# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/(?<=<\\/a>)(\w+)/ $1/gm;t' <<< "<a href=\"blah.com\">Hello</a>World // Here we need to put space between Hello and World
<a href=\"blah.com\">Hello</a> World // Do not touch this
<a href=\"blah.com\">Hello</a><b>World</b> // do not touch this"
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