Can anyone share an example of how to unzip/decompress a file in a workflow?

I saw this question and attempted to test the same but unfortunately couldn't get it to work with either a zip or gz. my js ended up looking like:

var cmdStr="unzip -j /folder/folder/folder/tester.zip -d folder/folder/folder";

var res=execCommand(cmdStr);

i also read elsewhere that decompressing a file is possible in the data loading activity, by choosing 'pre-process the file' then inputting gunzip -c <%= vars.sourceFile %>

again couldn't get this to work

lastly i tried gunzip in a js activity, code was like:

execCommand('cd /folder/folder/folder \n gunzip "tester.csv.gz" ');

but again couldn't get it to work. am sure i am doing something basic wrong but error message just says error while evaluating so not sure what.