How do I read the first line of a file using cat?

Question

How do I read the first line of a file using cat?

score 574 · Accepted Answer · edited Sep 27 '19 at 15:34

574

You don't need cat.

head -1 file

will work fine.

edited Sep 27 '19 at 15:34

Akaisteph7

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answered May 24 '11 at 17:06

Carl Norum

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+1. you only need the head not the whole cat :P (the command tail is part of the bash pun too) – SparK Feb 17 '14 at 18:54
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Does `head` read the entire file and cut it, or does it read only the 1 line? – CMCDragonkai May 01 '15 at 02:53
@CMCDragonkai, I guess you could check the [source](http://git.savannah.gnu.org/cgit/coreutils.git/tree/src/head.c). – Carl Norum May 01 '15 at 03:47
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I guess it reads only first lines - it opens a hundreds-megabytes file in milliseconds. – Brian Cannard Sep 14 '15 at 14:21
What about if your were catting multiple files? e.g. I want to achieve `cat file1 file2 | head` without reading all of `file1` and `file2`? – James Owers Oct 28 '15 at 14:02
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...got it! `cat <(head file1) <(head file2)`. [Source](http://www.commandlinefu.com/commands/view/1385/cat-stdout-of-multiple-commands) – James Owers Oct 28 '15 at 14:07
I'm not sure if this is a Mac-specific thing, but the command is `head -n 1 file`. There is a `-n` argument to pass the number of lines with. – Gustavo Straube Aug 25 '16 at 10:49
`head -1 *.txt` would work too to find first line of all text files – a7md0 Oct 04 '22 at 19:35

score 93 · Answer 2 · answered May 24 '11 at 17:07

93

You don't, use head instead.

head -n 1 file.txt

answered May 24 '11 at 17:07

Orbling

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score 48 · Answer 3 · answered Jul 06 '12 at 12:17

48

There are many different ways:

sed -n 1p file
head -n 1 file
awk 'NR==1' file

answered Jul 06 '12 at 12:17

JJJ

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And when should we use which? – Xanlantos Jun 11 '21 at 12:06

score 26 · Answer 4 · answered May 24 '11 at 17:07

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You could use cat file.txt | head -1, but it would probably be better to use head directly, as in head -1 file.txt.

answered May 24 '11 at 17:07

Mike Pelley

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Thank you for actually answering the question! – Akaisteph7 Jun 23 '23 at 15:23

score 17 · Answer 5 · answered May 24 '11 at 17:07

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This may not be possible with cat. Is there a reason you have to use cat?

If you simply need to do it with a bash command, this should work for you:

head -n 1 file.txt

answered May 24 '11 at 17:07

mwcz

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score 12 · Answer 6 · answered May 24 '11 at 17:16

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cat alone may not be possible, but if you don't want to use head this works:

 cat <file> | awk 'NR == 1'

answered May 24 '11 at 17:16

josh.trow

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I suppose it's silly to call out a 'useless use of cat' on a line specifically designed to use `cat`, isn't it. – jkerian May 24 '11 at 19:20
This method is great because you can pick any line you want. – desgua Nov 28 '13 at 09:14
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@desgua `awk` is great, but you don't need `cat` here. `awk 'NR == 2 {print $0}' ` does the same thing. (And much more, if you learn a little `awk`. – Eric Wilson Jun 25 '15 at 13:36

Charles Duffy · Answer 7 · 2014-02-17T19:07:17.573

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I'm surprised that this question has been around as long as it has, and nobody has provided the pre-mapfile built-in approach yet.

IFS= read -r first_line <file

...puts the first line of the file in the variable expanded by "$first_line", easy as that.

Moreover, because read is built into bash and this usage requires no subshell, it's significantly more efficient than approaches involving subprocesses such as head or awk.

edited Feb 17 '14 at 19:07

answered Feb 17 '14 at 18:50

Charles Duffy

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what's the `IFS=` part at the beginning? – Florian Castellane May 24 '18 at 11:53
my bad, here is an explanation: https://unix.stackexchange.com/questions/184863/what-is-the-meaning-of-ifs-n-in-bash-scripting – Florian Castellane May 24 '18 at 12:01
Right; in this case, clearing `IFS` prevents leading and trailing whitespace from being stripped from the string that's read. – Charles Duffy May 24 '18 at 15:39

score 3 · Answer 8 · edited Dec 16 '19 at 17:46

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Use the below command to get the first row from a CSV file or any file formats.

head -1 FileName.csv

edited Dec 16 '19 at 17:46

Yogi Ghorecha

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answered Jul 26 '18 at 08:01

Praveenkumar Sekar

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score 3 · Answer 9 · answered May 24 '11 at 19:16

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You dont need any external command if you have bash v4+

< file.txt mapfile -n1 && echo ${MAPFILE[0]}

or if you really want cat

cat file.txt | mapfile -n1 && echo ${MAPFILE[0]}

:)

answered May 24 '11 at 19:16

clt60

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score 2 · Answer 10 · answered Sep 24 '20 at 12:51

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There is plenty of good answer to this question. Just gonna drop another one into the basket if you wish to do it with lolcat

lolcat FileName.csv | head -n 1

answered Sep 24 '20 at 12:51

Norfeldt

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score 0 · Answer 11 · answered Nov 03 '20 at 23:35

0

Adding one more obnoxious alternative to the list:

perl -pe'$.<=1||last' file
# or 
perl -pe'$.<=1||last' < file
# or
cat file | perl -pe'$.<=1||last'

answered Nov 03 '20 at 23:35

ardnew

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How do I read the first line of a file using cat?

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