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| The dirty (but not quick) way would be {{{sed -n ${n}p "$file"}}} but this reads the whole input file, even if you only wanted the third line. | One dirty (but not quick) way is: |
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| The following {{{sed}}} command line reads a file printing nothing (-n). At line $n the command "p" is run, printing it, with a "q" afterwards: quit the program. {{{ sed -n "$n{p;q;}" "$file" |
{{{#!highlight bash sed -n "${n}p" < "$file" |
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| Another way, more obvious to some, is to grab the last line from a listing of the first n lines: {{{ head -n $n $file | tail -n 1 |
But this reads the entire file even if only the third line is desired, which can be avoided by using the `q` command to quit on line `$n`, and deleting all other lines with the `d` command: {{{#!highlight bash sed "${n}q;d" < "$file" |
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| Using awk: {{{ awk 'NR==n{print;exit}' file |
Or {{{#!highlight bash sed "$n!d;q" < "$file" |
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Which appears to be faster with all of GNU, busybox and ast-open sed implementations. Another method is to grab lines starting at `n`, then get the first line of that. {{{#!highlight bash <"$file" tail -n "+$n" | head -n 1 }}} As that uses more specialized tools, that's generally generally significantly faster. Another approach, using [[AWK]]: {{{#!highlight bash 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: {{{#!highlight bash x=3 y=4 sed "$x,$y!d;${y}q" < "$file" # Print lines $x to $y; quit after $y. tail -n "+$x" < "$file" | head -n "$(( y - x + 1 ))" # Same, generally faster awk -v x="$x" -v y="$y" 'NR>=x; NR==y{exit}' < "$file" # Same, generally slower }}} Or a counter with a simple `read` loop, though that's going to be orders of magnitude slower for any input with more than a few hundred lines. {{{#!highlight bash # Bash/ksh/zsh { m=0 while ((m++ < x - 1)) && read -r _; do : done head -n "$((y - x + 1))" } < "$file" }}} To read into a variable, it is preferable to use `read` or `mapfile` aka `readarray` rather than an external utility. More than one line can be read into the given array variable or the default array `MAPFILE` by adjusting the argument to mapfile's -n option: {{{#!highlight bash # Bash4 { mapfile -s "$((x - 1))" -n "$((y - x + 1))" lines printf %s "${lines[@]}" } < "$file" }}} === See Also === * [[BashFAQ/001]] * http://wiki.bash-hackers.org/commands/builtin/mapfile ---- CategoryShell |
How can I print the n'th line of a file?
One dirty (but not quick) way is:
1 sed -n "${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" < "$file"
Or
1 sed "$n!d;q" < "$file"
Which appears to be faster with all of GNU, busybox and ast-open sed implementations.
Another method is to grab lines starting at n, then get the first line of that.
1 <"$file" tail -n "+$n" | head -n 1
As that uses more specialized tools, that's generally generally significantly faster.
Another approach, using AWK:
1 awk -v n="$n" 'NR==n{print;exit}' < "$file"
If more than one line is needed, it's easy to adapt any of the previous methods:
Or a counter with a simple read loop, though that's going to be orders of magnitude slower for any input with more than a few hundred lines.
To read into a variable, it is preferable to use read or mapfile aka readarray 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: