How can awk search a string without using regular expression?

Shell Programming and Scripting
1

Hello,
Awk seem treat the pattern as regular expression, how can awk search not using regular expression? e.g. [Aa] just represent for "[Aa]", not "A" or "a" . I don't want to add backslash [ and ] .

2

You need to treat the pattern as a literal string.

3 
printf "he[ll]o\nhi\n" | awk 'index($0, "[ll]")'
he[ll]o