awk - How to print the number of characters for the first n lines in a file?

command-line text-processing awk

8,632

Solution 1

Tell awk to quit when enough lines have been read:

awk '$0 = length; NR==3 { exit }' /etc/passwd

Note that this solution ignores empty lines, although not for the line count.

Solution 2

A direct Awk version (not so efficient as @Thor's), but slightly more clear:

awk 'NR <= 3 {print length}' /etc/passwd

Solution 3

You can execute it with awk only command, as nicely described by @Thor, and @JJoao (+1 from me)

You can combine awk and head with parameter -n follows by the number of lines as described below:

Thanks for @Maerlyn suggestion to execute in this order: head | awk

e.g. You will get the first 3 lines using:

head -n3 /etc/passwd | awk '{ print length($0); }'

head man

-n, --lines=[-]K
    print the first K lines instead of the first 10; with the leading '-', print all but the last K lines of each file

8,632

bambosze_babuni

Updated on September 18, 2022

Comments

bambosze_babuni over 1 year
I have a command:
```
$ awk '{ print length($0); }' /etc/passwd
```
It prints number of characters of every line in a passwd file:
```
52
52
61
48
81
58
etc.
```
How can I print the number of characters for only the first n lines?

For example - for the first 3 lines it would give something like:
```
52
52
61
```
- njzk2 about 7 years
  
  @ilkkachu true.
- VIPIN KUMAR about 7 years
  
  If you want to ignore blank like then use below - awk '(NR<=line) && length($0) {print length($0)}' line=3 file
Yaron about 7 years

@msjavx86 - great :) please accept the answer, when you'll be able to do it
bambosze_babuni about 7 years

of course I will - in about 10 minutes ;) thanks again!
Admin about 7 years

tricky and cool! (+1)
Maerlyn about 7 years

Maybe even reverse, head -n3 /etc/passwd | awk so awk doesn't have to process the whole file.
ilkkachu about 7 years

If any or the lines is empty, the assignment evaluates to zero (a falsy value), and the length will not be printed.
Dennis Williamson about 7 years

If this was awk '{ print length } NR>=3 { exit }' /etc/passwd, I'd upvote it.
Dennis Williamson about 7 years

AWK can count lines, no need for head.
Admin about 7 years

@DennisWilliamson, thank you. That is a very good suggestion, I will not include it in my answer because it is already implicit in Thor's proposal.
Thor about 7 years

@ilkkachu: Depending on the situation, it would be reasonable to ignore empty lines. I have added a note about this.
Yaron about 7 years

@DennisWilliamson - thanks for the comment, using head was the first working solution which came to my mind. I've upvoted @Thor, @JJoao answer which uses awk only solution.