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` 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 2
Line 3
Line 4
Running the command:
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:
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:
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.
