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.