I saw a post internally that asked this question: Anyone have a handy powershell script testing if the installed flyway version matches a specific string?
That seemed simple, but getting program output from PoSh wasn’t something I’ve tried. So I tackled the challenge and this is what happened.
Getting the Output
The first thing I wanted to do was actually figure out what the output of checking the version was from the CLI. I looked at the help and noticed a version verb. When I run that, I see a bunch of lines of output.
A lot of output. I need to parse a bunch of strings, and then find a line.
My first experiment was to run this to get a file with this output.
flyway version > fwversion.txt
Now, let’s parse this.
Parsing Content
It’s been awhile since I read stuff from a file, but I know Get-Content works to read the file. What about finding a line. I saw this post with an answer that noted Select-String can be used, so I decided to try that.
Here’s a first cut of code:
That didn’t work. However, with some experiments, I tried this code:
Get-content fwversion.txt | select-string 'Edition'
That worked.
Now, I’ll assign that to a variable with this code:
$a=Get-content fwversion.txt | select-string ‘Edition’
Next, I’ll split this string by spaces into a new variable with this:
$b = $a -split(‘ ‘)
Then I can evaluate the various element of $b. You can see below the first and third elements are what I’m interested in. Really the third. Remember, PoSh is zero-based.
That let’s me parse the output, but I don’t want to save a file. Now on to the next step.
Capturing the Output from a Program
One of the things I know you can do in a PoSh ptompt is run a program. The redirection operator allows you to move output. When I tried it, I couldn’t quite get the output I wanted, but I did find this post that helped. With that, I ran this code:
$a = & "flyway" --version 2>&1 | select-string 'Edition'
This runs Flyway, captures the output in a stream and then uses the code above to find the right line. I assign this to a variable.
Almost there.
Adding a Parameter and a Test
Since I want to call this from the CLI and pass i a parameter, I added a param() clause to my script and then a test that compares the version output from the flyway.exe to the parameter. That gest me this code:
param(
[string]$versionToCheck=""
)
$a = & "flyway" --version 2>&1 | select-string 'Edition'
$b = $a -split(' ')
if ($b[3] -eq $versionToCheck)
{ Write-Output("$($b) installed")}
else {
Write-Output(“wrong version – $($b) installed”)
}
Now I can call this from the CLI and check things. It works well. At least for now.
I am certainly not a PoSh expert, but this short script took me about 15 minutes to write with a little research. Then a little testing and I sent it off to the requester. Haven’t heard any complaints, so I’m hoping this actually works for them.
Voice of the DBA 