Perl oneliner: print first lines into file

Question

I want to print the first 10 lines of a huge file into a new file. With this oneliner I can print the lines on the monitor:

> perl -ne "print if $. < 10" in.csv

I tried this:

> perl -ne "print if $. < 10" in.csv >out.txt

But this does only create the file out.txt without writing the first lines into it. What is wrong with this code?
Thanks for help

Windows 7 / Strawberry Perl

Update1:
If I send the print result on monitor using:

> perl -ne "print if $. <= 10" in.csv

the program does not stop, that is, the first ten lines are output on the monitor but it does not end with:

I have to stop the program using Ctrl+c.

Using the simple csv-File like ikegami (just some rows) the onliner works. I assume there is something within the csv-file.

Update 2:
The original onliner:

> perl -ne "print if $. <= 10" in.csv >out.txt

works. I have to wait some seconds. The csv-file is 2 GB large. The onliner:

> perl -pe "exit if $. > 10" in.csv >out.txt

gives the result immediately. Conclusion: the first onliner goes through all rows, the second exit after 10 rows.

Sorry that I bother you with this problem. I learnt my lesson: use an appropriate onliner or wait some more seconds.

It works for me as-is on win2k8r2. Is the output file being set to read-only after its initial creation? — stevieb, Jun 04 '15 at 17:26
@stevieb. No. It can be written. I tried the example of ikegami and it works. Obviously, it has something to do with the original csv-file. — giordano, Jun 05 '15 at 06:12

ikegami · Answer 1 · 2015-06-05T13:47:51.327

2

hum? That's correct (except < 10 should be <= 10):

>type in.csv
a
b
c
d
e
f
g
h
i
j
k
l
m
n
...
z

>perl -ne "print if $. <= 10" in.csv >out.txt

>type out.txt
a
b
c
d
e
f
g
h
i
j

>

A faster solution would exit when it has no more to print rather than printing the entire file.

perl -pe"last if $. > 10" in.csv >out.txt

edited Jun 05 '15 at 13:47

answered Jun 04 '15 at 16:59

ikegami

1

Probably no point continuing to read and discard the extra lines. How about: `perl -pe "exit if $. > 10"` ? – Grant McLean Jun 04 '15 at 21:20
Good tip. Personally, I'd use `last`. – ikegami Jun 05 '15 at 03:26
@Grant McLean Thanks!! This does work with my csv-file. Maybe you have an idea why this oneliner works and the other does not using the original file? If you put your answer as **answer** I will give you a point. – giordano Jun 05 '15 at 06:29
To all: see my answer in Update 2. – giordano Jun 05 '15 at 06:39

1 Answers1