Use sed with ignore case while adding text before some pattern

Question

sed -i \'/first/i This line to be added\' 

In this case,how to ignore case while searching for pattern =first

Answer 1

For versions of awk that don't understand the IGNORECASE special variable, you can use something like this:

awk 'toupper($0) ~ /PATTERN/ { print "string to insert" } 1' file

Convert each line to uppercase before testing whether it matches the pattern and if it does, print the string. 1 is the shortest true condition, so awk does the default thing: { print }.

To use a variable, you could go with this:

awk -v var="$foo" 'BEGIN { pattern = toupper(foo) } toupper($0) ~ pattern { print "string to insert" } 1' file

This passes the shell variable $foo and transforms it to uppercase before the file is processed.

Slightly shorter with bash would be to use -v pattern="${foo^^}" and skip the BEGIN block.