How to delete all the lines after the last occurence of pattern?

Question

i want to delete all the lines after the last occurence of pattern except the pattern itself

file.txt

honor
apple
redmi
nokia
apple
samsung
lg
htc

file.txt what i want

honor
apple
redmi
nokia
apple

what i have tried

sed -i '/apple/q' file.txt

this deletes all the line after the first occurence of pattern -

honor

Answer 1

Simple, robust 2-pass approach using almost no memory:

$ awk 'NR==FNR{if (/apple/) hit=NR; next} {print} FNR==hit{exit}' file file
honor
apple
redmi
nokia
apple

If that doesn't execute fast enough THEN it's time to try some alternatives to see if any produce a performance improvement.

Answer 2

Reverse the file, print everything starting from the first occurrence of the pattern, then reverse the result:

tac file.txt | sed -n '/apple/,$p' | tac > newfile.txt

You can find the line number of the last match, then use that to print the first N lines of the file:

line=$(awk '/apple/ { line=NR } END {print line}')
head -n $line file.txt > newfile.txt

Answer 3

If you don't want to reverse the file as Barmar suggests, you will either have to read the file in reverse using lower level tools (eg, fseek) or read it twice:

sed $(awk '/apple/{a=NR}END{print a+1}' input),\$d input

(Note that if the pattern does not appear in the file, this will output nothing. That's an edge case you should worry about.)