if you are not familiar with sed, then you can use here document as alternative to help you write some text without open a text editor like vim, nano, etc.
bash
tee /path/to/dir/filename.txt << "EOF"
hemlo
EOF
you can use cat, but with tee, you have an advantage of saving a file as root using sudo.
bash
cat >/path/to/dir/filename.txt << "EOF"
hemlo
EOF
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