如何检查Perl脚本是否在终端中运行？

Question

I'm trying to determine, within a Perl script on Linux, whether it's running in a terminal.

That is, I need code that:

• returns true when simply running on the command-line
• also returns true when running ./myscript.pl | less ./myscript.pl | less or even ./myscript.pl </dev/null >/dev/null 2>/dev/null
• returns false when running in a cron job, or as a CGI script

Especially because of the second bullet, I can't use -t STDOUT and variations, and also IO::Interactive is of no use.

The information does appear to be available. If I run ps , it shows an entry like pts/2 in the TTY column, even when I run ./myscript.pl </dev/null >/dev/null 2>/dev/null , and ? when running as a cron job or CGI script.

Is there an elegant way to determine this in a Perl script? I'd rather not have to parse the output of ps .

Answer 1

You can try to open /dev/tty. This will work if you are in a terminal (even in a terminal on a remote computer). Otherwise, if the script is run via at or cron, it won't.

Note: this will only work on Unix systems.

Answer 2

Another answer to my own question. I studied the ps source to see how it determined the TTY, and it uses /proc/[pid]/stat .

use strict;
use warnings;
use 5.010;
use autodie;

sub isatty()
{
    # See http://www.kernel.org/doc/man-pages/online/pages/man5/proc.5.html
    open(my $stat, '<', "/proc/$$/stat");
    if (<$stat> =~ m{^\d+\s+\(.*\)\s+\w\s+\d+\s+\d+\s+\d+\s+(\d+)}) {
        return $1 > 0;
    }
    else {
        die "Unexpected format in /proc/$$/stat";
    }
}

Answer 3

PS应该帮助你。
ps aux | grep 'filename.pl'

Answer 4

At first you must check, output is associated with terminal by -t . Of course if you want, you can look at /proc/$pid/fd/1 , it is symlink to device. You can test it, if it is a terminal.

But if it is not enough, you can check enviromential variables by %ENV special hash table. CGI-BIN interface sets some of them. If you run script under cron, it sets some variable. If it is not enough, you can set it in /etc/crontab file and test in your script. It is for your needs what you'll do.

You should call that complete procedure only once. You cannot iterate it, because script environment won't change, until it is working.

You don't have to call any external commands, or you don't need special libarier. Only what you need, is windows incompatibilities. But if you are using windows10, then it has environment similar to linux based on ubuntu. then you cannot look out as strongly, as you do it making compatibility between win32api and unix like systems.

Answer 5

To partially answer my own question, the following does the trick:

sub isatty()
{
    my $tty = `/bin/ps -p $$ -o tty --no-headers`;
    $tty =~ s{[\s?]}{}g;
    return $tty;
}

Returns the TTY name if any (which is true), or "" if none (false).

I'd still prefer a solution without an external command...