As far as I can tell, perl really ought to treat the "command" as a string and not attempt to compile it.

Did you expect it to leave $un and $jpeg untranslated as well? Or did you expect perl to parse it and replace it with the contents of those variables?

I suspect something similar it going on here. for some reason it is checking Byte (or maybe its the @{...}) as a replaceable part and then finds [] which it doesnt like.

i would do something like this.

my $command='Set-ADUser '.$un.' -Replace @{thumbnailPhoto=([Byte[]](Ge
+t-Content '.$jpeg.' -Encoding Byte))}'; 
my $result = `c:\\windows\\system32\\windowspowershell\\v1.0\\powershe
+ll.exe -command "$command"`;
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