whatis Command

whatis [OPTIONS] name...

# Get description of a single command whatis ls # Output: ls (1) - list directory contents whatis grep # Output: grep (1) - print lines matching a pattern whatis man # Output: man (1) - an interface to the on-line reference manuals # Multiple commands at once whatis ls grep awk sed

# Example output breakdown whatis printf # Output: printf (1) - format and print data # printf (3) - formatted output conversion # Format: command (section) - description # Section numbers: # 1 - User commands # 2 - System calls # 3 - Library functions # 4 - Device files # 5 - File formats # 6 - Games # 7 - Miscellaneous # 8 - System administration

# File operations whatis cp mv rm mkdir rmdir # Text processing whatis cat head tail sort uniq # System information whatis ps top htop free df du # Network tools whatis ping wget curl ssh scp # Archive tools whatis tar gzip gunzip zip unzip

# Use wildcards to find commands whatis -w "*zip*" # Finds: gzip, gunzip, zip, unzip, etc. whatis -w "ssh*" # Finds: ssh, sshd, ssh-keygen, etc. # Regular expressions whatis -r "^ls" # Finds commands starting with "ls" whatis -r ".*grep.*" # Finds commands containing "grep" # Case-insensitive search whatis -w "*GREP*" # May not find anything whatis -w "*grep*" # Better approach

# Search only in user commands (section 1) whatis -s 1 printf # Search only in library functions (section 3) whatis -s 3 printf # Search in system administration (section 8) whatis -s 8 mount # Search in multiple sections whatis -s 1,8 mount # Compare different sections whatis -s 1 crontab # User command whatis -s 5 crontab # File format

# Use custom manual path whatis -M /usr/local/man:/opt/man ls # Set locale for international manual pages whatis -L fr_FR ls # French manual pages whatis -L de_DE ls # German manual pages # Use custom configuration whatis -C /etc/man_db.conf ls # Debug manual page search whatis -d ls # Verbose output whatis -v nonexistent_command

# Discover text processing tools whatis awk sed grep cut sort uniq tr # Network diagnostic tools whatis ping traceroute netstat ss nmap # System monitoring tools whatis top htop iotop iftop vmstat iostat # File compression tools whatis gzip bzip2 xz tar zip 7z # Find tools for specific tasks whatis -w "*crypt*" # Encryption tools whatis -w "*net*" # Network tools whatis -w "*time*" # Time-related tools

# Quick reminder of command purpose whatis rsync # Output: rsync (1) - a fast, versatile, remote (and local) file-copying tool whatis find # Output: find (1) - search for files and directories whatis chmod # Output: chmod (1) - change file mode bits # Check if command exists and get description whatis docker 2>/dev/null || echo "Docker not installed" # Batch check multiple tools for cmd in git vim emacs nano; do echo -n "$cmd: " whatis $cmd 2>/dev/null || echo "not found" done

#!/bin/bash # Generate command reference for common tools echo "=== System Command Reference ===" echo "Generated on: $(date)" echo categories=( "File Operations:cp mv rm mkdir rmdir ls" "Text Processing:grep sed awk cut sort uniq" "System Info:ps top free df du uptime" "Network:ping wget curl ssh scp" "Archives:tar gzip zip unzip" ) for category in "${categories[@]}"; do title="${category%%:*}" commands="${category##*:}" echo "## $title" echo for cmd in ${commands//,/ }; do desc=$(whatis $cmd 2>/dev/null | head -1) if [ -n "$desc" ]; then echo "- $desc" fi done echo done

# whatis - exact command lookup whatis ls # Output: ls (1) - list directory contents # apropos - keyword search apropos "list directory" # Output: ls (1) - list directory contents # dir (1) - list directory contents # vdir (1) - list directory contents # whatis - specific command whatis copy # Output: copy: nothing appropriate # apropos - find copy-related commands apropos copy # Output: cp (1) - copy files or directories # scp (1) - secure copy (remote file copy program) # rsync (1) - a fast, versatile, remote (and local) file-copying tool # Combined usage apropos network | head -5 # Find network commands whatis ping wget curl # Get specific descriptions

# Update manual page database sudo mandb # Update database for specific path sudo mandb /usr/local/man # Check database status mandb --test # Rebuild database completely sudo mandb --create # Check database locations manpath echo $MANPATH

# Check if command has manual page man -w ls # Show manual page location # Verify whatis database whatis -d ls # Debug output # Check for missing descriptions whatis nonexistent 2>&1 # Force database update sudo mandb --quiet # Check database files ls -la /var/cache/man/ find /var/cache/man -name "whatis*"

# Add custom manual page location export MANPATH="/usr/local/man:$MANPATH" # Update database for custom location sudo mandb /usr/local/man # Test custom manual page whatis custom_command # Create simple manual page # /usr/local/man/man1/mycmd.1 sudo mkdir -p /usr/local/man/man1 sudo tee /usr/local/man/man1/mycmd.1 << 'EOF' .TH MYCMD 1 "January 2025" "1.0" "User Commands" .SH NAME mycmd \- my custom command .SH DESCRIPTION This is my custom command description. EOF # Update database and test sudo mandb /usr/local/man whatis mycmd

#!/bin/bash # Check if commands are available and documented check_command() { local cmd="$1" if command -v "$cmd" >/dev/null 2>&1; then local desc=$(whatis "$cmd" 2>/dev/null | head -1) if [ -n "$desc" ]; then echo "✓ $cmd: $desc" else echo "? $cmd: installed but no manual page" fi else echo "✗ $cmd: not installed" fi } # Check required commands REQUIRED_COMMANDS="git vim curl wget ssh" echo "Checking required commands:" for cmd in $REQUIRED_COMMANDS; do check_command "$cmd" done

#!/bin/bash # Generate command cheat sheet generate_cheatsheet() { local category="$1" shift local commands=("$@") echo "## $category" echo for cmd in "${commands[@]}"; do local desc=$(whatis "$cmd" 2>/dev/null | head -1 | cut -d' ' -f3-) if [ -n "$desc" ]; then echo "**$cmd** - $desc" echo fi done } echo "# Linux Command Reference" echo generate_cheatsheet "File Operations" cp mv rm ls mkdir generate_cheatsheet "Text Processing" grep sed awk cut sort generate_cheatsheet "System Monitoring" ps top free df du generate_cheatsheet "Network Tools" ping wget curl ssh

#!/bin/bash # Interactive command discovery tool explore_commands() { echo "Command Explorer - Enter keywords to find related commands" echo "Type 'quit' to exit" echo while true; do read -p "Search keyword: " keyword case "$keyword" in quit|exit|q) echo "Goodbye!" break ;; "") continue ;; *) echo echo "Commands matching '$keyword':" apropos "$keyword" 2>/dev/null | head -10 echo echo "Or try exact match:" whatis "$keyword" 2>/dev/null || echo "No exact match found" echo ;; esac done } explore_commands

# Check if whatis is working whatis whatis # Check manual database location manpath # Check database files find /var/cache/man -name "*whatis*" -ls # Test with known command whatis ls || echo "Database issue" # Check manual page exists man -w ls # Debug whatis search whatis -d -v ls # Check system locale locale echo $LANG

# Rebuild manual database sudo mandb --create # Update specific manual paths sudo mandb /usr/share/man /usr/local/man # Fix permissions sudo chown -R man:man /var/cache/man sudo chmod -R 755 /var/cache/man # Clear and rebuild cache sudo rm -rf /var/cache/man/* sudo mandb # Install missing manual pages sudo apt install man-db manpages manpages-dev # Debian/Ubuntu sudo yum install man-db man-pages # RHEL/CentOS