LINUX COMMAND OF THE DAY

1. grep (Global Regular Expression Print):

Used to search text or patterns inside files.

Syntax:

grep [options] "pattern" filename

Common options:

• -i → ignore case
• -n → show line numbers
• -r → search recursively in directories
• -v → invert match (show lines that don’t match)
• -c → count matching lines

Examples:

grep "hello" file.txt        # Find lines containing "hello"
grep -i "hello" file.txt     # Case-insensitive search
grep -n "main" program.c     # Show line numbers with matches
grep -r "error" /var/log/    # Search for "error" in all files recursively
grep -v "test" file.txt      # Show all lines except those with "test"

2. find

Used to search for files and directories in a directory hierarchy.

Syntax:

find [path] [options] [expression]

Common options:

• -name → search by filename
• -iname → case-insensitive name search
• -type → search by type (f for file, d for directory)
• -size → search by size
• -mtime → search by modification time

Examples:

find /home -name "*.txt"      # Find all .txt files in /home
find . -iname "file.txt"      # Find file.txt (ignore case) in current dir
find / -type d -name "logs"   # Find directories named "logs"
find . -type f -size +10M     # Find files larger than 10 MB
find . -mtime -2              # Find files modified in the last 2 days

3. wc (Word Count)

Used to count lines, words, and characters in a file.

Syntax:

wc [options] filename

Common options:

• -l → count lines
• -w → count words
• -c → count bytes (characters)
• -m → count characters (multi-byte safe)

Examples:

wc file.txt           # Show lines, words, characters
wc -l file.txt        # Count only lines
wc -w file.txt        # Count only words
wc -c file.txt        # Count only bytes
wc -m file.txt        # Count only characters
cat file.txt | wc -l  # Count lines using pipe

Quick summary:

• grep → Search inside file contents
• find → Search for files/directories
• wc → Count lines, words, characters