# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/\b[uU](?=\b|(?![^\W\d_]))\.?\s*/utca /gm;t' <<< "Holics u 5/a\",
\"Holics U 5/a\",
\"Holics u5/a\",
\"Huolics u 5/a\",
\"Holics u. 5/a\",
\"Holuics u5\",
\"Holics and other stuff u more stuff after 5\",
\"Houlics utca 5"
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