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}
$ 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
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
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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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