For a long time, I’ve been naming my shell scripts with the <code>.sh</code> extension and assuming they’d run just fine in any shell. Most of the time, they worked perfectly—but every now and then, I’d hit unexpected issues, especially when running them with <code>sh scriptName.sh</code>.This got me thinking: Why do we even name our scripts <code>scriptName.sh</code>? Shouldn't it be <code>scriptName.bash</code> if it's written specifically for Bash?<figure class="image"><img src="https://images.unsplash.com/photo-1475079385159-08c8fd87a2ed?crop=entropy&amp;cs=tinysrgb&amp;fit=max&amp;fm=jpg&amp;ixid=M3wxNTQwMTB8MHwxfHNlYXJjaHw5MHx8c2hlbGx8ZW58MHx8fHwxNzMyODA0NTIyfDA&amp;ixlib=rb-4.0.3&amp;q=80&amp;w=1080"><figcaption>Photo by <a target="_blank" rel="noopener noreferrer" href="https://unsplash.com/@lauren_abrahall?utm_source=DNX&amp;utm_medium=referral">Lauren</a> on <a target="_blank" rel="noopener noreferrer" href="https://unsplash.com/?utm_source=DNX&amp;utm_medium=referral">Unsplash</a></figcaption></figure><h3>The Shebang Problem</h3>Most of my scripts begin with a shebang like this:<pre><code class="language-css">#!/bin/bash</code></pre>This line ensures the script is executed with Bash when run directly, for example:<pre><code class="language-css">./scriptName.sh</code></pre>However, if I run the same script with:<pre><code class="language-css">sh scriptName.sh</code></pre>The shebang is completely ignored! Instead, the script is executed using <code>sh</code> (which might point to a more basic shell like <code>dash</code> on many systems). This often works fine—until the script relies on Bash-specific features.<h3>What Happens When <code>sh</code> Runs a Bash Script?</h3>Here’s an example of a script that breaks when run with <code>sh</code>:<pre><code class="language-css">#!/bin/bash
echo "Using Bash!"
my_array=(one two three)
echo "Second element: ${my_array[1]}"</code></pre>Run with Bash (or Directly):<pre><code class="language-css">./scriptName.sh</code></pre>Output:<pre><code class="language-css">Using Bash!
Second element: two</code></pre>Run with <code>sh</code>:<pre><code class="language-css">sh scriptName.sh</code></pre>Output:<pre><code class="language-css">Using Bash!
scriptName.sh: 3: scriptName.sh: Syntax error: "(" unexpected</code></pre>The error occurs because <code>sh</code> doesn’t support arrays or other Bash-specific features. This happens because the <code>sh</code> command forces the use of a simpler shell, completely ignoring the shebang.<h3>Why <code>.sh</code> Can Be Misleading</h3>Naming a script <code>scriptName.sh</code> implies it’s compatible with <code>sh</code> (or any POSIX-compliant shell). But if your script relies on Bash-specific features, this isn’t true. This mislabeling can confuse others—or even you—into running the script incorrectly.<h3>A Case for <code>.bash</code></h3>If a script depends on Bash, naming it with the <code>.bash</code> extension might be more accurate. For example:<pre><code class="language-css">scriptName.bash</code></pre>This naming convention immediately signals that the script is Bash-specific, reducing the likelihood of running it with <code>sh</code> by mistake.<h3>What I’ve Learned (and What I’ll Do Differently)</h3><ol><li>Be Explicit with the Interpreter:</li></ol>If my script starts with <code>#!/bin/bash</code>, I’ll always run it using Bash:<pre><code class="language-css">bash scriptName.sh</code></pre><ul><li>If a script is POSIX-compliant, I’ll test it with <code>sh</code> to ensure compatibility.</li></ul><ol><li>Use the Shebang Correctly:</li></ol>Make scripts executable and run them directly:<pre><code class="language-css">chmod +x scriptName.sh
./scriptName.sh</code></pre><ol><li>Adopt Clear File Extensions:<ul><li>Use <code>.sh</code> only for POSIX-compliant scripts.</li><li>Use <code>.bash</code> for scripts that rely on Bash-specific features.</li></ul></li><li>Write Scripts with Compatibility in Mind:<ul><li>If I expect the script to be run with <code>sh</code>, I’ll avoid Bash-only features like arrays or <code>[[ ]]</code>.</li><li>If it’s written for Bash, I’ll clearly document it and name it appropriately.</li></ul></li></ol><h3>Moving Forward</h3>Understanding the difference between <code>sh</code> and <code>bash</code> and how the shebang works has saved me a lot of frustration. Going forward, I’ll pay closer attention to how I name and run my scripts to ensure compatibility and clarity.What about you? Have you ever run into similar issues with <code>.sh</code> scripts or interpreter mismatches? Let me know your thoughts—I’d love to hear your experiences!

For a long time, I’ve been naming my shell scripts with the .sh extension and assuming they’d run just fine in any shell. Most of the time, they worked perfectly—but every now and then, I’d hit unexpected issues, especially when running them with sh scriptName.sh.

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