How to view the contents of a text file in Linux?

In Linux, several commands can be used to view the contents of a text file:

• cat filename — displays the entire file.
• less filename — paginated viewing with scrolling capability.
• more filename — similar to less, but with simpler functionality.
• head filename — shows the first 10 lines of the file.
• tail filename — shows the last 10 lines, useful for logs.

For example, to view the first 20 lines of a file:

head -n 20 filename.txt

Or to view a file with scrolling:

less filename.txt