Mastering Multiple Pattern Matching in grep: A Comprehensive Guide

Introduction

grep is a representative command for string searching on Linux and macOS.

In particular, being able to handle multiple patterns allows you to streamline log analysis and configuration file verification.

This article explains grep's multiple pattern search from the basics to practical use in an easy-to-understand way.

Reference: GNU grep

How to Write Basic Searches Using Multiple Patterns with grep

Creating the File

cat << 'EOF' > input.txt
apple orange banana
grape apple melon
banana kiwi orange
melon grape lemon
EOF

Command to Run

grep -E 'apple|banana' input.txt

Output

apple orange banana
grape apple melon
banana kiwi orange

Command to Run

grep -e 'orange' -e 'grape' input.txt

Output

apple orange banana
grape apple melon
banana kiwi orange
melon grape lemon

How It Works

Syntax	How It Works	Example
grep -E 'A|B'	OR search using multiple patterns separated by |	grep -E 'apple|banana' input.txt
grep -e pattern1 -e pattern2	Search by specifying multiple -e flags	grep -e 'orange' -e 'grape' input.txt

Explanation

grep allows multiple conditions to be treated as an OR search.
Using -E with regular expressions and specifying multiple -e flags are the fundamental approaches.

How to OR Search Multiple Strings Using Multiple Patterns with grep

Creating the File

cat << 'EOF' > input.txt
apple
banana
orange
grape
pineapple
EOF

Command to Run

grep -E 'apple|orange' input.txt

Output

apple
orange
pineapple

Command to Run

grep -e 'banana' -e 'grape' input.txt

Output

banana
grape

How It Works

Method	Example Command	How It Works
Using -E	grep -E 'apple|orange' input.txt	Specify OR conditions using |
Using multiple -e flags	grep -e 'banana' -e 'grape' input.txt	Add search conditions with each -e flag and display lines matching any of them

Explanation

With grep, using -E and | allows concise OR searches.
Also, specifying multiple -e flags enables multi-condition searches with high readability.

How to Use and Distinguish Between the -E Option and egrep for Multiple Patterns with grep

Creating the File

cat << 'EOF' > input.txt
error: disk full
warning: cpu high
info: backup completed
error: memory leak
warning: network unstable
EOF

Command to Run

grep -E 'error|warning' input.txt

Output

error: disk full
warning: cpu high
error: memory leak
warning: network unstable

Command to Run

egrep 'error|warning' input.txt

Output

error: disk full
warning: cpu high
error: memory leak
warning: network unstable

How It Works

Method	Description	Notes
grep -E	Enables extended regular expressions	Currently the recommended approach
egrep	Shorthand for grep -E	May be deprecated in some modern environments
error|warning	Search for multiple patterns with OR condition

Explanation

grep -E leverages extended regular expressions to search for multiple patterns concisely.
egrep offers equivalent functionality, but grep -E is now the more common choice.

How to Perform Exact Match Searches Using Multiple Patterns with grep

Creating the File

cat << 'EOF' > input.txt
apple
banana
orange
grape
melon
EOF

Creating the File

cat << 'EOF' > patterns.txt
apple
orange
melon
EOF

Command to Run

grep -x -E 'apple|orange|melon' input.txt

Output

apple
orange
melon

Command to Run

grep -x -f patterns.txt input.txt

Output

apple
orange
melon

How It Works

Option	Description
-x	Perform exact match search on the entire line
-E	Use extended regular expressions
apple|orange|melon	Specify multiple patterns with OR condition
-f patterns.txt	Load patterns from a file

Explanation

Using grep -x allows you to perform exact match searches rather than partial matches.

When there are many search patterns, using patterns.txt makes them easier to manage.

How to Match Only Whole Words Using Multiple Patterns with grep

Creating the File

cat << 'EOF' > input.txt
apple
pineapple
banana
orange
apple pie
banana split
grape
EOF

Command to Run

grep -Ew 'apple|banana' input.txt

Output

apple
banana
apple pie
banana split

Command to Run

grep -E 'apple|banana' input.txt

Output

apple
pineapple
banana
apple pie
banana split

How It Works

Option	Description	Behavior
-E	Use extended regular expressions	Enables OR conditions like apple|banana
-w	Match whole words only	Treats surrounding characters as word boundaries
apple|banana	Specify multiple patterns	Matches apple or banana

Explanation

Using grep -Ew lets you search for multiple patterns with OR conditions while matching only whole words.
This is useful when you want to exclude partial matches like pineapple.

