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Step 3 — Searching & Text Viewing (Ubuntu 24)

Type along exactly as shown. This step is written for absolute beginners and assumes no prior Linux experience.
Estimated time: ~10–15 minutes

What you’ll learn

How to view text files (cat, less, head, tail)
How to search inside files with grep
How to find files/folders anywhere with find
How to chain commands together with the pipe (|) for quick analysis
How to avoid common mistakes (case, spaces, patterns)

This expands the original brief step to include practical variations, safety notes, and troubleshooting.

Setup: Continue using your practice area from previous steps (recommended):
mkdir -p ~/playground && cd ~/playground

0) Create some sample files to search

We’ll set up a few files so your searches have something to find.

cd ~/playground
echo "Hello Linux" > hello.txt
echo "hello again" >> hello.txt
echo "Linux is powerful" > notes.txt
echo "HELLO CAPS" > caps.txt
mkdir -p logs
printf "alpha\nbeta\ngamma\nBeta\nGamma\n" > logs/mixed.txt

Verify:

ls -l
ls -l logs

1) View files quickly (`cat`) and with scrolling (`less`)

A) View entire file now:

cat hello.txt

cat prints the file to your screen immediately (great for short files).

B) Scroll through long files:

less notes.txt

Keys: Up/Down or PageUp/PageDown to move; /word to search; n for next match; q to quit.
less doesn’t load the whole file at once — it’s ideal for big files and logfiles.

C) Peek at the top/bottom only (useful for logs):

head -n 3 hello.txt   # first 3 lines
tail -n 3 hello.txt   # last 3 lines
tail -f hello.txt     # follow new lines live; press Ctrl+C to stop

Tip: Use tail -f while another process writes to a log to watch updates in real time.

2) Search inside files with `grep`

grep finds lines containing a pattern.

A) Basic search (case-sensitive by default):

grep "Hello" hello.txt

Matches Hello but not hello.

B) Case-insensitive search:

grep -i "hello" hello.txt

C) Show line numbers with matches:

grep -n "hello" hello.txt

D) Search multiple files at once:

grep -n "linux" *.txt

Matches lines containing linux in any .txt file (case-sensitive).

E) Recursive search (search through folders):

grep -Rni "beta" .

-R = recursive, -n = show line numbers, -i = ignore case

F) Show only the filenames that match:

grep -Rl "hello" .

G) Regex (advanced but useful):
Match Hello or HELLO or hello without -i, using an extended regex:

grep -En "(?i)hello" *.txt 2>/dev/null || grep -En "(H|h)ELLO|Hello|hello" *.txt 2>/dev/null

Note: The (?i) flag is not supported in all grep versions; the fallback demonstrates alternation with -E. Beginners can skip this for now.

H) Invert match (show lines that do not match):

grep -v "hello" hello.txt

3) Find files/folders anywhere with `find`

find walks directories and lets you filter by name, type, size, time, and more.

A) Find by name:

find . -name "hello.txt"
find . -name "*.txt"

B) Only files vs. only directories:

find . -type f -name "*.txt"
find . -type d -name "logs"

C) Limit depth to current folder only:

find . -maxdepth 1 -type f -name "*.txt"

D) Find by size (files larger than 1 megabyte):

find . -type f -size +1M

E) Find by modified time (edited within last 1 day):

find . -type f -mtime -1

F) Do something with each result (-exec):
Show file sizes for all .txt files:

find . -type f -name "*.txt" -exec wc -l {} \;

wc -l counts lines; {} is replaced by each found file; \; ends the -exec command.

G) Safer piping with null terminators (handles spaces in filenames):

find . -type f -name "*.txt" -print0 | xargs -0 grep -n "hello"

This combination searches all .txt files for hello, even if filenames contain spaces.

4) Combine tools with the pipe `|`

A) Quick counts (how many matches?):

grep -Rni "hello" . | wc -l

wc -l counts how many matching lines were found.

B) Sort and unique (e.g., see unique matching filenames):

grep -Rl "hello" . | sort | uniq

C) Show the 5 most common words in a file (simple demo):

tr -cs '[:alnum:]' '\n' < hello.txt | tr '[:upper:]' '[:lower:]' | sort | uniq -c | sort -nr | head -n 5

Splits text into words, lowercases, counts, and shows top 5.

Note: The above is a mini data-processing pipeline — not required for beginners but fun to see what’s possible.

5) Practice tasks (do them now)

Show the first 2 lines of logs/mixed.txt.
Show only the lines that contain “Gamma” (any case) in logs/mixed.txt.
Find all .txt files in this folder only (not subfolders).
Count how many lines in all .txt files mention “hello” (any case).
Show the filenames only that contain the word “Linux” (case-insensitive) anywhere under the current folder.

Hints:

head -n 2 logs/mixed.txt
grep -i "gamma" logs/mixed.txt
find . -maxdepth 1 -type f -name "*.txt"
grep -Rni "hello" . | wc -l
grep -Rli "linux" .

Troubleshooting

Q: grep: *.txt: No such file or directory
A: Wildcards expand before grep runs. If nothing matches *.txt, your shell might pass the literal string. Make sure you’re in the right folder and that .txt files exist.

Q: My search is case-sensitive, but I need any case.
A: Add -i to grep (e.g., grep -i "hello").

Q: find prints “Permission denied”.
A: You’re walking directories you don’t own (outside your home). For practice, stay inside ~/playground.

Q: less won’t quit.
A: Press q to exit less.

Quick Quiz (1 minute)

Which command opens a scrollable viewer?
How do you search recursively and ignore case with grep?
How do you show only filenames that match?
Which find option restricts search to current directory only?
What does wc -l do when piped after grep?

Answers: less; grep -Rni "term" .; grep -Rl "term" .; -maxdepth 1; counts matching lines.

Next Step

Continue to Step 4 — Process Management to learn how to view, sort, and control running programs.

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