How can I find out if a specific program is installed?
there’s always apt-cache policy <package-name> (no sudo needed).
Not installed:
olivier@neews:/$ apt-cache policy gnuift gnuift: Installed: (none) Candidate: 0.1.14-11 Version table: 0.1.14-11 0 500 http://archive.ubuntu.com/ubuntu/ oneiric/universe amd64 Packages
Installed:
olivier@neews:/$ apt-cache policy firefox firefox: Installed: 8.0+build1-0ubuntu0.11.10.3 Candidate: 8.0+build1-0ubuntu0.11.10.3 Version table: *** 8.0+build1-0ubuntu0.11.10.3 0 500 http://archive.ubuntu.com/ubuntu/ oneiric-updates/main amd64 Packages 500 http://archive.ubuntu.com/ubuntu/ oneiric-security/main amd64 Packages 100 /var/lib/dpkg/status 7.0.1+build1+nobinonly-0ubuntu2 0 500 http://archive.ubuntu.com/ubuntu/ oneiric/main amd64 Packages
Or dpkg: dpkg -l | grep -E '^ii' | grep <package name>. When it’s not installed it won’t show output. When it is, it’ll show something like:
olivier@neews:~$ dpkg -l | grep -E '^ii' | grep firefox ii firefox 8.0+build1-0ubuntu0.11.10.3 Safe and easy web browser from Mozilla ii firefox-branding 8.0+build1-0ubuntu0.11.10.3 Safe and easy web browser from Mozilla - transitional package ii firefox-globalmenu 8.0+build1-0ubuntu0.11.10.3 Unity appmenu integration for Firefox ii firefox-gnome-support 8.0+build1-0ubuntu0.11.10.3 Safe and easy web browser from Mozilla - GNOME support ii firefox-locale-en 8.0+build1-0ubuntu0.11.10.3 English language pack for Firefox
It's obviously a fuzzier search but handy if you're not sure which package you're looking for. For manually installed things... A bit harder but if they're on the current path, you could just run them. That's a bit of mission so I'd rather just run: oli@bert:/$ which chromium-browser /usr/bin/chromium-browser
And:
oli@bert:/$ which gnuift # returns nothing
Which is better?
That depends on the sanity of user. There’s nothing to stop somebody installing something called chromium-browser that isn’t Chromium. They could even package it up incorrectly and install that. Neither method can be 100% certain.
But assuming the owner is sane – packages should be good enough for most people.