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.
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'
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.
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.
