Making scripts executable (chmod +x) in Bash Scripting

Introduction

You need to tell your computer that a script is allowed to run as a program. This is done by making the script executable.

When you write a new script and want to run it directly.

When you download a script from the internet and want to use it.

When you share scripts with others and want them to run easily.

When automating tasks and the script must be run by the system.

When fixing permission errors that prevent scripts from running.

Syntax

Bash Scripting

chmod +x filename.sh

The command 'chmod' changes file permissions.

'+x' adds execute permission to the file for the user, group, and others.

Examples

Makes the script 'myscript.sh' executable so you can run it.

Bash Scripting

chmod +x myscript.sh

Adds execute permission to 'runme.sh' located in a folder.

Bash Scripting

chmod +x /home/user/scripts/runme.sh

Makes all files ending with '.sh' in the current folder executable.

Bash Scripting

chmod +x *.sh

Sample Program

This is a simple script that prints a message. After saving it as 'hello.sh', you make it executable with 'chmod +x hello.sh' and then run it with './hello.sh'.

Bash Scripting

#!/bin/bash

echo "Hello, this script is now executable!"

Important Notes

You must run './filename.sh' to execute the script in the current folder after making it executable.

If you forget to make a script executable, you will get a 'Permission denied' error when trying to run it.

You can check permissions with 'ls -l filename.sh' to see if the 'x' (execute) flag is set.

Summary

Use 'chmod +x filename' to allow running a script as a program.

Making a script executable is necessary before running it directly.

Check permissions with 'ls -l' to confirm execute rights.

Practice

1. What does the command chmod +x script.sh do in bash scripting?

easy

A. Makes the script script.sh executable so it can be run directly.

B. Deletes the script script.sh from the system.

C. Copies the script script.sh to another location.

D. Changes the owner of the script script.sh.

Solution

1. Step 1: Understand the chmod command

   The chmod command changes file permissions in Linux and Unix systems.

2. Step 2: Interpret the +x option

   The +x option adds execute permission, allowing the file to be run as a program.

3. Final Answer:

   Makes the script script.sh executable so it can be run directly. -> Option A

4. Quick Check:

   chmod +x means add execute permission [OK]

Hint: Remember +x means add execute permission [OK]

Common Mistakes:

• Confusing execute permission with deleting files
• Thinking chmod copies files
• Mixing up ownership change with permission change

2. Which of the following is the correct syntax to make a script named run.sh executable?

easy

A. chmod x run.sh

B. chmod x+ run.sh

C. chmod -x run.sh

D. chmod +x run.sh

Solution

1. Step 1: Recall the correct order of options in chmod

   The correct syntax to add execute permission is chmod +x filename.

2. Step 2: Check each option

   chmod +x run.sh matches the correct syntax exactly; others have incorrect order or missing symbols.

3. Final Answer:

   chmod +x run.sh -> Option D

4. Quick Check:

   Correct syntax is chmod +x filename [OK]

Hint: Use chmod +x filename to add execute permission [OK]

Common Mistakes:

• Placing + and x in wrong order
• Using -x which removes execute permission
• Omitting the + sign

3. Given a script hello.sh without execute permission, what will be the output of the command sequence below?

ls -l hello.sh
chmod +x hello.sh
ls -l hello.sh

medium

A. Both ls -l commands show execute permission.

B. The first ls -l shows no execute permission; the second shows execute permission added.

C. The first ls -l shows execute permission; the second removes it.

D. Both ls -l commands show no execute permission.

Solution

1. Step 1: Understand initial permissions

   Initially, hello.sh has no execute permission, so ls -l shows no 'x' in permissions.

2. Step 2: Apply chmod +x and check again

   After running chmod +x hello.sh, execute permission is added, so the second ls -l shows 'x' in permissions.

3. Final Answer:

   The first ls -l shows no execute permission; the second shows execute permission added. -> Option B

4. Quick Check:

   Adding +x updates permissions visible in ls -l [OK]

Hint: Check permissions before and after with ls -l [OK]

Common Mistakes:

• Assuming execute permission is present initially
• Thinking chmod +x removes execute permission
• Not noticing permission changes in ls -l

4. You try to run a script myscript.sh but get a "Permission denied" error. Which command fixes this issue?

medium

A. chmod -x myscript.sh

B. chmod +r myscript.sh

C. chmod +x myscript.sh

D. chmod 000 myscript.sh

Solution

1. Step 1: Identify cause of "Permission denied"

   The error usually means the script lacks execute permission.

2. Step 2: Add execute permission

   Using chmod +x myscript.sh adds execute rights, allowing the script to run.

3. Final Answer:

   chmod +x myscript.sh -> Option C

4. Quick Check:

   Add execute permission to fix "Permission denied" [OK]

Hint: Add execute permission with chmod +x [OK]

Common Mistakes:

• Using -x which removes execute permission
• Setting permissions to 000 which denies all access
• Adding only read permission (+r) which doesn't allow execution

5. You have a script deploy.sh that you want to run directly by typing ./deploy.sh. However, it still says "Permission denied" after chmod +x deploy.sh. What could be the reason?

hard

A. The script is on a mounted filesystem that does not support execute permissions.

B. You forgot to add read permission with chmod +r deploy.sh.

C. You need to rename the script to deploy.exe.

D. You must run the script with bash deploy.sh instead of ./deploy.sh.

Solution

1. Step 1: Confirm execute permission is set

   Since chmod +x deploy.sh was run, the script should have execute permission.

2. Step 2: Consider filesystem limitations

   Some mounted filesystems (like FAT32 or network shares) do not support Unix execute permissions, causing "Permission denied" despite chmod +x.

3. Step 3: Evaluate other options

   Adding read permission is usually default; renaming to .exe is irrelevant in Linux; running with bash works but does not explain the permission error when running ./deploy.sh.

4. Final Answer:

   The script is on a mounted filesystem that does not support execute permissions. -> Option A

5. Quick Check:

   Filesystem may block execute permission despite chmod [OK]

Hint: Check if filesystem supports execute permissions [OK]

Common Mistakes:

• Assuming chmod always works on all filesystems
• Thinking read permission alone allows execution
• Confusing script name extension with execution ability