what is the difference between which gcc and dpkg -l | grep gcc

Question

based on Ubuntu 12.04 man page for which

which returns the pathnames of the files (or links) which would be exe- cuted in the current environment, had its arguments been given as com- mands in a strictly POSIX-conformant shell. It does this by searching the PATH for executable files matching the names of the arguments. It does not follow symbolic links.

I also know that if you want to make sure you have installed a program, you can type dpkg -l | grep myprogram.

Recently, I downloaded gcc41 and g++41 from a deb package. I installed them with the following command : sudo dpkg -i gcc41-compat-4.1.2_i386.deb g++41-compat-4.1.2_i386.deb.

My problem is that when I type dpkg -l | grep gcc I see this

ii  gcc                                    4:4.6.3-1ubuntu5                        GNU C compiler
ii  gcc-4.5                                4.5.3-12ubuntu2                         The GNU C compiler
ii  gcc-4.5-base                           4.5.3-12ubuntu2                         The GNU Compiler Collection (base package)
ii  gcc-4.6                                4.6.3-1ubuntu5                          GNU C compiler
ii  gcc-4.6-base                           4.6.3-1ubuntu5                          GCC, the GNU Compiler Collection (base package)
ii  gcc41-compat                           4.1.2                                   No description
ii  libgcc1                                1:4.6.3-1ubuntu5

As you can see, gcc41-compat is installed, but when I type which gcc41 there is not any result. Based on the man page that I mentioned above, I should see something. Where is it? Or which part of my conclusion is wrong?

Answer 1

• which

  which gives location of binary installation directory. It is used as which <pkgname>

  So the command

  which gcc
  

  gives

  /usr/bin/gcc
  

• dpkg -i

  dpkg -i is used for installation.It has nothing to do with finding a package directory.

• dpkg -l

  dpkg -l is used to find if a package is installed or not.dpkg -l <pkgname> will give you an output with names of installed packages matching the given name.dpkg -l gives list of all packages.

• write

  It is used to send message to other user.

  I can't tell why you used this one.

• grep

  to show only the relevant part of the output.it is useful when piping commands.

---

1. If you want to find if gcc is installed, the best shot for you would be to use

   dpkg -l|grep gcc
   

   This will show all packages(installed) containing gcc in it's name,

   You could also use dpkg -l gcc but it gives output showing only those packages which contain only gcc.

2. If you want to check the location of the gcc binary that is in your $PATH, try

   which gcc
   

   Though there are few others too.