How to Use grep in Linux: A Practical Guide

grep searches text and shows the lines that match a pattern (a word or a regular expression). The name comes from global regular expression print. You can use it to find errors in logs, filter data, or check code quickly.

Quick commands

grep "text" file.txt          # Find lines containing "text"
grep -i "text" file.txt       # Case-insensitive match
grep -r "text" src/           # Search all files under a directory (recursively)
grep -rl "text" src/          # List filenames whose CONTENT includes "text"

find . -type f -name "*Test*"     # Filenames that CONTAIN "Test" (case-sensitive)
find . -type f -iname "*test*"    # Filenames that contain "test" (case-insensitive)

grep searches inside files.
- Use grep -rl when you want the names of files whose contents match a pattern.
- Use find ... -name/-iname when you want filenames that contain a string.

Sample files (so you can follow along)

Create three small files in your home directory:

# 1) server.log
cat > server.log <<'EOF'
2025-08-14 10:01:22 INFO  user=alice action=login
2025-08-14 10:02:05 WARN  user=bob   action=upload size=0
2025-08-14 10:03:42 ERROR user=carol action=download code=403
2025-08-14 10:05:10 INFO  user=bob   action=logout
EOF

# 2) notes.txt
cat > notes.txt <<'EOF'
Remember to back up the database on Friday.
The new server is in rack A3.
Developers should review pull requests daily.
EOF

# 3) data.csv
cat > data.csv <<'EOF'
id,name,score
1,Alice,92
2,Bob,81
3,Caroline,92
4,Ali,70
EOF

Basic usage

Find a word

grep "ERROR" server.log #Shows lines that contain ERROR.

2025-08-14 10:03:42 ERROR user=carol action=download code=403

Ignore case

grep -i "error" server.log #Matches ERROR, Error, error, etc.

2025-08-14 10:03:42 ERROR user=carol action=download code=403

Show line numbers

grep -n "upload" server.log #Helpful when you want to edit that line later.

2:2025-08-14 10:02:05 WARN  user=bob   action=upload size=0

Invert the match (show lines without the word)

$ grep -v "INFO" server.log #Useful to focus on warnings or errors only.

2025-08-14 10:02:05 WARN  user=bob   action=upload size=0
2025-08-14 10:03:42 ERROR user=carol action=download code=403

Search many files (recursive)

$ grep -r "login" . #-r searches inside subfolders too.

./server.log:2025-08-14 10:01:22 INFO  user=alice action=login

Only show the file names that match

$ grep -l "download" *.log #-l = list matching files, not the lines.

server.log

Count matches

$ grep -c "Alice" data.csv #Good for quick stats.

1

Make results easier to read

Color highlights (often on by default)

grep --color=auto -n "WARN" server.log

Show context lines around a match

grep -nC2 "ERROR" server.log   # 2 lines before and after

1-2025-08-14 10:01:22 INFO  user=alice action=login
2-2025-08-14 10:02:05 WARN  user=bob   action=upload size=0
3:2025-08-14 10:03:42 ERROR user=carol action=download code=403
4-2025-08-14 10:05:10 INFO  user=bob   action=logout


grep -nA1 "WARN" server.log    # 1 line After

2:2025-08-14 10:02:05 WARN  user=bob   action=upload size=0
3-2025-08-14 10:03:42 ERROR user=carol action=download code=403


grep -nB1 "logout" server.log  # 1 line Before

3-2025-08-14 10:03:42 ERROR user=carol action=download code=403
4:2025-08-14 10:05:10 INFO  user=bob   action=logout

Match whole words or whole lines

Whole word

grep -w "Alice" data.csv #This avoids matching “Alicea” or “Malice”.

1,Alice,92

Whole line

grep -x "Developers should review pull requests daily." notes.txt

Developers should review pull requests daily.

Fast literal search (no regex)

Sometimes you want to search exact text and skip regex rules.

grep -F "user=bob   action=upload" server.log

2025-08-14 10:02:05 WARN  user=bob   action=upload size=0

-F treats the pattern as a fixed string (faster and simpler).

Short cheat sheet

grep "text" file        # simple search
grep -i "text" file     # ignore case
grep -n "text" file     # show line numbers
grep -v "text" file     # invert match (lines without)
grep -r "text" dir/     # recursive
grep -l "text" files*   # only filenames
grep -c "text" file     # count
grep -w "word" file     # whole word
grep -x "line" file     # whole line
grep -F "a*b" file      # fixed string (no regex)
grep -E "a|b" file      # extended regex
grep -A2 -B2 "x" file   # show context

Performance & safety tips

Quote your pattern: use single quotes ‘pattern’ so the shell doesn’t expand * or ?.
Use: -F for plain text searches: faster and avoids regex confusion.
Binary files: add -I to skip or -a to treat them as text.
Locale: if you need pure byte speed, LC_ALL=C grep ... can be faster (advanced).
Color: --color=auto helps you see matches quickly.

File filters when searching directories

Include or exclude certain files as you recurse:

# Only search .log files in logs/
grep -r --include='*.log' 'ERROR' logs/

# Exclude big folders and temp files
grep -r --exclude-dir='node_modules' --exclude='*.tmp' -n 'TODO' .

# Multiple includes (repeat the flag)
grep -r --include='*.{js,ts}' --include='*.tsx' -n '\buse strict\b' src/
# (Brace expansion may be a shell feature; when unsure, repeat --include)

On many systems: -R follows symlinks, -r usually doesn’t. Check man grep for your platform.