use open ':std', OUT => ':utf8';
use constant TIMEOUT  => 3;
use constant MAXTRIES => 30;
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./4.triton.pl: line 1: use: command not found
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3:              empty
30:             empty
:utf8:          empty
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By itself, Linux can only run ELF executables and text files containing a special header with a path to the interpreter (but see also binfmt_misc). When you try to run a file that's neither of there two things, the shell makes one last try to run a text file as a shell script. (If it wasn't a text file, you would get cannot execute binary file: Exec format error instead. I'm not sure how shell discerns between these two, but I think that it looks for null bytes.)

If you paste use open ':std', OUT => ':utf8'; in the shell, you would, indeed, get use: command not found and a new empty file named :utf8.

The solution would be to either add a #!/usr/bin/perl (or #!/usr/bin/env perl, whichever is more appropriate for your system) as the first line of the script or to run the script using perl 4.triton.pl instead.