Counting empty lines in a file

Counting empty lines in a file

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

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

    cat > file.txt << EOL
    Line 1 Line 2 Line 3 Line 4
    EOL
    
  2. 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.
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  1. 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
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Running the command:

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

3
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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
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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
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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.


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