How to extract the first x-megabyte from a large file in unix/linux?

Question

I have a large file which I am only interested in the first couple of megabytes in the head.

How do I extract the first x-megabyte from a large file in unix/linux and put it into a seperate file?

(I know the split command can split files into many pieces. And using bash scripts I can erase the pieces I don't want. I would prefer a easier way)

[This answer](http://stackoverflow.com/questions/218912/linux-command-like-cat-to-read-a-specified-quantity-of-characters) talks about the same issue. — pareshverma91, Sep 01 '12 at 01:15

score 20 · Answer 1 · answered Jan 29 '17 at 15:42

20

Head works with binary files and the syntax is neater than dd.

head -c 2M input.file > output.file

Tail works the same way if you want the end of a file.

answered Jan 29 '17 at 15:42

Roger Heathcote

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score 18 · Accepted Answer · edited May 20 '15 at 12:54

18

E.g.

 dd if=largefile count=6 bs=1M > largefile.6megsonly

The 1M spelling assumes GNU dd. Otherwise, you could do

 dd if=largefile count=$((6*1024)) bs=1024 > largefile.6megsonly

This again assumes bash-style arithmetic evaluation.

edited May 20 '15 at 12:54

peterh

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answered Aug 31 '12 at 19:26

sehe

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score 3 · Answer 3 · answered Jul 28 '21 at 20:58

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On a Mac (Catalina) the head and tail commands don't seem to take modifiers like m (mega) and g (giga) in upper or lower case, but will take a large integer byte count like this one for 50 MB

head -c50000000 inputfile.txt > outputfile.txt

answered Jul 28 '21 at 20:58

WCBdata

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score 1 · Answer 4 · edited Aug 31 '12 at 19:25

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Try the command dd. You can use "man dd" to get main ideas of it.

edited Aug 31 '12 at 19:25

answered Aug 31 '12 at 19:24

wakensky

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How to extract the first x-megabyte from a large file in unix/linux?

4 Answers4