HowTo: Bash For While Loop Through File Contents Script

How can I iterate through each line of a text file with Bash for or while loop under Linux or Unix like operating systems?

The best way to read a text file line by line is to use the bash while loop. The while loop syntax is as follows:


Tutorial details
Difficulty level Easy
Root privileges No
Requirements None
Est. reading time N/A

while read line
echo "$line"

In this example, read /etc/passwd file line by line using while loop:

while IFS= read -r line
  echo "$line"
done < "/etc/passwd"

Another example:

## ##
_file="${1:-/dev/null}"   #fail safe 
while IFS= read -r line
  # Do something on $line
  echo "$line"
done < "$_file"

Run it as follows:
chmod +x
./ /path/to/text/

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