sed and awk: how to replace a section of file to another content?

Question

File a.html:

<!--TEMPLATE: banner-->
blahblah
<!--TEMPLATE-END: banner-->

I want to replace the middle text to some other text, how to achieve that using sed/awk/other tools?

Answer 1

If the text between the marker lines consists of one or more lines:

sed '/<!--TEMPLATE: banner-->/,/<!--TEMPLATE-END: banner-->/ {//!d}; /<!--TEMPLATE: banner-->/aSome text to insert' a.html

The i command could be changed to an r command and a file name to read the text from a file.

sed '/<!--TEMPLATE: banner-->/,/<!--TEMPLATE-END: banner-->/ {//!d}; /<!--TEMPLATE: banner-->/r filename' a.html

Answer 2

If you have the new banner text in another file:

awk -v new_file=new_banner.txt '
    /!--TEMPLATE:/ {print; system("cat " new_file); banner=1; next}
    /!--TEMPLATE-END:/ {banner=0}
    banner {next}
    {print}
' a.html