Command-line arguments ($1, $2, ...) in Bash Scripting - Step-by-Step Execution

Concept Flow - Command-line arguments ($1, $2, ...)

Start script

↓

Read $1

↓

Read $2

↓

... Read $n

↓

Use arguments in script

↓

End script

The script starts and reads each command-line argument in order ($1, $2, ...), then uses them as needed before ending.

Execution Sample

Bash Scripting

#!/bin/bash

echo "First argument: $1"
echo "Second argument: $2"

This script prints the first and second command-line arguments passed to it.

Execution Table

Step	Action	Value of $1	Value of $2	Output
1	Start script	apple	banana
2	Print first argument	apple	banana	First argument: apple
3	Print second argument	apple	banana	Second argument: banana
4	End script	apple	banana

💡 Script ends after printing the first and second arguments.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
$1	unset	apple	apple	apple	apple
$2	unset	banana	banana	banana	banana

Key Moments - 2 Insights

Why does $1 hold the first argument and not the script name?

In bash, $0 holds the script name, while $1, $2, etc. hold the first, second, and subsequent arguments. See execution_table step 1 where $1 is 'apple' and not the script name.

What happens if I run the script without any arguments?

If no arguments are given, $1 and $2 are empty strings. The script will print 'First argument: ' and 'Second argument: ' with nothing after the colons, as no values are assigned.

Visual Quiz - 3 Questions

Look at the execution table, what is the output at step 2?

A First argument: apple

B Second argument: banana

C First argument: banana

D Second argument: apple

💡 Hint

Check the 'Output' column at step 2 in the execution_table.

At which step does the script print the second argument?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look at the 'Action' column to find when the second argument is printed.

If you run the script with no arguments, what will $1 be?

A The script name

B Error message

C Empty string

D The first argument typed previously

💡 Hint

Refer to key_moments about what happens when no arguments are passed.

Concept Snapshot

Command-line arguments in bash are accessed as $1, $2, etc.
$0 is the script name.
Arguments are strings passed after the script name.
Use them to customize script behavior.
If no argument is given, $n is empty.
Example: echo "$1" prints the first argument.

Full Transcript

This lesson shows how bash scripts use command-line arguments. The script reads arguments as $1, $2, and so on. $0 is reserved for the script name. The example script prints the first two arguments. The execution table traces each step: starting the script, printing $1, printing $2, and ending. Variables $1 and $2 hold the values passed when running the script. If no arguments are given, these variables are empty. Key moments clarify common confusions like why $1 is not the script name and what happens if no arguments are passed. The quiz tests understanding by asking about outputs and variable values at specific steps. The snapshot summarizes how to use command-line arguments in bash scripts.