90 lines
2.5 KiB
Markdown
90 lines
2.5 KiB
Markdown
---
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tags:
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- shell
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---
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# The `$PATH`
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We know that `$PATH` is an
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[environment variable](Environmental_and_shell_variables.md).
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This variable keeps track of directories **where executables are found**.
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Whenever any command is run, the shell looks up the directories contained in the
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`PATH` for the target executable file and runs it. We can see this is the case
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by using the `which` command which traces the executable of bash commands. Take
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the `echo` program:
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```bash
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which echo
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# echo: shell built-in command
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```
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Or `npm` :
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```bash
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which npm
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/home/thomas/.nvm/versions/node/v19.4.0/bin/npm
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```
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By default the path will always contain the following locations:
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- `/usr/bin`
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- `/usr/sbin`
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- `/usr/local/bin`
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- `/usr/local/sbin`
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- `/bin`
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- `/sbin`
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All the inbuilt terminal programs reside at these locations and most of them are
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at `/usr/bin`. This is why they run automatically without error. If you attempt
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to run a program that doesn’t reside at these locations then you will get an
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error along the lines of `program x is not found in PATH`.
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## Structure of the PATH
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```bash
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/home/thomas/.nvm/versions/node/v19.4.0/bin:
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/usr/local/sbin:/usr/local/bin:/usr/bin:/usr/lib/jvm/default/bin:
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/usr/bin/site_perl:/usr/bin/vendor_perl:/usr/bin/core_perl
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```
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## Adding to the PATH
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Only the default directories load to the PATH on every session. How then can we
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add custom directories to the path without them being lost every time we start a
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new session? Remember that the user config `.bashrc` loads on init for every
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bash session. Therefore, if we set the custom path in this file, it will be
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created every time we start a session. This is why when you add a new program it
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often ask you to append a script to the bottom of your `.bashrc` .
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For example, at the bottom of my `.zshrc` on my work computer I have:
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```bash
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export CHROME_BIN=/mnt/c/Program\\ Files\\ \\(x86\\)/Google/Chrome/Application/chrome.exe
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```
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This enables me to access the Chromium binaries from my terminal session (needed
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for running Angular tests) but it doesn’t add it to the path, it creates an
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environment variable on every session.
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For demonstration, let’s add a user’s desktop directory to the PATH.
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First we go to the `.bashrc` and add the `export` command. Remember that this is
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the command for creating a new environment variable:
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```bash
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export PATH="$PATH=:~/Desktop"
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```
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We force a reload of the `.bashrc` with the command:
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```bash
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source ~/.bashrc
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```
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Then we can check this directory has been added to the path with an echo
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```bash
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echo $PATH
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...:~/Desktop
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```
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