However, it prints out each lines twice, which is in the same order as in the file. What am I doing wrong?

The -p switch implies print. See perlrun.

Invoking perl with -p and an empty script body does the trick: 

perl -pe '' dataoutput.txt

[download]

In your second example, you are just printing a newline character before the implicit print is done, hence the empty lines.

perl -le'print map{pack c,($-++?1:13)+ord}split//,ESEL'

In reply to Re: oneliner cat like capability by shmem
in thread oneliner cat like capability by gradius85

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