Replace text between two lines with contents of a file stored in a variable in sed

Question

Let's say I have a file called original.txt with this content:

red
blue
water
food
tree
gray
white

Also I have a file called new.txt with this content:

green
black
yellow
purple

Now I want to write a script that replaces the lines between blue and gray in original.txt with the contents of new.txt, so it gives me this result:

red
blue
green
black
yellow
purple
gray
white

I wrote this piece of code for the purpose (the name of the new file is not always the same so it's stored in a variable):

newtext="new.txt"

sed -i "/blue/,/gray/{
    r $newtext
    d
}" original.txt

However, when running it I get this nonsense instead:

red
green
black
yellow
purplegreen
black
yellow
purplegreen
black
yellow
purplegreen
black
yellow
purplegreen
black
yellow
purplewhite

What am I doing wrong?

Answer 1

This might work for you (GNU sed):

sed '/blue/,/gray/!b;//!d;/blue/r file2' file1

For the range of lines between blue and gray, delete lines that do not match either the first or the last lines in the range and read the lines to insert before the last line of the range.

EDIT:

The first sed command /blue/,/grey/!bmatches a range of lines i.e. the lines that range between a line containing blue upto and including a line containing gray. The !b part means if the lines are not in that range then break out of the sed commands i.e. do not do any further sed processing for these lines, just print as normal.

The sed commands following will only affect those lines that are in the range between blue and gray.

The second command //!d means: delete those lines that do not match either the start/end of the range i.e. blue or gray. The // uses the regexp from a previous /.../ command. N.B. a delete command terminates any further sed processing for that line.

The sed commands following will only affect lines that containing either blue or gray.

The third command matches a line containing blue and reads in lines from file2.

N.B. the lines containing blue and grey are processed by sed naturally and printed before the next line is read into the pattern space as are the lines not between blue and gray.

An alternative:

sed '/blue/,/gray/!b;//!d;/gray/e cat file2' file1

And another:

sed -ne '/blue/{p;r file2' -e ':a;n;/gray/!ba};p' file1

Answer 2

sed is for s/old/new/, that is all. For anything else you should be using awk:

$ awk 'NR==FNR{new = new $0 ORS; next} /gray/{f=0} !f{print} /blue/{printf "%s",new; f=1}' new.txt original.txt
red
blue
green
black
yellow
purple
gray
white

The above will work in any awk in any shell on any UNIX box and does not require any of the start/end regexps to be repeated. Very importantly it can also trivially be built upon to do anything else you want now or in future! For example to be able to specify the beginning and ending regexps as arguments would be:

$ awk -v beg='blue' -v end='gray' 'NR==FNR{new = new $0 ORS; next} $0~end{f=0} !f{print} $0~beg{printf "%s",new; f=1}' new.txt original.txt

ad then you can change them:

$ awk -v beg='water' -v end='tree' 'NR==FNR{new = new $0 ORS; next} $0~end{f=0} !f{print} $0~beg{printf "%s",new; f=1}' new.txt original.txt
red
blue
water
green
black
yellow
purple
tree
gray
white

Anything you might want to do is just a simple rearrangement using the same constructs, e.g. to not print the beginning line:

$ awk -v beg='blue' -v end='gray' 'NR==FNR{new = new $0 ORS; next} $0~end{f=0} $0~beg{printf "%s",new; f=1} !f{print}' new.txt original.txt
red
green
black
yellow
purple
gray
white

and similar tweaks to not print the ending line or not print both or do anything else....