What are grep, fgrep, egrep?[Pattern Matching Command]

What are grep, fgrep, egrep?

1️⃣ grep – General Pattern Search (Basic Regular Expressions)

1)grep command:-(global regular expression print)

• Uses Basic Regular Expressions (BRE)
• Most commonly used command

Syntax

grep "pattern" file_name

Example

grep "unix" notes.txt
grep "m" a.txt
grep "M" a.txt
grep -i "M"  a.txt  #case insensitive
grep -c "M" a.txt  #line count
grep -n "M" a.txt #line number
grep -w "MM" a.txt # word 

grep -f a.txt b.txt #mathching of two file
grep -L "unix" * #file names that matches & pattern

🔹 Searches lines containing unix

Using regex

grep "^u" notes.txt

🔹 Lines starting with u

2️⃣ fgrep – Fixed String Search (Fast & Simple)

2)fgrep command:-fixed-character strings in a file

• No regular expressions
• Searches exact words or strings
• Faster for plain text

Syntax

fgrep "pattern" file_name

Example

fgrep "unix|linux" notes.txt
fgrep "mm" a.txt
fgrep -c "m" a.txt #line number
fgrep "m" *.txt
fgrep -l "@a" a.txt #print filename
fgrep -n "@a" a.txt #print line number
fgrep -x "a" a.txt   #display only lines matched entirely.

🔹 Searches the exact text unix|linux
(Not OR condition)

✅ Best when:

• You don’t want regex
• You want speed

3️⃣ egrep – Extended Regular Expressions

• Uses Extended Regular Expressions (ERE)
• Supports |, +, ?, ()

Syntax

egrep "pattern" file_name

Example

egrep "unix|linux" notes.txt
egrep "mital"  *    #globally search
egrep "m" a.txt
egrep -c "mm" a.txt   #linenumber mathched
egrep -l "mm" a.txt  # print filename
egrep -n "mm" a.txt # print linenumber
egrep -r "m*" m.txt
egrep -r "m*" .     #recursively searching whole root

🔹 Matches unix OR linux

egrep "(cat|dog)s?" animals.txt

🔹 Matches cat, cats, dog, dogs

🔁 Key Differences (Very Important for Exams)

⚠️ Important Note (Modern UNIX/Linux)

Today:

• fgrep = grep -F
• egrep = grep -E

Examples

grep -F "unix|linux" file.txt
grep -E "unix|linux" file.txt

📝 Easy Memory Trick

• grep → basic search
• fgrep → fixed text (no regex)
• egrep → extra power (OR, +, ?)