what exactly are you trying to achieve with

perl -ne 'print;' *.txt > all.csv
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or

for file in *.txt; do   cat "$file";   echo; done > newfile.csv
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??? Those are a bit pointless, just concatenating files into another file, same as just doing

cat *.txt > newfile.txt
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And these are not magically creating csv format for you - it's just the same text as in the input files. No idea what you mean with "how to import it to db perl -MCPAN -e shell"???