man touch…
… is the silly thing i’ve typed into my terminal today. Why? As a result of business needs, one of the common tasks in my office is to copy data between cloud storage buckets across multiple accounts.
Recently, our devops team found a bug in our copy scripts that copied files into
directories named after themselves. So, for example a file at
~/Documents/my_doc.md that is to be copied to the root of a bucket would be
copied to /Documents/my_doc.md/my_doc.md.
I wanted to recreate this issue locally using tools that i’m familiar with. I wanted to try to create a file when the directory exists where both the file and directory have the same name:
> mkdir deleteme.md
> touch deleteme.md
If you try to do this, the directory deleteme.md gets created but no file is
created. I was expecting that touch deleteme.md would produce an error but it
did not.
Conversely, creating the file first and then the directory, results in an error:
> touch deleteme.csv
> mkdir deleteme.csv
mkdir: deleteme.csv: File exists
At this point, I’m confused. Why doesn’t touch fail the first time around?
I’ve been consistently taught to use touch to create files. That advice seems
misguided though if touch doesn’t give an error when a file isn’t created when
the command is given to create the file.
I bring this to one of my coworkers and he has one piece of advice:
man touch
Although the specific language changes by the specifics of the machine, the
purpose of touch is to change access and modification times of files.
Creating files happens as a side-effect of touch.
At the end of the day, I think that all of this is fine and I’ve learned a lot. I learned that tools I commonly use may not have the purpose I expect. I learned that it’s important to consult the manual. And I learned that sometimes with shell scripting, we use tools in a certain way because we figured that the tool works just fine.