Shell script to append text to each file?

sed -i.bak "$ a $(<file_block_of_text)" *.txt

Use append redirection.

for f in *.txt
do
  cat footer >> "$f"
done

If you're needing to do this via a script, you can use echo and append redirection to get the extra text into the files.

FILES=pathto/*
for f in $FILES ; do
    echo "#extra text" >> $f
done

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