Making scripts executable (chmod +x) in Bash Scripting - Step-by-Step Execution

Concept Flow - Making scripts executable (chmod +x)

Write script file

↓

Check file permissions

↓

Run: permission denied?

Yes→Use chmod +x to add execute permission

↓

File now executable

↓

Run script successfully

This flow shows how a script file is made executable by adding execute permission with chmod +x, allowing it to run without permission errors.

Execution Sample

Bash Scripting

#!/bin/bash
# hello.sh
echo "Hello, world!"

This script prints 'Hello, world!'. We add execute permission with chmod +x, then run it.

Execution Table

Step	Command	File Permission Before	Action	File Permission After	Output
1	ls -l hello.sh	-rw-r--r--	Check permissions	-rw-r--r--
2	./hello.sh	-rw-r--r--	Try to run script	-rw-r--r--	bash: ./hello.sh: Permission denied
3	chmod +x hello.sh	-rw-r--r--	Add execute permission	-rwxr-xr-x
4	ls -l hello.sh	-rwxr-xr-x	Verify permissions	-rwxr-xr-x
5	./hello.sh	-rwxr-xr-x	Run script	-rwxr-xr-x	Hello, world!

💡 Execution stops after successful script run with execute permission.

Variable Tracker

Variable	Start	After Step 1	After Step 3	After Step 5
File Permission	N/A	-rw-r--r--	-rwxr-xr-x	-rwxr-xr-x
Script Output	N/A	N/A	N/A	Hello, world!

Key Moments - 3 Insights

Why does the script give 'Permission denied' before using chmod +x?

Because the file lacks execute permission (-rw-r--r--), so the system blocks running it. See execution_table step 2.

What does chmod +x actually do to the file permissions?

It adds execute permission for user, group, and others, changing -rw-r--r-- to -rwxr-xr-x as shown in step 3.

Why can we run the script after chmod +x but not before?

Because only after adding execute permission does the system allow running the file as a program, shown by successful output in step 5.

Visual Quiz - 3 Questions

Look at the execution table, what is the file permission after step 1?

A -rw-r--r--

B -rwxr-xr-x

C -r--r--r--

D -rw-rw-rw-

💡 Hint

Check the 'File Permission After' column in step 1.

At which step does the script become executable?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Look at the 'Action' and 'File Permission After' columns to see when execute permission is added.

If we skip chmod +x, what output do we get when running ./hello.sh?

A Hello, world!

B Permission denied

C No such file or directory

D Syntax error

💡 Hint

See step 2 output in the execution table.

Concept Snapshot

chmod +x filename
- Adds execute permission to a script file
- Changes permissions from non-executable to executable
- Allows running script with ./filename
- Without +x, running script gives 'Permission denied'
- Check permissions with ls -l

Full Transcript

This lesson shows how to make a script file executable using chmod +x. Initially, the script file has no execute permission, so trying to run it results in 'Permission denied'. Using chmod +x adds execute permission, changing the file mode to allow running it. After this, running the script prints the expected output. The execution table traces each step: checking permissions, trying to run, adding execute permission, verifying permissions, and running successfully. Key moments clarify why permission denied happens and what chmod +x does. The quiz tests understanding of permission states and effects of chmod +x.