pass all files in directory as one argument to perl script

The feature that you are looking for is handled by the shell. It is called pathname expansion. For example, suppose that you are in a directory that contains the files file1 file2 file3 .. file50. You can specify all the files in the directory that start with file as an argument to to your perl script via:

./perl_script.pl file*

To the shell, * means zero or move of any characters. The shell looks for all files whose names start with file and are followed by zero or more of any character. Further, if you want to specify all files from the current directory:

./perl_script.pl *

If you want to specify all files in some other directory, use:

./perl_script.pl /some/other/dir/*

Note that this is a shell feature, not a perl feature. The shell does the pathname expansion before the argument list is passed to perl. Consequently, it will work will any shell command. If you want to test out pathname expansion without actually running the perl script, you can simply use echo:

echo /some/other/dir/*

This will show the same results of the pathname expansion that the perl script would see.

Special Cases

By default, if there is no file matching your pattern, then the pattern itself is returned:

$ echo *bash*
*bash*

Under bash, this behavior can be changed with the nullglob and globfail options.

Also, files whose names start with a period are, by default, not included in pathname expansions. They will be included, however, if you specify a pattern that begins with a period:

$ echo .*bash*
.bash_history .bash_logout .bash_profile .bashrc

More Features

In addition to *, there is the special character ? which means any one character. Thus file? would expand to file1 but not file10.

It is also possible to specify groups of characters. Thus, file[123] would expand, assuming they exist, to files file1, file2, file3 but not file4. file[[:digit:]] expands to all files whose names consist of file followed by one, and only one, digit.

Advanced shells, like bash, have many more options. Read about them under "pathname expansion" in man bash.