Linux: How to replace all text between two lines and substitute it with the output of a variable using sed?

Question

I have a problem that is very similar to this SO thread: how to replace all lines between two points and subtitute it with some text in sed

Consider a problem like this:

$ cat file
BEGIN
hello
world
how
are
you
END

$ sed -e '/BEGIN/,/END/c\BEGIN\nfine, thanks\nEND' file
BEGIN
fine, thanks
END

How might I inject text that I have saved to a variable like:

str1=$(echo "This is a test")

How can I inject str1's output in the place of fine, thanks , like:

sed -e '/BEGIN/,/END/c\BEGIN\n$str1\nEND' file  # fails to work as hoped

I also want to save the output to overwrite the file.

Answer 1

Sure is easy in awk .

Given:

cat file
ABC
BEGIN
hello
world
how
are
you
END
XYZ

You can do:

str='TEST'

awk -v r="$str" -v f=1 '/^BEGIN$/{print $0 "\n" r; f=0}
/^END$/{f=1} f' file

Prints:

ABC
BEGIN
TEST
END
XYZ

---

If you want to embed another file in between those marks:

awk -v f=1 -v fn='ur_file' '/^BEGIN$/{
    print $0
    while ((getline<fn)>0) {print}
    f=0}
/^END$/{f=1} f' file

Answer 2

You can probably use this sed :

sed -e '/BEGIN/,/END/ {//!d; /BEGIN/r file.html' -e '}' file

This will insert content of file.html file between BEGIN and END . To save changes back to file:

sed -i -e '/BEGIN/,/END/ {//!d; /BEGIN/r file.html' -e '}' file