Making scripts executable (chmod +x) in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this command sequence?

You have a script named myscript.sh without execute permission. You run these commands:

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

What changes will you see in the second ls -l output compared to the first?

Bash Scripting

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

A The file permissions will show an 'x' for the user, group, and others indicating execute permission.

B The file size will increase because execute permission adds bytes to the file.

C The file owner will change to root after running chmod +x.

D The file name will change to myscript.sh.exe after adding execute permission.

💡 Hint

Think about what the 'x' means in file permissions and what chmod +x does.

The chmod +x command adds execute permission to the file for user, group, and others. This is shown as 'x' in the permission string when you run ls -l. It does not change file size, owner, or name.

📝 Syntax

intermediate

Which command correctly makes a script executable for the owner only?

You want to make a script named run.sh executable only by the file owner, not by group or others. Which command achieves this?

A chmod +x run.sh

B chmod a+x run.sh

C chmod u+x run.sh

D chmod og+x run.sh

💡 Hint

Remember that 'u' means user (owner), 'g' group, 'o' others, and 'a' all.

chmod u+x adds execute permission only for the user (owner). chmod +x or chmod a+x adds execute permission for all (user, group, others). chmod og+x adds execute for group and others, not user.

🔧 Debug

advanced

Why does this script fail to run even after chmod +x?

You have a script script.sh with execute permission set by chmod +x script.sh. When you run ./script.sh, you get bash: ./script.sh: /bin/bash^M: bad interpreter: No such file or directory. What is the cause?

A The script is missing the .sh extension.

B The script has Windows-style line endings causing the ^M character in the shebang line.

C The script file is empty and cannot run.

D The script does not have execute permission for the user.

💡 Hint

The ^M character often appears when files are edited on Windows and run on Linux.

The ^M character is a carriage return from Windows line endings (CRLF). Linux expects LF only. This causes the interpreter path to be invalid. Converting the file to Unix line endings fixes this.

🚀 Application

advanced

How to make all scripts in a folder executable for the owner only?

You have many scripts in a folder scripts/. You want to make all files ending with .sh executable only by the owner. Which command will do this correctly?

A chmod +x scripts/*.sh

B chmod a+x scripts/*.sh

C chmod og+x scripts/*.sh

D chmod u+x scripts/*.sh

💡 Hint

Think about which users should get execute permission and how to specify that in chmod.

chmod u+x adds execute permission only for the owner (user) on all .sh files in scripts/. chmod +x or a+x adds execute for all users. chmod og+x adds execute for group and others only.

🧠 Conceptual

expert

What is the effect of chmod 4755 script.sh?

You run chmod 4755 script.sh on a script. What does the '4' in the permission number do?

A It sets the setuid bit, causing the script to run with the file owner's permissions.

B It sets the read permission for the owner only.

C It sets the execute permission for group and others only.

D It sets the sticky bit, preventing others from deleting the file.

💡 Hint

The first digit in chmod numeric mode sets special permissions like setuid, setgid, and sticky bit.

The leading '4' sets the setuid bit. This means when the script runs, it runs with the permissions of the file owner, not the user who runs it. This is often used for programs needing elevated privileges.

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