Examples not working?

CentOS Software Collections (SCL) #

Software Collections (SCL) is a CentOS repository that provides a set of dynamic programming languages, database servers, and various related packages. Provided software versions are […] more recent than their equivalent versions included in the base CentOS distribution […] Packages available from the SCL […] can be optionally enabled per application by using supplied scl utility.

Available SCLs and their Packages #

To list all Software Collections installed on the development nodes, use:

[alice@c4-dev1 ~]$ scl --list
devtoolset-10
devtoolset-11
devtoolset-7
devtoolset-8
devtoolset-9
httpd24
llvm-toolset-7
rh-perl526
rh-python36
rh-python38
rh-ruby25
rh-ruby26

To list all the packages that are part of one or more of these SCLs, use:

[alice@c4-dev1 ~]$ scl --list rh-ruby26
$ scl --list rh-ruby26
rh-ruby26-rubygem-bson-doc-4.3.0-1.el7.noarch
rh-ruby26-ruby-devel-2.6.2-118.el7.x86_64
...
rh-ruby26-rubygem-test-unit-3.2.9-118.el7.noarch

Using SCLs #

Interactive use #

Neither the Ruby interpreter ruby nor the Ruby interactive irb tool is part of the core-software installation. For example, if we would try to run ruby, we would get an error:

[alice@c4-dev1 ~]$ ruby --version
-bash: ruby: command not found

However, as we saw above, Ruby is available through an SCL. For interactive work, the most natural way to use an SCL is maybe to launch a new shell (typically Bash) with the SCL enabled:

[alice@c4-dev1 ~]$ scl enable rh-ruby26 $SHELL

[alice@c4-dev1 ~]$ ruby --version
ruby 2.6.2p47 (2019-03-13 revision 67232) [x86_64-linux]

[alice@c4-dev1 ~]$ irb
irb(main):001:0> 1+2
=> 3
irb(main):002:0> exit

[alice@c4-dev1 ~]$

With this approach, ruby and irb behave as if they were part of the core software installation.

How to disable the SCL? Above, we are actually launching another shell on top of the one we where already running. The only difference is that the second shell is running with the SCL enabled. Just like we can exit any shell by calling exit or logout, we can “unload” the enabled SCL and return to the previous shell by calling exit, i.e.

[alice@c4-dev1 ~]$ exit

[alice@c4-dev1 ~]$ ruby --version
-bash: ruby: command not found

An alternative approach to running the SCL-based Ruby, is to launch it directly instead of via the intermediate SCL-enabled shell. For example, we can run a Ruby script as:

[alice@c4-dev1 ~]$ scl enable rh-ruby26 ruby hello.rb
Hello world!

or launch the interactive Ruby tool as:

[alice@c4-dev1 ~]$ scl enable rh-ruby26 irb
irb(main):006:0> puts "Hello world!";
Hello world!
=> nil
irb(main):007:0> exit
[alice@c4-dev1 ~]$

Using SCLs in scripts #

To use SCL-based software in script, including job scripts, we need to use the “direct” SCL approach as mentioned above. Here is an example script that outputs the current timestamp and then runs two Ruby scripts after each other:

#!/usr/bin/env bash

echo "Started on: $(date --rfc-3339=seconds)"
scl enable rh-ruby26 ruby hello.rb
scl enable rh-ruby26 ruby main.rb

See Also #