Editing Integration of CodeRunner with MAMP (section)

== Why <code>$filename</code> uses that odd quoting pattern ==

CodeRunner handles <code>$filename</code> by directly replacing the text <code>$filename</code> in the Run Command field with the actual file path string — it's not spawning a shell first and passing in a variable. In other words, CodeRunner does '''text substitution''', not shell variable expansion.

Since the whole command is wrapped in single quotes <code>'...'</code> for <code>sh -c</code>, the shell won't expand anything inside those single quotes at all. If <code>$filename</code> were left inside the single quotes, it would be treated as the '''literal text''' <code>$filename</code>, not the actual path CodeRunner substitutes in.

The fix is to "step out" of the single-quoted string right where <code>$filename</code> needs to go, let CodeRunner substitute it outside the quotes, then step back into the single-quoted string:

<pre>
"'"$filename"'"
</pre>

Broken down:

<pre>
"'   →  closing double quote + closing single quote (temporarily exits the string)
"$filename"  →  outside the single quotes, so CodeRunner replaces it with the actual file path
'"   →  opening single quote + opening double quote (re-enters the string)
</pre>

This is a common shell trick: '''inserting content that needs to be expanded in the middle of a single-quoted string'''. Since single quotes never expand anything inside them, the only way to splice in something that needs expanding is to end the single-quoted string, insert the piece, then start a new single-quoted string right after.