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I need to extract a certain line number from a file and then append it another file. New with bash,Please help!

Shivam Saxena
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2 Answers2

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head -n<SkipLines> <filename> | tail -n<TakeLines>

so if you want to take 2 lines from the 10th of a file pippo.txt:

head -n10 pippo.txt | tail -n2

EDIT:

To append it to another file just do:

head -n<SkipLines> <filename> | tail -n<TakeLines> >> <OtherFile>

head -n10 pippo.txt | tail -n2 >> pippo2.txt
Stefano d'Antonio
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Assuming Bash≥4.

To extract line 42 from file inputfile and append it to file outputfile is as simple as:

# data

input=inputfile
output=outputfile
linenb=42

# get line number
mapfile -t -s $((linenb-1)) -n 1 line < "$input" || exit 1

# check that we got a line
if ((${#line[@]}==0)); then
    printf >&2 'Line %d not found in file %s\n' "$linenb" "$input"
    exit 1
fi

# append it to output file
printf '%s\n' "$line" >> "$output"

Pure Bash!

gniourf_gniourf
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  • Sounds like a little bit of an overhead loading the whole file into an array in memory just to use N lines from that file. – Andreas Louv Jun 13 '16 at 17:27
  • @andlrc: it doesn't load the whole file at all: it _skips_ the first lines (that's what the `-s` option does) and _stops after reading one line_ (that's what the `-n 1` option does). It's very efficient! – gniourf_gniourf Jun 13 '16 at 17:28
  • I see, thanks for clarifying :-) I'm gonna read up on `mapfile` – Andreas Louv Jun 13 '16 at 17:31