How to get few lines from a .gz compressed file without uncompressing

Question

How to get the first few lines from a gziped file ? I tried zcat, but its throwing an error

zcat CONN.20111109.0057.gz|head
CONN.20111109.0057.gz.Z: A file o         


        

Answer 1

On some systems (e.g., Mac), you need to use gzcat.

Answer 2

zcat(1) can be supplied by either compress(1) or by gzip(1). On your system, it appears to be compress(1) -- it is looking for a file with a .Z extension.

Switch to gzip -cd in place of zcat and your command should work fine:

 gzip -cd CONN.20111109.0057.gz | head

Explanation

   -c --stdout --to-stdout
          Write output on standard output; keep original files unchanged.  If there are several input files, the output consists of a sequence of independently compressed members. To obtain better compression, concatenate all input files before compressing
          them.

   -d --decompress --uncompress
          Decompress.

Answer 3

This awk snippet will let you show not only the first few lines - but a range you can specify. It will also add line numbers which i needed for debugging an error message pointing to a certain line way down in a gzipped file.

gunzip -c file.gz | awk -v from=10 -v to=20 'NR>=from { print NR,$0; if (NR>=to) exit 1}'

Here is the awk snippet used in the one liner above. In awk NR is a built-in variable (Number of records found so far) which usually is equivalent to a line number. the from and to variable are picked up from the command line via the -v options.

NR>=from {
   print NR,$0; 
   if (NR>=to) 
     exit 1
}

Answer 4

On a mac you need to use the < with zcat:

zcat < CONN.20111109.0057.gz|head

Answer 5

If a continuous range of lines needs be, one option might be:

gunzip -c file.gz | sed -n '5,10p;11q' > subFile

where the lines between 5th and 10th lines (both inclusive) of file.gz are extracted into a new subFile. For sed options, refer to the manual.

If every, say, 5th line is required:

gunzip -c file.gz | sed -n '1~5p;6q' > subFile

which extracts the 1st line and jumps over 4 lines and picks the 5th line and so on.