How to Search by Specifying Start-of-Line and End-of-Line Using Multiple Patterns with grep

Creating the File

cat << 'EOF' > input.txt
ERROR: failed to connect
INFO: retry started
ERROR: timeout detected
DEBUG: cache cleared
INFO: process completed
WARNING: disk usage high
EOF

Command to Run

grep -E '^(ERROR|INFO)|high$' input.txt

Output

ERROR: failed to connect
INFO: retry started
ERROR: timeout detected
INFO: process completed
WARNING: disk usage high

How It Works

Item	Description
-E	Enable extended regular expressions
^	Match start of line
$	Match end of line
(ERROR|INFO)	Specify multiple patterns with OR condition
high$	Search for lines ending with "high"

Explanation

Using grep -E allows you to specify multiple patterns concisely.
Combining ^ and $ enables flexible searches conditioned on the start or end of a line.

How to Search Without Case Distinction Using Multiple Patterns with grep

Creating the File

cat << 'EOF' > input.txt
Hello World
hello grep
HELLO LINUX
Error Message
warning message
EOF

Command to Run

grep -Ei 'hello|error' input.txt

Output

Hello World
hello grep
HELLO LINUX
Error Message

How It Works

Item	Description
grep	Command for text searching
-E	Enable extended regular expressions, allowing OR conditions without escaping |
-i	Search without distinguishing uppercase and lowercase
hello|error	Multiple patterns matching hello or error
input.txt	Target file for search

Explanation

Using -E allows multiple patterns to be written simply.
Combining with -i enables flexible searches regardless of uppercase or lowercase.

How to Perform AND Searches Using Multiple Patterns with grep

Creating the File

cat << 'EOF' > input.txt
apple orange banana
apple grape
orange lemon
apple orange
banana grape
EOF

Command to Run

grep 'apple' input.txt | grep 'orange'

Output

apple orange banana
apple orange

How It Works

Mechanism	Description
First grep	Extracts lines containing "apple"
Pipe |	Passes the result of the previous command to the next command
Second grep	Further extracts only lines containing "orange"
AND search	Displays only lines matching both conditions

Explanation

grep can achieve AND searches for multiple conditions by chaining with pipes.
This approach allows step-by-step filtering with multiple keywords and is commonly used in log analysis.

How to Combine NOT Searches Using Multiple Patterns with grep

Creating the File

cat << 'EOF' > input.txt
error: database connection failed
info: retry connection
warning: disk usage high
error: timeout occurred
debug: cache initialized
fatal: unexpected shutdown
EOF

Command to Run

grep -Ev 'error|warning' input.txt

Output

info: retry connection
debug: cache initialized
fatal: unexpected shutdown

Command to Run

grep -v 'error' input.txt | grep -v 'warning'

Output

info: retry connection
debug: cache initialized
fatal: unexpected shutdown

How It Works

Mechanism	Example Command	Description
Specify multiple NOT conditions at once	grep -Ev 'error|warning' input.txt	Use extended regular expressions to exclude lines containing error or warning
Chain NOT conditions	grep -v 'error' | grep -v 'warning'	Chain grep -v with pipes to exclude step by step

Explanation

grep -v is the option for NOT searches.
When handling multiple conditions, combining -E with | is the simplest and most practical approach.

How to Load Patterns from a File Using the -f Option with grep

Creating the File

cat << 'EOF' > patterns.txt
error
warning
failed
EOF

Creating the File

cat << 'EOF' > input.txt
[INFO] process started
[WARNING] disk usage high
[ERROR] connection failed
[SUCCESS] backup completed
failed to connect database
EOF

Command to Run

grep -i -f patterns.txt input.txt

Output

[WARNING] disk usage high
[ERROR] connection failed
failed to connect database

How It Works

Item	Description
-f patterns.txt	Load search patterns from a file
-i	Search without distinguishing uppercase and lowercase
patterns.txt	Define multiple search keywords one per line
input.txt	Target file for search
Behavior	Extract lines matching any of the patterns in patterns.txt

Explanation

Using grep -f makes multiple patterns easier to manage and is convenient for large-scale keyword searches.
Externalizing patterns into a file also improves maintainability and reusability.

