How to list files of a Debian package without install

This command can only list contents of installed packages,

dpkg -L PACKAGENAME

but how to list contents of a non-installed package, to preview/examine the package?

dpkg -c (or --contents) lists the contents of a .deb package file (It is a front-end to dpkg-deb.)

dpkg -c package_file.deb

To work directly with package names rather than package files, you can use apt-file. (You may need to install the apt-file package first.)

sudo apt-file update        
apt-file list package_name

As stated in the first comment, apt-file lists contents for packages in your already-configured Apt repositories. It is irrelevant whether any particular package is or is not installed.

Use --contents instead of -L:

dpkg --contents PACKAGENAME

When used in this manner, dpkg acts as a front-end to dpkg-deb, so use man dpkg-deb to see all the options.

You can also use an archive browser to view the package contents.

dpkg --contents will let you look at the uninstalled package. If the .deb is not on your system yet, do

apt-get --download-only install pkgname

The package will get downloaded to /var/cache/apt/archives but not installed.

The best way would be to browse directly the package repository:

http://packages.debian.org/[distro name]/all/[package name]/filelist

Example:

http://packages.debian.org/wheezy/all/transmission-common/filelist

I took @baldoz's http idea and generalized it for Ubuntu and Debian, added a little sed and wrapped it in a bash function one-liner:

function deb_list () { curl -s $(lsb_release -si | sed -e 's Ubuntu https://packages.ubuntu.com ' -e 's Debian https://packages.debian.org ')/$(lsb_release -sc)/all/$1/filelist | sed -n -e '/<pre>/,/<\/pre>/p' | sed -e 's/<[^>]\+>//g' -e '/^$/d'; }

Usage:

$ deb_list curl
/usr/bin/curl
/usr/share/doc/curl/changelog.Debian.gz
/usr/share/doc/curl/copyright
/usr/share/doc/curl/NEWS.Debian.gz
/usr/share/man/man1/curl.1.gz

Same function on multiple lines:

function deb_list () {
    curl -s $(lsb_release -si \
                | sed -e 's Ubuntu https://packages.ubuntu.com ' \
                      -e 's Debian https://packages.debian.org '
              )/$(lsb_release -sc)/all/$1/filelist \
      | sed -n -e '/<pre>/,/<\/pre>/p' \
      | sed -e 's/<[^>]\+>//g' -e '/^$/d';
}

Explained:

1. lsb_release -si returns "Ubuntu" or "Debian" replace that with the base url https://packages.ubuntu.com or https://packages.debian.org
2. lsb_Release -sc returns the codename (e.g. "trusty", "sid", etc) use that to build the full URL: https://packages.ubuntu.com/trusty/all/curl/filelist
3. Fetch that URL with curl and pipe the html through three sed commands. First captures only the file list (what's between <pre> and </pre> tags); second strips out any html tags; third removes any blank lines.

Note: It doesn't search PPAs, alternate apt sources repos and only queries official packages available for the release of debian/ubuntu you are running.