Environment variables vs local variables in Bash Scripting - Visual Side-by-Side Comparison

Concept Flow - Environment variables vs local variables

Start Script

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Set local variable

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Set environment variable (export)

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Call child process

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Child sees environment variable

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Child does NOT see local variable

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End Script

This flow shows how local variables exist only in the current script, while environment variables (exported) are passed to child processes.

Execution Sample

Bash Scripting

name="local"
export city="NewYork"
echo "Local: $name"
echo "Env: $city"
bash -c 'echo "Child sees city: $city"; echo "Child sees name: $name"'

This script sets a local variable and an environment variable, then runs a child bash to show which variables are visible.

Execution Table

Step	Action	Variable 'name'	Variable 'city'	Output
1	Set local variable name="local"	local	unset
2	Export environment variable city="NewYork"	local	NewYork
3	Print local variable	local	NewYork	Local: local
4	Print environment variable	local	NewYork	Env: NewYork
5	Run child bash to print variables	local (not passed)	NewYork (passed)	Child sees city: NewYork Child sees name:

💡 Script ends after child process runs; local variable not passed, environment variable passed.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 5 (child)
name	unset	local	local	unset (not visible)
city	unset	unset	NewYork (exported)	NewYork (visible)

Key Moments - 2 Insights

Why does the child bash see the environment variable 'city' but not the local variable 'name'?

Because only variables exported with 'export' become environment variables visible to child processes, as shown in execution_table step 5 where 'city' is visible but 'name' is empty.

Does setting a variable without 'export' make it available to child processes?

No, local variables are only available in the current shell or script. The execution_table step 5 shows the child process cannot see 'name' because it was not exported.

Visual Quiz - 3 Questions

Look at the execution_table at step 3, what is the output?

A Local: NewYork

B Local: local

C Local:

D Local: name

💡 Hint

Check the 'Output' column at step 3 in the execution_table.

At which step does the variable 'city' become visible to the child process?

A Step 1

B Step 3

C Step 5

D Step 2

💡 Hint

Look at the 'Variable city' column and output at step 5 in the execution_table.

If we remove 'export' from the city variable, what happens in the child process output?

A Child sees city:

B Child sees name: local

C Child sees city: NewYork

D Child sees both variables

💡 Hint

Refer to variable_tracker and execution_table step 5 showing visibility depends on export.

Concept Snapshot

Local variables exist only in the current shell or script.
Environment variables are local variables marked with 'export'.
Only environment variables are passed to child processes.
Use 'export VAR=value' to make a variable visible to child processes.
Without export, variables remain local and invisible outside.
Child processes inherit environment variables but not local variables.

Full Transcript

This lesson shows the difference between local and environment variables in bash scripting. A local variable is set normally and exists only in the current shell. An environment variable is created by exporting a local variable with 'export'. When a child process runs, it can see environment variables but not local variables. The example script sets a local variable 'name' and exports 'city'. The child bash process prints both variables. It sees 'city' but not 'name'. This shows that only exported variables are passed down. Understanding this helps control variable visibility in scripts and subprocesses.