README.md

Select the lines N to M in a file

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Classic use-cases:
Get some fixed lines part of a file
Get lines 2 to 11 of a command output to exclude a header line ( ls -lt, etc.)

with head and tail - commands

Complexity::white_check_mark:	Efficiency::white_check_mark:
The classic method:

head -n 15 <file> | tail -n $(( 15 - 5 + 1 ))

Argument syntax variants:

head -15 <file> | tail -$(( 15 - 5 + 1 ))
head -n15 <file> | tail -n$(( 15 - 5 + 1 ))
head -n+15 <file> | tail -n $(( 15 - 5 + 1 ))

Input variant:

head -n 15 < <file> | tail -n $(( 15 - 5 + 1 ))

Unefficient variant:

cat <file> | head -n 15 | tail -n $(( 15 - 5 + 1 ))

All the content of the file is read and passed into the pipe | and another process is created for the cat command.

with head and tail + commands

Complexity::warning:	Efficiency::white_check_mark:

head -n 15 <file> | tail -n +5

Argument syntax variants:

head -n +15 <file> | tail -n +5
head -n+15 <file> | tail -n+5
head -15 <file> | tail -n +5

Input variant:

head -n 15 < <file> | tail -n +5

Unefficient variant:

cat <file> | head -n 15 | tail -n +5

All the content of the file is read and passed into the pipe | and another process is created for the cat command.

with sed command

Complexity::warning:	Efficiency::white_check_mark:

sed -n -e "5,15p" -e "15q" <file>

Argument syntax variants:

sed -e "5,15!d" -e "15q" <file>

Input variant:

sed -n -e "5,15p" -e "15q" < <file>

Unefficient variants:

sed -n "5,15p" <file>
sed "5,15!d" <file>

All the content of the file is read by the sed command.

with awk command

Complexity::warning:	Efficiency::white_check_mark:

awk 'NR >= 5 { print $0 } NR >= 15 { print $0 ; exit }' <file>

Argument syntax variants:

awk 'NR >= 5 { print $0 } NR == 15 { print $0 ; exit }' <file>
awk 'NR >= 5 && NR <=15 { print $0 } NR > 15 { exit }' <file>
awk 'NR == 15 { print $0 ; exit } NR >= 5 { print $0 } ' <file>
awk 'NR >= 15 { print $0 ; exit } NR >= 5 { print $0 } ' <file>
awk 'NR >= 5 && NR <15 { print $0 } NR ==15 { print $0 ; exit }' <file>
awk 'NR >= 5 && NR <15 { print $0 } NR >=15 { print $0 ; exit }' <file>

Input variant:

awk 'NR >= 5 { print $0 } NR >= 15 { print $0 ; exit }' < <file>

Unefficient variants:

awk 'NR >= 5 && NR <=15 { print $0 }' <file>

All the content of the file is read by the awk command.

with shell scripting

Complexity::warning:	Efficiency::warning:

Loop and read one line of the file and print it within the while, ignore the 4 first lines and exit the when the 15th line is reached.

typeset -i lineNumber=0
while read line
do
	(( lineNumber ++ ))
	if [[ "${lineNumber}" -lt 5 ]]
	then
		continue
	fi

	echo -E "${line}"
	(( lineNumber ++ ))
	if [[ "${lineNumber}" -ge 15 ]]
	then
		break
	fi
done < <file>

Interpreted shell script is less efficient than a single command.

Script variant using a file descriptor opened on the input file:

exec 3< <file>
typeset -i lineNumber=0
for lineNumber in $( seq 15 )
do
	read line <&3

  if [[ "${lineNumber}" -lt 5 ]]
	then
		continue
	fi

	echo -E "${line}"
done
exec 3<&-