Perl: open-ing a pipe for writing but program is not "waiting" for STDIN

Question

I am trying to run a program from a perl script. I redirect STDOUT and STDERR to two different files. The program I am running asks for a password that I try to print to the process handle but that doesn't work as the program immediately prints an authentication error warning me that I didn't write anything to STDIN.

The code I am using is similar to this:

my $s = qq(some_program > someprogram.out 2> someprogram.err);
open(my $f, "|$s") or die "Couldn't run program: $! $?";
# print `cat someprogram.out`; # An error has already been printed here!
print $f "password\n";
close $f or die "$!: $?";

I have run this in the perl debugger and noticed that when the debugger runs the open line, I can run the commented out print line and the error is already in the output file.

So, what am I forgetting to do in order for this to work? How do I tell open to "wait for STDIN"?

---UPDATE!

I did a test like this in the command line:

echo password | some_program

and the authentication error was printed. So it looks like some_program is really not reading from STDIN but from tty.

Is there a way to print to tty so the program can read the password from there in Perl?

Are you sure some_program is reading the password from standard input? If some_program is ssh, to give one of many examples, it is probably trying to read from the terminal, which is not necessarily the same thing as standard input. — mob
Hi, mob. I am not sure about that but it looks like this is the case. What options do I have? — Ivan Salazar
@mob @Len What I meant to say with "it looks like this is the case" is that some_program is not reading from STDIN and doing it from the terminal; not that it was ssh. I did a test like this in the command line: echo password | some_program and the authentication error appears. So the program is not reading from STDIN. — Ivan Salazar

AnBisw AnBisw · Accepted Answer · 2012-07-30T23:29:27

Considering some_program is a bash script (Shell) which accepts password on its command line, this can be done using system calls in perl. The system call, i.e. the program execution within Perl will not halt for the password, the best bet is to ask user for password before you call the program using a system call. Use backticks to perform system calls, something like below;

my $outfile="/path/to/someprogram.out";
my $errfile="/path/to/someprogram.err";
print "Enter password:\n";
$passwd=<>;
print "some_program $passwd\n";
`some_program $passwd > $outfile 2> $errfile`;

OR use system();

my $outfile="/path/to/someprogram.out";
my $errfile="/path/to/someprogram.err";
print "Enter password:\n";
$passwd=<>;
my $command="some_program $passwd > $outfile 2> $errfile";
print "$command\n";
system($command);

Perl: open-ing a pipe for writing but program is not "waiting" for STDIN

1 Answers