Open multiple pdfs in Okular from command line

mplayer comes with an midentify utility that does mostly what you want.

The output looks like variable assignments, so it is pretty easy to use in scripts/simple to parse.

If midentify isn't installed with your mplayer package, you might have an midentify.sh script in /usr/share/mplayer or something like that. If not, midenfify just runs mplayer with a specific set of arguments:

#!/bin/sh
#
# This is a wrapper around the -identify functionality.
# It is supposed to escape the output properly, so it can be easily
# used in shellscripts by 'eval'ing the output of this script.
#
# Written by Tobias Diedrich <ranma+mplayer@tdiedrich.de>
# Licensed under GNU GPL.

if [ -z "$1" ]; then
        echo "Usage: midentify.sh <file> [<file> ...]"
        exit 1
fi

mplayer -vo null -ao null -frames 0 -identify "$@" 2>/dev/null |
    sed -ne '/^ID_/ {
                      s/[]()|&;<>`'"'"'\\!$" []/\\&/g;p
                    }'

The -ao, -vo and -frames parameters prevent mplayer from actually playing the clip. The rest is just formatting.

Example:

$ midentify some_random.avi 
ID_VIDEO_ID=0
ID_AUDIO_ID=0
...
ID_VIDEO_BITRATE=258488
ID_VIDEO_WIDTH=320
ID_VIDEO_HEIGHT=240
ID_VIDEO_FPS=29.917
...
ID_LENGTH=4216.76
...
ID_AUDIO_BITRATE=64000
ID_AUDIO_RATE=22050
...

A file manager is responsible for invoking applications to open a file. It has no control over what the application does with the file, and in particular whether the application will open a new window if you open the same file twice.

Having the same file open in multiple windows can be useful, for example when you want to see different sections from the same document. So systematically refusing to open more than one window on the same document would be bad. Which behavior is the default is mostly a matter of taste. Some applications default to opening a new window, others default to focusing the existing window.

Okular defaults to opening a new window. If you start all instances with okular --unique, then the second time you run that command, it doesn't open a new window (though it doesn't focus the existing window, at least if you aren't running KDE). Note that the first instance must have been started with --unique as well as the second one.

Evince, the Gnome PDF viewer, defaults to the behavior you want: if you open the same document a second time, it focuses the existing window. It doesn't have a command line option to open a separate window, you have to do this through the GUI (menu “File” → “Open a Copy” or Ctrl+N).