Move top 1000 lines from text file to a new file using Unix shell commands

Question

I wish to copy the top 1000 lines in a text file containing more than 50 million entries  to another new file  and also delete these lines from the original file   Is there some way to do the same with a single shell command in Unix

User · Answer

Out of curiosity  I found a box with a GNU version of sed  v4 1 5  and tested the  uncached  performance of two approaches suggested so far  using an 11M line text file     wc -l input 11771722 input    time head -1000 input  gt  output  time tail -n  1000 input  gt  input tmp  time cp input tmp input  time rm input tmp  real    0m1 165s user    0m0 030s sys     0m1 130s  real    0m1 256s user    0m0 062s sys     0m1 162s  real    0m4 433s user    0m0 033s sys     0m1 282s  real    0m6 897s user    0m0 000s sys     0m0 159s    time head -1000 input  gt  output  amp  amp  time sed -i  1  999d  input  real    0m0 121s user    0m0 000s sys     0m0 121s  real    0m26 944s user    0m0 227s sys     0m26 624s   This is the Linux I was working with     uname -a Linux hostname 2 6 18-128 1 1 el5  1 SMP Mon Jan 26 13 58 24 EST 2009 x86 64 x86 64 x86 64 GNU Linux   For this test  at least  it looks like sed is slower than the tail approach  27 sec vs   14 sec

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Perl approach   perl -ne  if  i lt 1000    print    else   print STDERR     i     in 1 gt  in new 2 gt  out  amp  amp  mv in new in

User · Answer

This is a one-liner but uses four atomic commands   head -1000 file txt  gt  newfile txt  tail  1000 file txt  gt  file txt tmp  cp file txt tmp file txt  rm file txt tmp

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Using pipe   cat en-tl 100 en   head -10

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head -1000 input  gt  output  amp  amp  sed -i  1  999d  input   For example     cat input  1 2 3 4 5 6   head -3 input  gt  output  amp  amp  sed -i  1  2d  input   cat input  4 5 6   cat output  1 2 3

User · Answer

head -1000 file txt  gt  first100lines txt tail --lines  1001 file txt  gt  restoffile txt

[unix] Move top 1000 lines from text file to a new file using Unix shell commands

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