I'm not sure what you are asking for. Writing out a script from Perl is just like writing any other text file, except for things like execute access.
The code you give:

#!/bin/sh # df -k /var/log # end of script
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will not work - unlike Perl, shells take a newline (or a ;) as a statement terminator - that line will be seen as one #! line:

#!/bin/sh 
# df -k /var/log 
# end of script
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is just three lines of comments, so you should loose the second #.
Ever considered using Perl instead of the shell?