# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/<a\s[^>]*?href\s*=\s*\\'https?:\/\/site\.ru\/[^>]+>\s*<img.+?<\/a>//gs;t' <<< "<a class=\'fancybox\' href=\'http://site.ru/upload/manuals/3V/image_2022_01_28T12_03_17_757Z.jpg\' rel=\'group\'><img src=\'http://site.ru/upload/manuals/3V/image_2022_01_28T12_03_17_757Z.jpg\' width=\'400px\'></img></a>
<a class=\'fancybox\' href=\'http://site2.ru/upload/manuals/3V/image_2022_01_28T12_03_17_757Z.jpg\' rel=\'group\'><img src=\'http://site2.ru/upload/manuals/3V/image_2022_01_28T12_03_17_757Z.jpg\' width=\'400px\'></img></a>
<a class=\'fancybox\' href=\'http://site.ru/upload/manuals/3V/image_2022_01_28T12_03_17_757Z.jpg\' rel=\'group\'><img src=\'http://site.ru/upload/manuals/3V/image_2022_01_28T12_03_17_757Z.jpg\' width=\'400px\'></img></a>"
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