# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/(\w)(nin)\b/$1NG/g;t' <<< "yilanin
suyunin
kalinin
batinin
kinindan
sininteki
nin
ninkisi
xxxnin
xxxninxxx
nin"
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for SED, please visit: https://www.gnu.org/software/sed/manual/html_node/The-_0022s_0022-Command.html