25 minv1.0

Users, groups and environment

Learning objectives

Explain shell variables and exported environment variables, inspect PATH, and configure a temporary project variable safely.

1 Objective→ 2 Learn→ 3 Example→ 4 Practice→ 5 Verify→ 6 Continue

How to study this lessonUnderstand the idea first. Use the example to see the behaviour, practise where provided, then make sure you can explain the result before continuing.

Explanation

Variables and child processes

A shell variable exists in the current shell. export places it in the environment inherited by commands started from that shell. This is how EDA setup scripts provide paths and license or tool settings to simulators.

PATH is an ordered list of directories searched for executable commands. Use command -v tool to see what will run. Do not place the current directory or an untrusted writable directory before trusted system directories.

Commands you will use

Command	What it does	Example
`env`	Prints exported environment variables.	`env`
`printenv`	Prints one exported value.	`printenv PATH`
`export`	Exports a variable to child processes.	`export PROJECT_HOME="$HOME/project"`
`unset`	Removes a variable from the current shell.	`unset PROJECT_HOME`
`command -v`	Shows the executable selected through `PATH`.	`command -v python3`
`type`	Explains whether a name is an executable, alias, function, or built-in.	`type cd`
`source`	Runs a trusted setup file in the current shell.	`source tools/setup.sh`
`alias`	Defines an interactive shortcut.	`alias ll='ls -lh'`

Startup files such as .bash_profile and .bashrc can make settings persistent. Test a setting in the current shell before changing a startup file. Never store passwords or tokens in shell history or course evidence.

Worked example

mkdir -p "$HOME/asic-linux-practice/project"
PROJECT_HOME="$HOME/asic-linux-practice/project"
printf 'current shell: %s\n' "$PROJECT_HOME"
sh -c 'printf "before export: %s\n" "$PROJECT_HOME"'
export PROJECT_HOME
sh -c 'printf "after export: %s\n" "$PROJECT_HOME"'
command -v bash
type cd
unset PROJECT_HOME

Expected result: the first child shell sees an empty value; after export, the next child shell receives the project path.

Common mistakes

Writing a change to .bashrc before testing it.
Appending the same directory to PATH every time a setup script runs.
Sourcing an unknown script.
Printing secrets while collecting environment evidence.
Using a broad LD_LIBRARY_PATH change instead of identifying the required library.

Check yourself

Why can a child process read an exported variable but not an ordinary shell variable?

Engineering practice

Practice: Users, groups and environment

Task→Run / reason→Check result→Explain why

Export PROJECT_HOME, start a child Bash process that prints it, then unset it. Record the executable path and version of one available engineering tool.

Practice work is non-certified and is not stored by ASIC Campus.