Looping through the content of a file in Bash

Reading file contents line by line is a common requirement in Bash scripting. There are several approaches to accomplish this task, each with its own advantages depending on your specific needs.

Creating a Sample File

First, let's create a sample file to work with ?

# Create the file
cat > a_file.txt << EOF
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EOF

# Display the file contents
cat a_file.txt

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Using While Loop with Read

The most common and reliable method uses a while loop with the read command ?

#!/bin/bash
while read line
do 
    echo "$line"
done < a_file.txt

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Using For Loop with Command Substitution

This approach uses a for loop with command substitution to iterate through each line ?

#!/bin/bash
file="a_file.txt"
for line in $(cat $file)
do
    echo "$line"
done

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Using Echo with Command Substitution

You can display all file contents at once using echo, but this will output everything on a single line ?

echo $(< a_file.txt)

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Handling Files with Blank Lines

When your file contains blank lines, you can preserve or skip them using the Internal Field Separator (IFS) ?

#!/bin/bash
while IFS= read -r line
do 
    echo "$line"
done < a_file.txt

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Comparison of Methods

Conclusion

The while read method is the most robust approach for reading files line by line in Bash. Use IFS= read -r to preserve whitespace and handle special characters properly.