I can replicate on Linux. With an empty con dir in current dir, debugger does not break until program exits. If ./con is a file, it writes to it and enters some kind of never-ending loop, as you say.

strace perl -d a.pl shows this:

newfstatat(AT_FDCWD, "con", ..., ...)

Then, if con is found, it is opened with openat(AT_FDCWD, "con", O_RDWR|O_CREAT|O_TRUNC|O_CLOEXEC, 0666) and it is writing to it.

perl a.pl does not look for con

The flag AT_FDCWD has the meaning of "relative to current dir", i.e. where you execute from and not where script is located.

documentation mentions it:

If there is a TTY, we have to determine who it belongs to before we ca
+n proceed. If this is a slave editor or graphical debugger (denoted b
+y the first command-line switch being '-emacs'), we shift this off an
+d set $rl to 0 (XXX ostensibly to do straight reads).

We then determine what the console should be on various systems:

    Cygwin - We use stdin instead of a separate device.
    Windows or MSDOS - use con.
    AmigaOS - use CONSOLE:.
    VMS - use sys$command.
    Unix - use /dev/tty.

[download]

Question is: why on Unix con has a role?

And I find this in source of perl5db.pl:

elsif ( $^O eq 'dos' or -e "con" or $^O eq 'MSWin32' ) {
  $console = "con";
}

[download]

-e "con" short-circuits the Unix check further down (if file or dir "con" exists in current dir): if( -e '/dev/tty'). Surely a bug AFAICS.

bw, bliako

In reply to Re^2: perl -d myprog autostarts - but only in one specific directory by bliako
in thread perl -d myprog autostarts - but only in one specific directory by ibm1620

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