sed '/blue/,/gray/!b;//!d;/blue/r file2' file1For 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 file2=2.txtsed -i "/green/,/gray/!b;//!d;/green/r $file2" 1.txt file2=2.txtsed -i "/green/,/gray/!b;//!d;/gray/e cat $file2" 1.txt