How do I use filenames that start with a dash "-" as command arguments?

This may be a simple question, but how do I use files starting with "-" with command line programs?

For example, I am trying to use pdfgrep on a file named -2013-01-01.pdf but it complains that there are no options defined for 2, 0, 1, 3 and so on.

Changing the filename to something that does not start with "-" solves it, but this is not an option since the files aren't created by me. I simply want to check for a specific change I know is coming.

Very frequently -- is used on the command-line to signal to a program that no more available command switches are going to be used. This is particularly useful if a file contains a dash, which the program would try to interpret as an option.

1. Without the --, there is an error generated:

   $ pdfgrep -i posix -find.pdf -xorg.pdf
   
   pdfgrep: invalid option -- 'f'
   pdfgrep: invalid option -- 'd'
   pdfgrep: invalid option -- '.'
   pdfgrep: invalid option -- 'p'
   pdfgrep: invalid option -- 'd'
   pdfgrep: invalid option -- 'f'
   

2. With the -- used we have a successful command:

   $ pdfgrep -i posix -- -find.pdf -xorg.pdf
   
   -find.pdf: on the command line. Currently-implemented types are emacs (this is the default), posix-awk,
   -find.pdf: posix-basic, posix-egrep and posix-extended.
   -find.pdf: posix-basic, posix-egrep and posix-extended.
   -find.pdf: posix-basic, posix-egrep and posix-extended.
   

3. pdfgrep is programmed to understand -- to mean that the following command-line arguments are not options. Most programs do the same, but not all programs understand --. For programs that don't, the solution is to prepend the filename with ./, like this:

    pdfgrep -i posix ./-find.pdf ./-xorg.pdf
   

   This should work with any command, unless for some reason the command cannot accept a path, only a pure filename.

For a general introduction to the command-line, see this useful PDF.

You prepend the file name with ./ (or another relative or absolute path that works). This way it's portable.

Example:

for zefile in ./*.tmp
do
   rm -f "$zefile"
done

The use of -- to indicate the end of options is not always available. Some commands will know it, some won't. And this will change across different systems. So in the end, it's less portable.