Anchor(faq19)

How can I split a file into line ranges, e.g. lines 1-10, 11-20, 21-30?

Some Unix systems provide the split utility for this purpose: 

    split --lines 10 --numeric-suffixes input.txt output-

For more flexibility you can use sed. The sed command can print e.g. the line number range 1-10: 

    sed -n '1,10p'

This stops sed from printing each line (-n). Instead it only processes the lines in the range 1-10 ("1,10"), and prints them ("p"). sed still reads the input until the end, although we are only interested in lines 1 though 10. We can speed this up by making sed terminate immediately after printing line 10: 

    sed -n -e '1,10p' -e '10q'

Now the command will quit after reading line 10 ("10q"). The -e arguments indicate a script (instead of a file name). The same can be written a little shorter: 

    sed -n '1,10p;10q'

We can now use this to print an arbitrary range of a file (specified by line number): 

file=/etc/passwd
range=10
firstline=1
maxlines=$(wc -l < "$file") # count number of lines
while (($firstline < $maxlines))
do
    ((lastline=$firstline+$range+1))
    sed -n -e "$firstline,${lastline}p" -e "${lastline}q" "$file"
    ((firstline=$firstline+$range+1))
done

This example uses ["BASH"] and KornShell ArithmeticExpressions, which older [wiki:BourneShell Bourne shells] do not have. In that case the following example should be used instead: 

file=/etc/passwd
range=10
firstline=1
maxlines=`wc -l < "$file"` # count line numbers
while [ $firstline -le $maxlines ]
do
    lastline=`expr $firstline + $range + 1`
    sed -n -e "$firstline,${lastline}p" -e "${lastline}q" "$file"
    firstline=`expr $lastline + 1`
done