Filter

Grep

grep -orIinm1 --color=always --exclude-dir=".git" "replace_me" ./ | cut -c1-1000 && tput sgr0  # Search recursively for "replace_me" and show first 1000 chars

less -I +5 +/replace_me file.txt     # Open file.txt in less, ignore case, jump to line 5, highlight "replace_me"
less -I +5 file.txt                  # Open file.txt in less, ignore case, start at line 5
nvim +5 file.txt                     # Open file.txt in nvim starting at line 5

Pipes

ls | wc -l                                      # Count number of files in current directory
ls | grep host                                  # List files containing "host"
tail -20 /var/log/messages | grep -i vagrant    # Show last 20 log lines containing "vagrant"
free -m | grep Mem                              # Show memory info
ls -l | head                                    # Show first lines of detailed file listing

File Operations

Viewing Files

less example.txt                     # View example.txt with pagination
more example.txt                     # Alternative pager to view example.txt
head -10 example.txt                 # Show first 10 lines of example.txt
tail -10 example.txt                 # Show last 10 lines of example.txt
tail -f /var/log/messages            # Monitor system log messages in real time

Compare files

diff [file1] [file2]

Count (lines, words, and characters)

wc <file>      # Count lines, words, bytes
wc -l <file>   # Prints the number of lines in file
wc -w <file>   # Prints the number of words in file
wc -m <file>   # Prints the number of characters in file

Find

Search files with find

find <path> -type <type> -name <pattern>  # Search files starting from [path] matching [pattern]

Example:

find . -name "*.log"  # Starting from current directory, search all subdirectories for files ending with '.log'

Excluding a directory:

find . -path "./.git" -prune -o -name "*.txt" -print  # Find all .txt files excluding .git directory

Locate vs Find

find /etc -name 'host*'              # Find files in /etc starting with "host"
updatedb                             # Update file location database
locate host                          # Locate files named "host"

Extra Commands

Grep Filtering

grep -i firewall example.txt         # Search for "firewall" (case-insensitive) in example.txt
grep -i firewall < example.txt       # Alternative input method for the same search
grep -i firewall *                   # Search for "firewall" in all files in current directory
grep -iR firewall *                  # Search recursively for "firewall" in all files
grep -R SELINUX /etc/*               # Search recursively for "SELINUX" in /etc
grep -vi firewall example.txt        # Show lines that do NOT contain "firewall"

Text Processing

cut -d: -f1 /etc/passwd              # Extract first field (username) from /etc/passwd using ':' as separator
awk -F':' '{print $1}' /etc/passwd   # Same as above using awk
sed -i 's/word/new_word/g' *.txt     # Replace 'word' with 'new_word' in all .txt files