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Size: 1319
Comment: added simpler head|tail alternative for multiple lines
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Size: 1538
Comment: Agree with Lhunath - rm useless note. Fix writing style.
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| The dirty (but not quick) way would be: | One dirty (but not quick) way is: |
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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: | |
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| but this reads the whole input file, even if you only wanted the third line. This one avoids that problem: |
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| Another method is to grab the last line from a listing of the first {{{n}}} lines: | |
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| At line $n the command "p" is run, printing it, with a "q" afterwards: quit the program. | {{{ head -n $n $file | tail -n 1 }}} Another approach, using [[AWK]]: |
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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 }}} Another approach, using [[AWK]]: |
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If you want more than one line, it's pretty easy to adapt any of the previous methods: |
If more than one line is needed, it's easy to adapt any of the previous methods: |
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| head -n $y "$file" | tail -n $(($y - $x + 1)) # Same head -n $y "$file" | tail -n +$x # even simpler |
head -n $y "$file" | tail -n $((y - x + 1)) # Same head -n $y "$file" | tail -n +$x # If your tail supports it |
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| In Bash 4, a pure-bash solution can be achieved succinctly using the {{{mapfile}}} builtin. More than one line can be read into the array {{{MAPFILE}}} by adjusting the argument to mapfile's -n option: | |
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| === Note === In most cases, you should sanitize your variable n to be sure, that it's not containing any of non-digits, before feeding it to sed or awk. You can do it with such simple code: |
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| # Bash n=${n//[!0-9]/} |
mapfile -ts $((n-1)) -n 1 < "$file" echo "${MAPFILE[0]}" }}} {{{mapfile}}} can also be used similarly to {{{head}}} while avoiding buffering issues in the event input is a pipe: |
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| # POSIX n=$(printf "%s" "$n"|tr -cd '0-9') |
{{{ { mapfile -n $n; head -n 1; } <"$file" |
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=== See Also === * [[BashFAQ/001]] * http://wiki.bash-hackers.org/commands/builtin/mapfile |
How can I print the n'th line of a file?
One dirty (but not quick) way is:
sed -n ${n}p "$file"But this reads the entire file even if only the third line is desired, which can be avoided by printing line $n using the "p" command, followed by a "q" to exit the script:
sed -n "$n{p;q;}" "$file"Another method is to grab the last line from a listing of the first n lines:
head -n $n $file | tail -n 1
Another approach, using AWK:
awk "NR==$n{print;exit}" fileIf more than one line is needed, it's easy to adapt any of the previous methods:
x=3 y=4
sed -n "$x,${y}p;${y}q;" "$file" # Print lines $x to $y; quit after $y.
head -n $y "$file" | tail -n $((y - x + 1)) # Same
head -n $y "$file" | tail -n +$x # If your tail supports it
awk "NR>=$x{print} NR==$y{exit}" "$file" # SameIn Bash 4, a pure-bash solution can be achieved succinctly using the mapfile builtin. More than one line can be read into the array MAPFILE by adjusting the argument to mapfile's -n option:
mapfile -ts $((n-1)) -n 1 < "$file"
echo "${MAPFILE[0]}"mapfile can also be used similarly to head while avoiding buffering issues in the event input is a pipe:
{ mapfile -n $n; head -n 1; } <"$file"