The error message "awk: warning: escape sequence '<' treated as plain '>'" typically occurs when you are using the awk command and you have included a < character in the search pattern or replacement string, but you have not properly escaped it.
In awk, the < and > characters have special meaning as comparison operators. To treat them as plain characters, you need to escape them using a backslash (\).
Here's an example of how you might use the awk command to search for a string containing a < character and replace it with another string:
awk '{ gsub("<", "<"); print }' input.txt > output.txt
In this example, the gsub function is used to search for the < character in the input file input.txt and replace it with the string <. The < sequence is the HTML entity for the < character, and it will be treated as a plain string by awk.
If you don't properly escape the < character, awk will treat it as a comparison operator and you will see the warning message "awk: warning: escape sequence '<' treated as plain '>'".
To avoid this error, make sure to properly escape any special characters in your search patterns or replacement strings when using the awk command.