I am fairly new to powershell coding and fiddled around a bit, after learning some basics in here.
I wanted to store the success message in a variable after running following command:
docker cp <dockerid>:path/file localpath/file
It returns:
Successfully copied 13.8kB to localpathfile
Thats what i did in a script:
$return = docker cp <dockerid>:path/file localpath/file
The file gets copied, but the variable $return is empty afterwards.
What i dont understand is, i used something similar already:
$dockerID = docker ps -a -q --filter name=^/$containername$
and that one does work and $dockerID is filled afterwards.
Does anybody know the reason?
3
The reason $return is empty is likely because your command did not exit properly with code 0, and therefore, did not return the stdout stream. This suggests that, despite the file being copied, an error occurred causing the command to exit with code 1, returning the stderr stream instead.
The PowerShell variable will only populate if the command successfully returns stdout.
If you really want to populate the variable (despite the command giving error), you would need to redirect the stderr stream to stdout stream by using 2>&1:
$return = docker cp <dockerid>:path/file localpath/file 2>&1
However, this may not be good advice if you’re new to PowerShell, as it’s important to learn how to handle errors when calling external commands. For example, you can use $LASTEXITCODE to check the exit status.
$return = docker cp <dockerid>:path/file localpath/file
if ($LASTEXITCODE -ne 0) {
throw "The 'docker cp' command had errors"
}
If your command exits successfully with code 0 and returns stdout, then $return will be populated. Otherwise, if an error occurs, the if statement will catch it, and throw will trigger a terminating error, stopping the script’s execution.