I have a mini-system with only limited number of binaries (bash,cp,cat,sed, ...). I don't have tail command, and I am wondering if I could emulate tail functionality with sed
cat foo.txt | tail -n 10 I know that I can print lines 1-10 with sed cat foo.txt | sed -n '1,10p', but how would I print the last 10 lines?
You could do something like this:
sed -e :a -e '$q;N;11,$D;ba' 
sed -e :a -e '$q;N;11,$D;ba' foo to match the question. sed -e '1,11p' -e :a -e '$q;N;11,$D;ba' But I'd still like to understand the tail part !!! sed -e :a -e '$q;N;11,$D;ba' in .bashrc? When I tried alias tsed="sed -e :a -e \'$q;N;4,$D;ba\'" it gives me: sed: -e expression #2, char 1: unknown command: `'' N: command not found 11,: command not found tac foo | sed -n '1,10p' | tac but if you don't have tac, you can use only sed this way :
sed -n '1!G;h;$p' foo | sed -n '1,10p' | sed -n '1!G;h;$p' Is expr available with your system? Then you can try evaluating the desired line number after you have counted the total number of lines in the file.
I created a file named tmp containing the numbers from 1 to 20 in each line.
nlines=$(cat tmp | sed -n '$=') cat tmp | sed -n $(expr $nlines - 9),"$nlines"p 11 12 13 14 15 16 17 18 19 20 Of course, you can use wc -l, if available.
The command to compute the total number of lines in the file is taken from sed one liners. However, I haven't checked if it works with empty files too.
P.S. If expr is not available, you can use subtract numbers in Bash as shown below:
cat tmp | sed -n $((nlines-9)),"$nlines"p 
