README.md

Count lines of a file or any input

---

Classic use-cases:
Count lines of a single file
Count result of an input behind a pipe (|)

with wc command

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

wc -l <file> 

⚠️ The file is printed on the output by the wc command, if only the lines count is needed you can just redirect the input:

wc -l < <file> 

To suppress the file name, many unefficient variant exist:

wc -l <file>  | cut -d ' ' -f 1
wc -l <file>  | cut -d' ' -f1
wc -l <file>  | awk '{print $1}'
wc -l <file>   | sed 's/ .*//'
wc -l <file>   | sed 's/ .*$//'
wc <file>   | tr -s ' ' | cut -d ' ' -f 2
wc <file>   | tr -s ' ' | cut -d' ' -f2
wc <file>   | awk '{print $1}'
wc <file>   | tr --squeeze-repeats ' ' | cut --delimiter=' ' --fields=2
wc <file>   | awk '{print $1}'

In these command one or more process are created to execute these commands.

with sed command

Complexity::warning::warning:	Efficiency::white_check_mark:

⚠️ This commande ony work with GNU sed, use sed --version or man sed to see which version of sed is installed.

sed -n '$=' <file>

Input variant:

sed -n '$=' < <file>

with awk command

Complexity::warning:	Efficiency::white_check_mark:

awk 'END {print NR}' <file>

Syntax variant:

awk '{ lineNumber++ } END {print lineNumber}'

Input variant:

awk 'END {print NR}' < <file>

with grep command

Complexity::warning:	Efficiency::warning:

grep -c "" <file>

Argument syntax variants:

grep --count "" "${sourceFile}"

Input variant:

grep -c "" < <file>

with egrep command

Complexity::warning:	Efficiency::warning:

egrep -c "" <file>

Argument syntax variants:

egrep --count "" "${sourceFile}"

Input variant:

egrep -c "" < <file>

with perl command

Complexity::warning:	Efficiency::white_check_mark:

perl -lne 'END { print $. }' <file>

Argument syntax variants:

perl -lne'END { print $. }' <file>

Input variant:

perl -lne 'END { print $. }' < <file>

with shell scripting

Complexity::warning:	Efficiency::warning::warning:

Loop and read one line of the file to count it.

typeset -i lineNumber=0
while read line
do
	(( lineNumber ++ ))
done < <file>
echo "${lineNumber}"

Interpreted shell script is less efficient than a single command.

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

typeset -i lineNumber=0
exec 3< <file>
while read line <&3
do
	(( lineNumber ++ ))
done
exec 3<&- 
echo "${lineNumber}"

Interpreted shell script is less efficient than a single command.

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

typeset -i lineNumber=0
exec 3< <file>
while true
do
	read line <&3
	if [[ "${?}" -ne 0 ]]
	then
		break
	fi
	(( lineNumber ++ ))
done
exec 3<&-
echo "${lineNumber}" > "${targetFile}"

A test is needed after each line read which is inefficient.