently of whether any data was piped to the current command.

To check for the file name of the terminal connected to standard input:

echo "a" | awk 'BEGIN "tty" '
stdin

awk 'BEGIN "tty" '
no stdin