Bash and Linux - Viewing and Inspecting Files

Before you begin, take a few minutes to check what you already know and how confident you feel. You will see the same questions again at the end of the module — this helps both you and us measure what you have learned. Click an option for every question and confidence rating, then click Next to continue.

You have been moving files without looking inside them. This lesson is about peeking at file contents from the terminal - whether the file is two lines or two million. You will also learn a handful of inspection commands: how big is this file, what kind of file is it, how many lines.

• Reading short files: cat.
• Reading long files without flooding your screen: less.
• Peeking at the top or bottom: head and tail.
• Counting lines, words, and characters: wc.
• Asking "what kind of file is this?": file.

cat prints a file in one go. cat is right when the file is short - say fewer than 30 lines. It is wrong for a big file: if you cat a 10,000-line log, your terminal scrolls past everything in a fraction of a second.

$ cat notes.txt

Besides, cat can also stick several files together by listing them as arguments. The name come from concatenate.

$ cd vitals
$ cat patient_001.csv patient_002.csv > two_patients.csv
$ cat two_patients.csv

less opens the file in a pager - a little reader inside your terminal where you scroll, search, and quit. It loads instantly even for huge files because it only reads what fits on screen.

$ less cohort_2026.csv

If you ever open less and cannot get out, q is the escape hatch. less -N shows line numbers, handy for config files and scripts.

There are other keywords that you may use to make browsing the file easier.

• Space or Page Down - next page.
• b or Page Up - previous page.
• j and k - down and up one line.
• g - jump to the top.
• G - jump to the bottom.
• /word - search forward; n for next match.
• ?word - search backward.
• q - quit.

Often you just want a peek at the start or end. head prints the first 10 lines; tail prints the last 10.

$ tail cohort_2026.csv

Both take -n to pick a different count:

$ head -n 5 cohort_2026.csv
$ tail -n 2 cohort_2026.csv

tail also has -f (follow). tail -f run.log keeps the file open and prints new lines as they appear - the standard way to watch a long-running job. Ctrl+C stops it.

wc (word count) reports lines, words, and characters in that order:

$ wc cohort_2026.csv
  201 201  5127 cohort_2026.csv

• wc -l - just the line count (the one you will want most often).
• wc -w - just the word count.
• wc -c - just the byte count.

wc -l answers "how many records are in this file". For a CSV with a header, remember to subtract one for the header.

$ wc -l cohort_2026.csv
201 cohort_2026.csv
# 200 patients plus a header row

$ wc cohort_2026.csv
$ wc -l cohort_2026.csv
$ wc -l notes.txt

Filenames in Linux are just labels. The .txt at the end of notes.txt is a hint, not a fact - nothing stops anyone renaming an image to mystery.txt. To learn what a file actually contains, use file. It peeks at the first few bytes and tells you what it sees.

$ file cohort_2026.csv
$ file scripts

Useful when you download something with an ambiguous name and need to know whether to cat it, unpack it, or leave it alone.

These commands are the inspection toolkit. A typical workflow when you meet an unfamiliar file:

• file the-thing - text, image, or compressed?
• wc -l the-thing - how many lines?
• head the-thing - what do the first few lines look like?
• less the-thing - scroll through it if you want more.

Later lessons chain these with pipes, but on their own they cover most "what is in this file?" questions.

You have reached the end of the module. Try the same questions again — your answers here, paired with your pre-test answers, are how we measure what the module taught you. Answer every question and confidence rating, then click Submit and see results to view your score.

Here is how your post-test answers compare with your pre-test answers. The pre/post pairing is the most reliable way to see what this module actually taught you.