🚀 Bash: Running Scripts – Using bash script.sh and ./script.sh Explained

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🧲 Introduction to Running Bash Scripts – Execute with bash or ./

Once a Bash script is written, you need to execute it. There are two primary ways to run a Bash script:

• Using the bash command (explicit interpreter)
• Using ./script.sh (execute permission + shebang)

Each method has different implications on permissions, execution environment, and portability. Understanding them helps ensure your scripts run reliably across systems.

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🎯 In this article, you’ll learn:

• How to execute scripts using bash script.sh and ./script.sh
• The difference between interpreting vs executing directly
• Why execution permissions and shebang matter
• Best practices for safe and consistent script execution

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🧪 Method 1: Run with bash script.sh

This method explicitly calls the Bash interpreter:

bash myscript.sh

✅ Use this when:

• The script is not executable
• You want to override the shebang interpreter
• You’re testing with different shell versions

🔎 This method ignores the shebang (#!/bin/bash) line and uses the specified interpreter (bash) directly.

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🧪 Method 2: Run with ./script.sh

This method requires the script to be executable and relies on the shebang line.

Steps:

chmod +x script.sh     # Make script executable
./script.sh            # Execute script directly

✅ Use this when:

• You want the OS to auto-detect the interpreter from the shebang
• The script should be portable and standalone
• You’re scheduling it in cron or calling from another program

💡 If the script lacks a valid shebang, it may fail or be run by the wrong shell (/bin/sh).

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⚠️ Common Errors and Fixes

Error	Cause	Fix
Permission denied	Script not executable	chmod +x script.sh
command not found: script.sh	Not using ./ for local scripts	Use ./script.sh or full path
bad interpreter: No such file	Invalid or missing shebang	Use #!/bin/bash as first line
Script not using Bash syntax	System default is /bin/sh	Run with bash script.sh or add shebang

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📁 Example Script

#!/bin/bash
echo "Hello from Bash script!"

Save this as hello.sh, then:

chmod +x hello.sh
./hello.sh

✅ Output:

Hello from Bash script!

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🧠 Summary of Execution Differences

Method	Uses Shebang?	Needs Execute Permission	Notes
bash script.sh	❌ No	❌ No	Always runs under bash
./script.sh	✅ Yes	✅ Yes	Honors the shebang interpreter

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📌 Summary – Running Bash Scripts

You can run Bash scripts using either bash script.sh (interpreter-first) or ./script.sh (shebang-based execution). Knowing when to use each method helps you create robust and portable scripts for real-world tasks.

🔍 Key Takeaways:

• bash script.sh ignores shebang and doesn’t require execute permission
• ./script.sh requires chmod +x and a valid shebang
• Use ./ for production scripts with portability
• Use bash for testing or interpreter-specific runs

⚙️ Real-world Uses:

• Deploying system automation via executable scripts
• Running scripts from cron or CI/CD pipelines
• Debugging with specific shell interpreters

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❓ FAQ – Running Bash Scripts

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❓ Do I need #!/bin/bash in every script?
✅ Yes, if you use ./script.sh, it tells the system which interpreter to use.

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❓ Why does ./script.sh give ‘permission denied’?
✅ You haven’t made it executable. Run:

chmod +x script.sh

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❓ Is bash script.sh better than ./script.sh?
✅ It depends. bash script.sh is great for manual testing, while ./script.sh is preferred for production usage and portability.

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❓ Can I run a script without shebang?
✅ Yes, but only with bash script.sh. ./script.sh requires a valid shebang to work correctly.

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❓ How do I run a script from any directory?
✅ Place it in a directory listed in $PATH, or call it with full path:

/path/to/script.sh

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