How to Search Multiple Files Simultaneously Using Multiple Patterns with grep

Creating the File

cat << 'EOF' > sample1.txt
ERROR: Disk full
INFO: Service started
WARNING: CPU usage high
ERROR: Connection timeout
EOF

Creating the File

cat << 'EOF' > sample2.txt
INFO: Backup completed
WARNING: Memory usage high
ERROR: Failed login attempt
INFO: System shutdown
EOF

Command to Run

grep -E 'ERROR|WARNING' sample1.txt sample2.txt

Output

sample1.txt:ERROR: Disk full
sample1.txt:WARNING: CPU usage high
sample1.txt:ERROR: Connection timeout
sample2.txt:WARNING: Memory usage high
sample2.txt:ERROR: Failed login attempt

Command to Run

grep -e 'ERROR' -e 'WARNING' sample1.txt sample2.txt

Output

sample1.txt:ERROR: Disk full
sample1.txt:WARNING: CPU usage high
sample1.txt:ERROR: Connection timeout
sample2.txt:WARNING: Memory usage high
sample2.txt:ERROR: Failed login attempt

How It Works

Method	Description	Notes
grep -E 'ERROR|WARNING'	Specify multiple patterns with extended regular expressions	Uses | for OR conditions
grep -e 'ERROR' -e 'WARNING'	Specify multiple -e flags	Easy to add more patterns
Specify multiple files	sample1.txt sample2.txt	Can be searched simultaneously
Output format	filename:matched line	Shows which file the match was found in

Explanation

grep can execute multiple pattern searches and multiple file searches simultaneously.
This is an extremely useful approach for log analysis and error investigation.

How to Recursively Search Directories Using Multiple Patterns with grep

Creating the File

mkdir -p project/src

Creating the File

cat << 'EOF' > project/app.log
INFO: Application started
ERROR: Database connection failed
WARN: Retry processing
EOF

Creating the File

cat << 'EOF' > project/error.log
FATAL: System crash
ERROR: Memory leak detected
EOF

Creating the File

cat << 'EOF' > project/src/main.txt
INFO: User login success
DEBUG: Session created
EOF

Creating the File

cat << 'EOF' > project/src/debug.txt
TRACE: API request
WARN: Slow response detected
EOF

Command to Run

grep -r -E "ERROR|WARN" project

Output

project/src/debug.txt:WARN: Slow response detected
project/app.log:ERROR: Database connection failed
project/app.log:WARN: Retry processing
project/error.log:ERROR: Memory leak detected

Command to Run

grep -r -e "ERROR" -e "WARN" project

Output

project/src/debug.txt:WARN: Slow response detected
project/app.log:ERROR: Database connection failed
project/app.log:WARN: Retry processing
project/error.log:ERROR: Memory leak detected

How It Works

Option	Role
grep	Text search command
-r	Recursively search directories
-E	Enable extended regular expressions
"ERROR|WARN"	Search for multiple patterns with OR condition
-e	Specify multiple search patterns
project	Target directory for search

Explanation

With grep, using -E allows OR-condition searches across multiple patterns.
The approach of specifying multiple -e flags is also easy to extend with additional patterns and offers high readability.

How to Exclude Target Directories When Searching Using Multiple Patterns with grep

Creating the File

mkdir -p project/src

Creating the File

cat << 'EOF' > project/app.log
INFO: Application started
ERROR: Database connection failed
WARN: Retry processing
EOF

Creating the File

cat << 'EOF' > project/error.log
FATAL: System crash
ERROR: Memory leak detected
EOF

Creating the File

cat << 'EOF' > project/src/main.txt
INFO: User login success
DEBUG: Session created
EOF

Creating the File

cat << 'EOF' > project/src/debug.txt
TRACE: API request
WARN: Slow response detected
EOF

Command to Run

grep -r -E "ERROR|WARN" --exclude-dir="project/src" project

Output

project/app.log:ERROR: Database connection failed
project/app.log:WARN: Retry processing
project/error.log:ERROR: Memory leak detected

Command to Run

grep -r -E "ERROR|WARN" project

Output

project/app.log:ERROR: Database connection failed
project/app.log:WARN: Retry processing
project/error.log:ERROR: Memory leak detected
project/src/debug.txt:WARN: Slow response detected

How It Works

Option	Description
-r	Recursively search directories
-E	Use extended regular expressions
"ERROR|WARN"	Search for lines matching ERROR or WARN
--exclude-dir="project/src"	Exclude the project/src directory from the search

Explanation

The grep command can search for multiple patterns with OR conditions using -E.
Also, using the --exclude-dir option lets you exclude specific directories from the search.
Excluding unnecessary directories during log searches helps improve search speed and reduce noise.

