1793
Comment: Quotes
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← Revision 39 as of 2020-05-07 08:35:17 ⇥
1685
fix awk code injection
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Deletions are marked like this. | Additions are marked like this. |
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{{{ | {{{#!highlight bash |
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But this reads the entire file even if only the third line is desired, which can be avoided by printing line `$n` using the `p` command, followed by a `q` to exit the script: | But this reads the entire file even if only the third line is desired, which can be avoided by using the `q` command to quit on line `$n`, and deleting all other lines with the `d` command: |
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{{{ sed -n "$n{p;q;}" "$file" |
{{{#!highlight bash sed "${n}q;d" "$file" |
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Another method is to grab the last line from a listing of the first `n` lines: | Another method is to grab lines starting at `n`, then get the first line of that. |
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{{{ head -n "$n" "$file" | tail -n 1 |
{{{#!highlight bash tail -n "+$n" "$file" | head -n 1 |
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{{{ awk "NR==$n{print;exit}" "$file" |
{{{#!highlight bash awk -v n="$n" 'NR==n{print;exit}' "$file" |
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{{{ | {{{#!highlight bash |
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head -n "$y" "$file" | tail -n $((y - x + 1)) # Same | head -n "$y" "$file" | tail -n "$((y - x + 1))" # Same |
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awk "NR>=$x{print} NR==$y{exit}" "$file" # Same }}} In Bash 4, `mapfile` can be used similarly to `head` while avoiding buffering issues in the event input is a pipe, because it guarantees the [[ FileDescriptor|fd ]] will be seeked to where you left it: {{{ # Bash4 { mapfile -n "$n"; head -n 1; } <"$file" |
awk -v x="$x" -v y="$y" 'NR>=x{print} NR==y{exit}' "$file" # Same |
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{{{ | {{{#!highlight bash |
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{{{ | {{{#!highlight bash |
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mapfile -ts $((n-1)) -n 1 x <"$file" | mapfile -ts "$((n - 1))" -n 1 x <"$file" |
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:
Or a counter with a simple read loop:
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: