Viewing and inspecting file contents

A terminal user should be able to look inside any file without leaving the command line.

Print a file — cat

cat README.md

cat reads a file and prints it to the terminal. It is fast and simple.

cat file1.txt file2.txt    # concatenate and print multiple files
cat -n file.txt            # show line numbers

For large files, cat scrolls too fast to read. Use less instead.

Page through a file — less

less large-file.txt

less opens a file in a scrollable viewer. This is the right tool for anything bigger than a screenful.

Navigation:

• j / k or arrow keys — scroll down / up
• Space — page down
• b — page up
• g — go to the top
• G — go to the bottom
• /pattern — search forward
• q — quit

View the beginning or end — head and tail

head file.txt          # first 10 lines
head -n 20 file.txt    # first 20 lines

tail file.txt          # last 10 lines
tail -n 5 file.txt     # last 5 lines

Following live logs with tail -f

tail -f server.log

tail -f keeps the file open and prints new lines as they are appended. This is how you watch a log file in real time.

Stop with Ctrl-C.

Count lines, words, characters — wc

wc file.txt            # lines, words, bytes
wc -l file.txt         # just lines
wc -w file.txt         # just words
wc -c file.txt         # just bytes

Useful for quick checks:

wc -l access.log       # how many log entries?

What kind of file is this? — file

file image.png
file script.sh
file data.bin

file inspects a file’s contents (not just the extension) and reports what type it is.

image.png:  PNG image data, 800 x 600, 8-bit/color RGBA
script.sh:  POSIX shell script, ASCII text executable
data.bin:   data

This is useful when an extension is missing or misleading.

File metadata — stat

stat file.txt

stat shows metadata: file size, permissions, owner, creation time, modification time.

  File: file.txt
  Size: 1234        Blocks: 8          IO Block: 4096   regular file
  Access: 2025-01-15 10:30:00.000000000 +0000
  Modify: 2025-01-14 09:00:00.000000000 +0000
  Change: 2025-01-14 09:00:00.000000000 +0000

Line endings: plain text vs binary

Text files use invisible characters to mark line endings:

• Unix (macOS, Linux): LF (\n)
• Windows: CRLF (\r\n)

This usually does not matter, but it can cause issues when scripts written on one platform run on another. If a script fails with “bad interpreter” or strange ^M characters appear in output, line endings are likely the cause.

Binary files (images, compiled programs, archives) should not be printed with cat — they will produce garbled output. Use file to identify them first.

The main idea to carry forward

Use the right viewer for the job: cat for small files, less for anything larger, head/tail for the edges, tail -f for live logs, wc for counts, file for type identification, and stat for metadata. These tools give you complete visibility into any file.