1654: Universal Install Script
|Universal Install Script|
Title text: The failures usually don't hurt anything, and if it installs several versions, it increases the chance that one of them is right. (Note: The 'yes' command and '2>/dev/null' are recommended additions.)
Most users of computers today are used to simple, easy installation of programs. You just download a .exe or a .dmg, double click it, and do what it says. Sometimes you don't even have to install anything at all, and it runs without any installation.
However, when things are more "homebrew", for example downloading source code, things are more complicated. Under Unix-like systems, which this universal install script is designed for, you may have to work with "build environments" and "makefiles", and command line tools. To make this process simpler, there exist repositories of programs which host either packages of source code and the things needed to build it or the pre-built programs. When you download the package, it automatically does most of the work of building the code into something executable if necessary and then installing it. However, there are many such repositories, such as "pip" and "brew", among others listed in the comic. If you only know the name of a program or package, you may not know in which repository(ies) it resides.
The script provided in the comic attempts to fix this problem, by giving a "universal install script", which contains a lot of common install commands used in various Unix-like systems. In between each of the install commands in the script is the & character, which in POSIX-compatible shells (including Bash, a popular shell scripting language) means it should continue to run the next command without waiting for the first command to finish, and not print any output of the command other than errors. This has the effect of running all the install commands simultaneously; whatever errors each commands would have because of a package not existing in that repository will be mixed together as they are all displaying on the screen around the same time. More about the & below.
The script accepts the name of a program when you run it as an argument. This value is then referenced as "$1" (argument number 1). Everywhere the script says "$1", it substitutes in the name of the package you gave it. The end result is the name being tried against a large number of software repositories and package managers, and hopefully, at least one of them will be appropriate and the program will be successfully installed. Near the end, it even tries changing the current working directory to that which is assumed to hold the package to be installed, and then runs several commands which build the program from source code.
All in all, this script would probably work; it runs many standard popular repository programs and package managers, and runs the nearly-universal commands needed to build a program. Most of the commands would simply give an error and exit, but hopefully the correct one will proceed with the install.
One of the more subtle jokes in the comic is the inclusion of
sudo apt-get in the same script. In most cases this would be redundant as the
sudo command is just to add admin permissions. This could be an allusion to a joke in the Linux community about forgetting to include the sudo command. An example of this joke being used elsewhere was a viral tweet that showed a workaround for the issue. Sudo has also been used both by Randall in 149: Sandwich and by Jason Fox to force Randall to let him appear on xkcd with 824: Guest Week: Bill Amend (FoxTrot).
Another explanation for this could be that plain "apt-get" is for Debian, while Ubuntu etc. use sudo.
curl downloads files from the network (e.g., the Internet). Used like
curl http://xkcd.com/ it downloads the xkcd main page and displays the HTML source code. The pipe
| in the script attaches the output of the command before the pipe to the input of the command after the pipe. Both commands are executed concurrently. Bash is a popular shell for Unix-like operating systems. The line
curl "$1" | bash tries to download a file from the network and to execute the download directly.
The use of & at the end of each line causes the shell interpreter to execute the commands in parallel (asynchronously) instead of sequentially. Even if single commands fail, the rest of them will be executed. Note this is even the case for the final commands which attempt to change to the installed package, probably the only reason why this may not work completely for packages that do need compiling after being downloaded. (However, just running this script again would probably do the trick.)
There appears to be a bug with the & at the end of the "git clone" line; since a git repository typically contains program source code, not executables, it may have been intended to retrieve the source code with git and then compile and install the program in the next line. In this case, the single & should be replaced with &&, an operator that will run the second command only if the first one has completed successfully. This plays into a second bug on the "configure" line, where the placement of the & means that only the "make install" command will be run asynchronously after the "configure" and "make" steps have finished in sequence. To make success as likely as possible, the two lines should be like this:
git clone https://github.com/"$1"/"$1" && (cd "$1"; ./configure; make; make install) &
The title text mentions the possibility that the same program may be in multiple repositories, so in this case, the script will download and install several versions, or it may fail on a number of repositories, in which case usually nothing bad happens. Since all the commands come from different operating systems, versions, or distributions, it is not very likely that more than one will work (with the exception of pip/easy_install and the two forms of apt-get) or even exist on the same system. It mentions that adding a way of automatically saying "yes" to questions asked during the different repository-fetching programs' running, by making them read input from another program that writes a (nearly) endless stream of "y"s, could simplify things further.
2>/dev/null redirects the second output stream (the "error stream") to the null device driver, which discards all writes to it, meaning errors (the package not existing) will be ignored.
- [In the panel is a shell script which, unusual for xkcd, uses only lower case. At the top the title of the program is inlaid in the frame, which has been broken here.]
- pip install "$1" &
- easy_install "$1" &
- brew install "$1" &
- npm install "$1" &
- yum install "$1" & dnf install "$1" &
- docker run "$1" &
- pkg install "$1" &
- apt-get install "$1" &
- sudo apt-get install "$1" &
- steamcmd +app_update "$1" validate &
- git clone https://github.com/"$1"/"$1" &
- cd "$1";./configure;make;make install &
- curl "$1" | bash &
- pip and easy install are package managers for Python
- brew is the successor/replacement for MacPorts and a package manager for OS X
- npm is the node package manager that maintains node.js packages
- yum is the package management tool for Red Hat Enterprise Linux and some derivatives.
- dnf is the package management tool for Fedora since version 22.
- docker run is an Amazon Web Services command that "Specifies one or more commands that install packages and configure your web application inside the [AWS] image." (http://docs.aws.amazon.com/elasticbeanstalk/latest/dg/create_deploy_docker_image.html)
- pkg is the package management tool on BSD systems
- apt-get is the package management tool of Debian and derivatives (eg Ubuntu)
- steamcmd refers to Steam, the computer game client
- git is the revision control software used for eg. the linux kernel and gained a lot of traction through the github plattform
- configure/make/make install refers to the default way of compiling software from source (on Linux/Unix)
- curl is a tool for loading data via http:// (eg from a website), this data is then pushed to the shell interpreter (in order to install).
- Note: While this is a security nightmare, the Nvidia drivers for Linux were (but no longer are) installed like that
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