Software development is a neverending string of “What happens if I…?” Each new runtime, language, or tool is a new world with its own laws of nature. We get to explore each one with experiments.
Objective
Today I added another alias to my PowerShell $profile:
echo "Good morning!"
# ...
Function ListFilesWithMostRecentAtBottom {
Get-ChildItem | Sort-Object -Property LastWriteTime
}
Set-Alias ll ListFilesWithMostRecentAtBottom
To use that alias in my current shell, I need to source the profile again. I googled how to do this. The first useful page said:
& $profile
So I typed that. It echoed “Good morning!” but the alias did not work.
Hmm, did it not save?
I can test that. I changed the echo to “Good morning yo!” and tried again.
It printed the new text, but still didn’t get the alias.
Hmm, is something wrong with the alias?
I opened a new shell window to test it.
The new alias works in the new window. Therefore, it’s the & $profile command that is not doing what I want.
Investigation
I could ignore the problem and continue work in the new window. My alias is working there. But dang it, I want to understand this. I want to know how to reload my $profile in the future.
Time for more googling. The next post had a new suggestion:
. $profile
I typed that, and it worked. yay!
But wait, was that the old window or the new window? What if it only worked becuase I was in the new window?
I want to be certain that running . $profile brings in any new aliases I just added. For a proper experiment, I need to see the difference.
Experiment
I add a new alias to my $profile, and also change the echo so that I’ll be sure it’s running the new version.
echo "Good morning yo tyler!"
# ...
Function ListFilesWithMostRecentAtBottom {
Get-ChildItem | Sort-Object -Property LastWriteTime
}
Set-Alias ll ListFilesWithMostRecentAtBottom
Set-Alias tyler ListFilesWithMostRecentAtBottom
In my terminal, I run tyler as a test case, then the command I’m investigating (. $profile), then the test case tyler again.
Now I can see the before and after, and they’re different. I can tell that . $profile has the desired effect. Now I have learned something about PowerShell.
Epilogue
I remove the extra tyler stuff from $profile.
As far as I can tell, & runs the script in a subshell, and . runs the contents of the script in the current shell. The . command works like this in bash too, so it’s easy for me to remember.
Today I took a few extra minutes and several extra steps to make an experiment and figure out what PowerShell was doing. Now I know how to reload my $profile. Now you know how to run a tiny experiment to ascertain that what just happened, happened for the reason you think it did.