Differences between revisions 36 and 39 (spanning 3 versions)
⇤ ← Revision 36 as of 2018-12-21 20:47:27 →
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Editor: Valentin Bajrami
Comment: Another method of printing a line using -n and p flag with sed.
← Revision 39 as of 2020-05-07 08:35:17 → ⇥
Size: 1685
Editor: intranet
Comment: fix awk code injection
Deletions are marked like this. Additions are marked like this.
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There is yet another simple way of printing only the line you want using `sed`. The "-n" option will not print anything unless `p` flag is explicitly specified. For example to print the 4th line in a file use.

{{{#!highlight bash
sed -n "4p" "$file"
}}}
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awk "NR==$n{print;exit}" "$file" awk -v n="$n" 'NR==n{print;exit}' "$file"
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awk "NR>=$x{print} NR==$y{exit}" "$file" # Same awk -v x="$x" -v y="$y" 'NR>=x{print} NR==y{exit}' "$file" # Same

How can I print the n'th line of a file?

One dirty (but not quick) way is: 

   1 sed -n "${n}p" "$file"

But this reads the entire file even if only the third line is desired, which can be avoided by using the q command to quit on line $n, and deleting all other lines with the d command: 

   1 sed "${n}q;d" "$file"

Another method is to grab lines starting at n, then get the first line of that. 

   1 tail -n "+$n" "$file" | head -n 1

Another approach, using AWK: 

   1 awk -v n="$n" 'NR==n{print;exit}' "$file"

If more than one line is needed, it's easy to adapt any of the previous methods: 

   1 x=3 y=4
   2 sed -n "$x,${y}p;${y}q;" "$file"                # Print lines $x to $y; quit after $y.
   3 head -n "$y" "$file" | tail -n "$((y - x + 1))"   # Same
   4 head -n "$y" "$file" | tail -n "+$x"            # If your tail supports it
   5 awk -v x="$x" -v y="$y" 'NR>=x{print} NR==y{exit}' "$file"        # Same

Or a counter with a simple read loop: 

   1 # Bash/ksh
   2 m=0
   3 while ((m++ < n)) && read -r _; do
   4     :
   5 done
   6 
   7 head -n 1

To read into a variable, it is preferable to use read or mapfile rather than an external utility. More than one line can be read into the given array variable or the default array MAPFILE by adjusting the argument to mapfile's -n option: 

   1 # Bash4
   2 mapfile -ts "$((n - 1))" -n 1 x <"$file"
   3 printf '%s\n' "$x"

See Also

CategoryShell

BashFAQ/011 (last edited 2020-05-07 08:35:17 by intranet)