How to Integrate grep Multiple Patterns with the find Command

Creating the File

cat << 'EOF' > input.txt
logs/app.log:ERROR Database connection failed
logs/app.log:INFO User login success
logs/system.log:WARNING Disk usage high
logs/system.log:ERROR Memory leak detected
backup/data.txt:INFO Backup completed
backup/data.txt:ERROR Backup failed
EOF

Creating the File

mkdir -p logs backup

Creating the File

cp input.txt logs/app.log

Creating the File

cp input.txt logs/system.log

Creating the File

cp input.txt backup/data.txt

Command to Run

find logs backup -type f | xargs grep -E 'ERROR|WARNING'

Output

logs/app.log:logs/app.log:ERROR Database connection failed
logs/app.log:logs/system.log:WARNING Disk usage high
logs/app.log:logs/system.log:ERROR Memory leak detected
logs/app.log:backup/data.txt:ERROR Backup failed
logs/system.log:logs/app.log:ERROR Database connection failed
logs/system.log:logs/system.log:WARNING Disk usage high
logs/system.log:logs/system.log:ERROR Memory leak detected
logs/system.log:backup/data.txt:ERROR Backup failed
backup/data.txt:logs/app.log:ERROR Database connection failed
backup/data.txt:logs/system.log:WARNING Disk usage high
backup/data.txt:logs/system.log:ERROR Memory leak detected
backup/data.txt:backup/data.txt:ERROR Backup failed

How It Works

Command	Role
find logs backup -type f	Find files under logs and backup directories
xargs grep -E 'ERROR|WARNING'	Run grep search with multiple patterns in OR condition
-E	Enable extended regular expressions
ERROR|WARNING	Match ERROR or WARNING

Explanation

By limiting the target directories with find, you can efficiently run grep searches while avoiding unnecessary file scanning.
Using grep -E allows multiple keywords to be searched together with OR conditions.

How to Streamline Log Analysis Using Multiple Patterns with grep

Creating the File

cat << 'EOF' > input.txt
2026-05-20 10:00:01 INFO User login success
2026-05-20 10:01:15 ERROR Database connection failed
2026-05-20 10:02:30 WARN Disk usage above 80%
2026-05-20 10:03:45 INFO Scheduled backup completed
2026-05-20 10:04:50 ERROR Timeout while calling API
2026-05-20 10:05:20 WARN Memory usage high
EOF

Command to Run

grep -E 'ERROR|WARN' input.txt

Output

2026-05-20 10:01:15 ERROR Database connection failed
2026-05-20 10:02:30 WARN Disk usage above 80%
2026-05-20 10:04:50 ERROR Timeout while calling API
2026-05-20 10:05:20 WARN Memory usage high

Command to Run

grep -e 'ERROR' -e 'WARN' input.txt

Output

2026-05-20 10:01:15 ERROR Database connection failed
2026-05-20 10:02:30 WARN Disk usage above 80%
2026-05-20 10:04:50 ERROR Timeout while calling API
2026-05-20 10:05:20 WARN Memory usage high

How It Works

Method	Example Command	How It Works
-E option	grep -E 'ERROR|WARN' input.txt	Use extended regular expressions with | to specify multiple conditions
-e option	grep -e 'ERROR' -e 'WARN' input.txt	Specify multiple conditions by using multiple -e flags

Explanation

Using multiple patterns with grep allows you to extract multiple conditions from large logs all at once.
This is extremely effective for streamlining failure analysis and monitoring log review.

Common Errors and Solutions When Using Multiple Patterns with grep

Creating the File

cat << 'EOF' > input.txt
error: failed login
warning: disk usage high
info: backup completed
error: timeout detected
warning: memory leak suspected
EOF

Command to Run

grep -E 'error|warning' input.txt

Output

error: failed login
warning: disk usage high
error: timeout detected
warning: memory leak suspected

Command to Run

grep 'error|warning' input.txt

Output

(no output)

Command to Run

grep -e 'error' -e 'warning' input.txt

Output

error: failed login
warning: disk usage high
error: timeout detected
warning: memory leak suspected

How It Works

Mechanism	Description
grep -E 'error|warning'	Enable extended regular expressions and perform OR search using |
grep 'error|warning'	| is not interpreted as OR in standard grep
grep -e 'error' -e 'warning'	Achieve OR search by specifying multiple -e flags

Explanation

One of the most common mistakes with grep's multiple patterns is forgetting -E when using |.
If you want to ensure reliable behavior, using multiple grep -e flags is also a widely used approach.

Summary of Key Tips for Efficient grep Multiple Pattern Searches

Understanding grep's multiple pattern search allows you to flexibly handle OR searches, AND searches, and exclusion searches.

Furthermore, combining with the find command and recursive search makes large-scale log analysis and configuration review more efficient.

Start by trying the basic pattern specifications, and learn to choose the right options for each use case.