How to Read a File in Bash: Simple Commands and Examples

In bash, you can read a file line by line using a while loop combined with read. Alternatively, use cat filename to display the whole file content at once.

Syntax

Here is the basic syntax to read a file line by line in bash:

• while read line; do - starts a loop reading each line into the variable line
• commands - commands to process each line
• done < filename - ends the loop and redirects the file as input

bash

while read line; do
  echo "$line"
done < filename.txt

Example

This example reads a file named example.txt line by line and prints each line with a prefix.

bash

while read line; do
  echo "Line: $line"
done < example.txt

Output

Line: Hello
Line: This is a file
Line: Read line by line

Common Pitfalls

Common mistakes when reading files in bash include:

• Not redirecting the file into the while loop, causing it to wait for keyboard input.
• Using read without quotes, which can cause word splitting and lose spaces.
• Trying to read a file with spaces or special characters without proper quoting.

bash

Wrong way:
while read line; do
  echo $line
 done
# This waits for keyboard input instead of reading a file

Right way:
while read line; do
  echo "$line"
done < filename.txt

Quick Reference

Command	Description
while read line; do ... done < file	Read file line by line safely
cat file	Print entire file content
read -r line	Read line without interpreting backslashes
echo "$line"	Print line preserving spaces

Key Takeaways

Use a while loop with read and file redirection to read files line by line.

Always quote variables like "$line" to preserve spaces and special characters.

Redirect the file into the loop using done < filename to avoid waiting for keyboard input.

Use cat filename for quick full file display but prefer loops for processing lines.

Use read -r to prevent backslash escapes from being interpreted.