stdin - default file source for <> in perl -

i want read data <> operator.

it reads data stdin or files specified script's args

but, if no stdin presented, nor file specified, want read data default file path;

so, should

my $file = ''; if ($argc) { open $file, '<default.txt'; } while (<$file>)  # if no args should <> {    do_all; } 

the <> operator reads list of input file names @argv. thus, 1 way set default input file name check if @argv empty, , if so, push default file name onto it:

push @argv, "default.txt" unless @argv; 

---

i'm not sure mean "no stdin presented", if mean want script read foo.txt instead of default.txt if invoked e.g.:

perl script.pl < foo.txt 

or:

cat foo.txt | perl script.pl 

then checking whether stdin reading terminal or not, using -t file test. if stdin not tty, pipe or file, , should try read it:

push @argv, "default.txt" unless @argv or !-t stdin;