PATH, FHS and $PS1 - Kim Schlesinger

This is a companion blog post for a presentation I gave at the February 2020 DenverScript Meetup.

You can find the video recording and slide deck on my talks page.

The Path Variable

PATH is an enviornment variable.
The variable is a colon-delimited string. The directory before each colon contains executable code and is invoked through a command, like pwd.
To see the value, run echo $PATH from your command line
Here’s an example path:
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
In the example, these are the directories in the path:
- /usr/local/sbin
- /usr/local/bin
- /usr/sbin
- /usr/bin
- /sbin
- /bin
When you type a text command and hit RETURN your computer looks in all the directories listed in the path, and if it finds code for the command, it will execute the program.
Most of the built-in system commands are written in the C programming langauge.
For MacOS and Linux, to change your path, find and edit it in your .bash_profile, .bashrc or .zshrc file.

I’ve learned alot about the PATH variable from Breanne Boland, who wrote the first two articles on this list.

The root directory contains folders and files under the forward-slash, /.
The Filesystem Hierarchy Standard defines the organization of the root directory.
Most Unix-like operating systems (UNIX, Linux, MacOS, etc.) organize their root directories according to the FHS.

A few directories in the root directory:

/bin: stands for binary, and contains common commands used by system adminstrators and users
/sbin: stands for system binaries, andontains root-only commands and commands that pair well with commands in /bin
/usr: has some read-only data, and lots of common commands in /usr/bin

PS1 is an enviornment variable that creates the default command prompt you see at the beginning of your command line.
To see the value, run echo $PS1.
Here’s an example PS1:
\u@\h:\w\$
In the example, the username (\u), hostname (\h) and working directory (\w) come before the dollar sign, and are separated by @ and :.
On my computer, this PS1 shows up as kschlesinger@kims-macbook-air:~$
To add colors to your PS1, open your bash_profile, .bashrc or .zshrc and add ANSI color escape sequences before each section of your PS1. Add an emoji if you’d like. Here’s an example:
export PS1="\[\033[36m\]\u\[\033[m\]@\[\033[32m\]\h:\[\033[33;1m\]\w\[\033[m\]\$ 🌵 "
On my computer, this PS1 shows up as kschlesinger@kims-macbook-air:~$ 🌵 with the username in teal, the hostname in green and the working directory in yellow.