Saturday, 25 February 2017

It's the end of the line

When working on an install script recently, I came across one of those bugs that make you realise just how pedantic computer programming can be. I had a file that contains a list of yum package names and a script that read the file and did some work on them.



while read PKG; do
    yum install -y ${PKG}
done < /path/to/PackageList.txt

This file had been working fine as part of our installer for a number of iterations. As part of a developing a new feature I added a new package to the list and saved the file. Thinking this was such a small change that it would just work, I committed it and pushed the changes. However when running the script our tester complained that the new package was missing.

I sat down to debug the issue by checked that the package existed, that the script hadn't changed, and that I had the package name correct. As part of this debugging I resaved the file and it worked again.

After scratching my head, getting a cup of tea and doing some searching, I discovered that the posix standard specifies that a newline character should be added to the end of files. My editor of choice for development is Sublime Text, which by default doesn't add the newline character to the end of the file.

In order to turn it on you should edit your preferences to change the following preference to true.

// Set to true to ensure the last line of the file ends in a 
// newline character when saving
"ensure_newline_at_eof_on_save": true

You may also see the symptom of this issue when committing files to source control and at the end of a diff you will see.

\ No newline at end of file

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