if i have a .gz file on unix which has certain number of lines. How could i count the lines on unix without uncompressing it.
You can obviously not count newlines if the file is still compressed.
But you can decompress to a stream, and count the newlines in that stream, without ever writing the (decompressed) file to disk. That would go something like so:
zcat file.gz | wc -l
zcat for decompress & cat, wc for wordcount. See man pages for both if you want to know more.
If you do not have zcat, zcat is just another name for
This also seems to work - grep for the number of line-endings in the file
zgrep -Ec "$" file.gz
If you want to do it quickly, I recommend using 'pigz' (which IIRC stands for "Parallel Implementation of GZip"). I just had a similar situation where I wanted to count the number of lines in a bunch of gzip'ed files and here was my solution:
for x in *.gz; do unpigz -p 8 -c $x | wc -l && echo $x; done
Which gave me the number of lines and the file it counted from on alternating lines, using 8 processors. It ran quickly!
Use this command:
gzgrep -c $ filename.gz
gzgrep behaves the same as
grep but on gzip compressed files. It decompress the file on the fly for the regex matching.
In this case
-c instruct the command to output number of matched lines and the regex
$ matches end of line so it matches every line or the file.
The final result is identical to
gzip -dc filename.gz | grep -c $.
If you're okay with a rough estimate rather than an exact count, and actually extracting the whole file or zgrepping it for line endings would both take much too long (which was my situation just now), you can:
zcat "$file" | head -1000 > 1000-line-sample.txt ls -ls 1000-line-sample.txt "$file"
then the approximate line count is
1000 * (size of $file) / (size of 1000-line-sample), as long as your data is fairly homogeneous per line.