Print every Nth line (to a maximum)

function every() { sed -n -e "${2}q" -e "0~${1}p" ${3:-/dev/stdin}; }
Thanks to knoppix5 for the idea :-) Print selected lines from a file or the output of a command. Usage: every NTH MAX [FILE] Print every NTH line (from the first MAX lines) of FILE. If FILE is omitted, stdin is used. The command simply passes the input to a sed script: sed -n -e "${2}q" -e "0~${1}p" ${3:-/dev/stdin} print no output sed -n quit after this many lines (controlled by the second parameter) -e "${2}q" print every NTH line (controlled by the first parameter) -e "0~${1}p" take input from $3 (if it exists) otherwise use /dev/stdin {3:-/dev/stdin}
Sample Output
$ seq 100000 > nums
$ every 20 150 nums 
20
40
60
80
100
120
140

$ cat nums | every 20 150
20
40
60
80
100
120
140

2
By: flatcap
2015-04-03 01:30:36

1 Alternatives + Submit Alt

  • Sometimes commands give you too much feedback. Perhaps 1/100th might be enough. If so, every() is for you. my_verbose_command | every 100 will print every 100th line of output. Specifically, it will print lines 100, 200, 300, etc If you use a negative argument it will print the *first* of a block, my_verbose_command | every -100 It will print lines 1, 101, 201, 301, etc The function wraps up this useful sed snippet: ... | sed -n '0~100p' don't print anything by default sed -n starting at line 0, then every hundred lines ( ~100 ) print. '0~100p' There's also some bash magic to test if the number is negative: we want character 0, length 1, of variable N. ${N:0:1} If it *is* negative, strip off the first character ${N:1} is character 1 onwards (second actual character). Show Sample Output


    1
    function every() { N=$1; S=1; [ "${N:0:1}" = '-' ] && N="${N:1}" || S=0; sed -n "$S~${N}p"; }
    flatcap · 2015-03-21 23:44:59 4

What Others Think

Nicely done. Wow. Too bad clf is broken atm (doesn't let me upvote and/or add to faves).
wejn · 192 weeks and 4 days ago
Thanks :-)
flatcap · 192 weeks and 4 days ago
from 50 to 150 print every 20-th line: . seq 51 150 | awk 'NR % 20 == 0' 70 90 110 130 150 . See other solutions too (sed, perl ...) http://superuser.com/questions/396536/how-to-keep-only-every-nth-line-of-a-file
knoppix5 · 192 weeks and 2 days ago
Nice
flatcap · 192 weeks and 2 days ago

What do you think?

Any thoughts on this command? Does it work on your machine? Can you do the same thing with only 14 characters?

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