unix - head AND tail of file

Question

Say you have a txt file, what is the command to view the top 10 lines and bottom 10 lines of file simultaneously?

i.e. if the file is 200 lines long, then view lines

Answer 1

For a pure stream (e.g. output from a command), you can use 'tee' to fork the stream and send one stream to head and one to tail. This requires using either the '>( list )' feature of bash (+ /dev/fd/N):

( COMMAND | tee /dev/fd/3 | head ) 3> >( tail )

or using /dev/fd/N (or /dev/stderr) plus subshells with complicated redirection:

( ( seq 1 100 | tee /dev/fd/2 | head 1>&3 ) 2>&1 | tail ) 3>&1
( ( seq 1 100 | tee /dev/stderr | head 1>&3 ) 2>&1 | tail ) 3>&1

(Neither of these will work in csh or tcsh.)

For something with a little better control, you can use this perl command:

COMMAND | perl -e 'my $size = 10; my @buf = (); while (<>) { print if $. <= $size; push(@buf, $_); if ( @buf > $size ) { shift(@buf); } } print "------\n"; print @buf;'