Counting empty lines in a file

July 7, 2024

This content originally appeared on DEV Community and was authored by abbazs

Counting Empty Lines in a File Using Bash

Counting empty lines in a file can be easily done using a combination of grep and wc commands. Below is a step-by-step guide on how to do this.

Prerequisites

Basic understanding of bash commands
A file (e.g., file.txt) with some empty lines

Step-by-Step Guide

Create a Sample File (if you don’t have one already):

cat > file.txt << EOL
Line 1

Line 2

Line 3

Line 4
EOL

Command to Count Empty Lines:
The command to count empty lines is:
```
grep -v "." file.txt | wc -l
```
Let’s break down this command:

- `grep -v "." file.txt`:
    - `grep` searches for patterns within files.
    - `-v` inverts the match, so it selects non-matching lines.
    - `"."` matches any character. Therefore, `grep -v "."` matches lines that do not contain any characters (i.e., empty lines).

- `|` (pipe): Passes the output of one command as input to another command.

- `wc -l`:
    - `wc` stands for "word count".
    - `-l` counts the number of lines.

Run the Command:
Execute the command in the terminal:
```
grep -v "." file.txt | wc -l
```
The output will be the number of empty lines in the file.

Example

Given the content of file.txt:

Line 1

Line 2

Line 3

Line 4

Running the command:

grep -v "." file.txt | wc -l

Output:

This indicates there are 3 empty lines in the file.

Alternative Methods

Using `awk`:

You can also use awk to achieve the same result:

awk 'NF==0' file.txt | wc -l

Explanation:

awk 'NF==0' file.txt: awk processes each line of the file. NF stands for “Number of Fields”. If NF is 0, the line is empty.
| wc -l: Counts the number of lines output by awk.

Using `sed`:

Another way is using sed:

sed -n '/^$/p' file.txt | wc -l

Explanation:

sed -n '/^$/p' file.txt: sed stands for stream editor. -n suppresses automatic printing. /^$/ matches empty lines. p prints the matched lines.
| wc -l: Counts the number of lines output by sed.

Summary

Counting empty lines in a file can be done using several methods in bash. The grep and wc combination is a straightforward and effective way to achieve this. Alternatives like awk and sed can also be used depending on your preference and familiarity with these tools.