48

If I use cat -n text.txt to automatically number the lines, how do I then use the command to show only certain numbered lines.

  • 1
    What do you mean with "show only certain numbered lines", can you put an expected output? – tachomi Jun 8 '16 at 19:27
  • 1
    There's probably going to be a million ways to do this. tail + head can also do this, as can awk – Bratchley Jun 8 '16 at 19:36
99

Use sed

Usage

$ cat file
Line 1
Line 2
Line 3
Line 4
Line 5
Line 6
Line 7
Line 8
Line 9
Line 10

To print one line (5)

$ sed -n 5p file
Line 5

To print multiple lines (5 & 8)

$ sed -n -e 5p -e 8p file
Line 5
Line 8

To print specific range (5 - 8)

$ sed -n 5,8p file
Line 5
Line 6
Line 7
Line 8

To print range with other specific line (5 - 8 & 10)

$ sed -n -e 5,8p -e 10p file
Line 5
Line 6
Line 7
Line 8
Line 10
23

One way of doing it is by using sed:

cat -n text.txt | sed '11d'

where 11 is the number of the line you want removed.

Or to remove all but 11:

cat -n text.txt | sed '11!d'

Ranges are also possible:

cat -n text.txt | sed '9,12!d'

And cat -n isn't even needed:

sed '9,12!d' text.txt
7

Depending on goals I like head or grep

cat /var/log/syslog -n | head -n 50 | tail -n 10

will return lines 41 thru 50.

or

cat /var/log/syslog -n | grep " 50" -b10 -a10

will show lines 40 thru 60. The problem with the grep method is that you have to use account for padding of the line numbers (notice the space)

Both are quite handy for parsing log files.

  • Neither example needs cat though – roaima Jun 9 '16 at 9:12
  • 1
    well yeah... but.... but... ..... There are better ways. The question asked about using cat though, so I used it. – coteyr Jun 9 '16 at 9:22
  • cat can't do what the OP wants – roaima Jun 9 '16 at 9:33
5

You can use awk straight up.

awk 'NR==1' file.txt

replacing '1' with the desired line number.

  • 1
    This is by a million miles the best answer here and deserves a lot more love than it has. – Wren Nov 4 '18 at 15:56
2

As others have shown you, there is no need to use cat -n. Other programs will do it for you. If, however, you really need to parse the output of cat -n and show only specific lines (for example, 4-8, 12 and 42), you could do:

$ cat -n file | awk '$1>=4 && $1<=8 || $1==12 || $1==42'
 4  Line 4
 5  Line 5
 6  Line 6
 7  Line 7
 8  Line 8
12  Line 12
42  Line 42

In awk, $1 is the first field, so this command prints all lines whose first fields are i) between 4 and 8 (inclusive) or ii) 12 or iii) 42.

If you also want to remove the field added by cat -n to get the original lines from the file, you can do:

$ cat -n file | awk '$1>=4 && $1<=8 || $1==12 || $1==42{sub(/^\s*[0-9]+\s*/,""); print}'
Line 4
Line 5
Line 6
Line 7
Line 8
Line 12
Line 42

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