Reading Lines From Files in bash

In Bash, you can read lines from files using various methods. Here are a few examples:

1. Using while loop and read command:

#!/bin/bash

# Read lines from a file using a while loop
while IFS= read -r line; do
    echo "Line: $line"
done < "file.txt"

In this example, the while loop reads each line from the file “file.txt” using the read command. The -r option prevents backslashes from being interpreted as escape characters, and IFS= ensures that leading and trailing whitespace is preserved. The loop body can be customized to perform actions on each line.

2. Using a for loop and input redirection:

#!/bin/bash

# Read lines from a file using a for loop
for line in $(< "file.txt"); do
    echo "Line: $line"
done

In this example, the for loop iterates over each word in the file “file.txt” using command substitution $(< "file.txt"). The loop treats each line as a separate word, which may not be desirable if lines contain spaces. However, it can be useful in certain scenarios.

3. Using mapfile command (requires Bash version 4 or later):

#!/bin/bash

# Read lines from a file using mapfile
mapfile -t lines < "file.txt"

# Process each line
for line in "${lines[@]}"; do
    echo "Line: $line"
done

In this example, the mapfile command reads the lines of the file “file.txt” into an array named lines. The -t option removes trailing newline characters. Subsequently, a for loop iterates over each line in the array and performs the desired actions.

These examples demonstrate different approaches for reading lines from a file in Bash. Choose the method that suits your specific requirements and adapt it as needed for your script.