## Installing gcc 4.8 and Linuxbrew on CentOS 6

The GCC distributed with CentOS 6 is 4.4.7, which is pretty outdated. I'd like to use gcc 4.8+. Also, when trying to install [Linuxbrew](https://github.com/Homebrew/linuxbrew) you run into a dependency loop where Homebrew's gcc depends on zlib, which depends on gcc. Here's how I solved the problem.

_Note_: Requires `sudo` privileges. 

### Resources:

- <http://superuser.com/a/676337/88393>: Forum response on using CERN's open Scientific Linux distribution of RHEL's developer toolset.
- <http://linux.web.cern.ch/linux/devtoolset/>: CERN's developer toolset installation instructions.
- <https://github.com/Homebrew/linuxbrew/wiki/Standalone-Installation>: Instructions for a standalone installation of Homebrew. 
- <https://twitter.com/sjackman>: Shaun Jackman -- the hero who maintains Linuxbrew.

### Upgrading gcc

First, verify which version of CentOS you're using:

```
$ cat /etc/centos-release
CentOS release 6.7 (Final)
```

Import CERN's GPG key:

```
sudo rpm --import http://ftp.scientificlinux.org/linux/scientific/5x/x86_64/RPM-GPG-KEYs/RPM-GPG-KEY-cern
```

Save repository information as `/etc/yum.repos.d/slc6-devtoolset.repo` on your system:

```
wget -O /etc/yum.repos.d/slc6-devtoolset.repo http://linuxsoft.cern.ch/cern/devtoolset/slc6-devtoolset.repo
```

Install:

```
sudo yum install devtoolset-2
```

Enable the environment: 

```
scl enable devtoolset-2 bash

```

Test the environment: 

```
$ gcc --version
gcc (GCC) 4.8.2 20140120 (Red Hat 4.8.2-15)
...

$ g++ --version
g++ (GCC) 4.8.2 20140120 (Red Hat 4.8.2-15)
...

$ gfortran --version
GNU Fortran (GCC) 4.8.2 20140120 (Red Hat 4.8.2-15)
...
```

_Optional_: Permanently enable scl toolchain by putting this in your `.bashrc` (warning: don't try to use the `scl enable devtoolset-2 bash` command from before in your .bashrc. This spawns a new bash shell, and if that's in your .bashrc, it creates a new shell, which loads your .bashrc, which creates a new shell, etc.)

```
source /opt/rh/devtoolset-2/enable
```

### Installing Linuxbrew

Enable the SCL environment:

```
scl enable devtoolset-2 bash

```

Create symlinks to your new gcc/g++/gfortran:

```
ln -s $(which gcc) `brew --prefix`/bin/gcc-$(gcc -dumpversion |cut -d. -f1,2)
ln -s $(which g++) `brew --prefix`/bin/g++-$(g++ -dumpversion |cut -d. -f1,2)
ln -s $(which gfortran) `brew --prefix`/bin/gfortran-$(gfortran -dumpversion |cut -d. -f1,2)
```

Install Linuxbrew:

```
ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/linuxbrew/go/install)"
```

Add these to your `.bashrc`, and source it:

```
export PATH="$HOME/.linuxbrew/bin:$PATH"
export MANPATH="$HOME/.linuxbrew/share/man:$MANPATH"
export INFOPATH="$HOME/.linuxbrew/share/info:$INFOPATH"
```

Test your installation:

```
brew install hello
brew test hello
brew remove hello
```