Linux Workshop

Helpful Command Line Utilities

July 27, 2005

Quick Special Symbols Primer

• ~ - expands to your home directory (Example: cd ~)
• . - expands to the current directory (Example: ls .)
• .. - expands to the parent directory (Example: ls ..)

Getting Help

• help - bash command-line/scripting help
• apropos - use this if you're looking for a command that does <insert task here> (Example: apropos edit)
• man - looks up help files for various commands (Example: man grep)
• info - opens an emacs-like interface for extensive guides to commands (Example: info make)
• whatis - shows a quick overview of the command (Example: whatis ls)

Nifty Bash Commands

• pushd and popd - quick directory traversal
  
  • Example:
    cd ~
pushd /usr/share/doc
pushd
popd
  • You can also cd - to change to the directory you were just in.
• alias - command aliasing
  
  • Example:
    alias -p
alias changecd="eject; sleep 5; eject -t"
changecd
• control-r - reverse search
• ~/.bashrc can be used to automatically add aliases

Nifty File Manipulation Tools

• grep - string searching in files
  • lots of different options (Use grep --help or man grep to see them all)
  • ways of calling grep: grep, egrep, rgrep
  • Examples:
    • grep -v apple fruits.txt
    • egrep '.*berry.*' fruits.txt
    • rgrep a * (recursive search)
• wc - count the number of letters, words, and paragraphs in a file
• cat - print out a file's contents
• sort - sort a file alphabetically or numerically (Example: sort -r vegetables.txt)
• tail - print the last few lines of a file
• head - print the first few lines of a file
• uniq - remove (sequential) duplicate lines in a file (Example: uniq names.txt)
  • You can use sort and uniq together to quickly tidy up files.
  • Example: sort names.txt | uniq (see Piping below)
• sed - regular expression/scripting tool
  • Regular expressions are a way to flexibly match/replace text.
  • Example: sed -r -e 's/tomato/squash/' vegetables.txt (replaces all occurrances of "tomato" with "squash")
• Handy console text editors:
  • vim
  • emacs
  • nano

Nifty File Searching Tools

• ls - list directory contents
• find - a tool for recursive directory searching
  • Many options, check out man find or find --help to see them all.
  • Example: find . -iname '*.log' (will list all files/directories contained in the current directory (".") that match the pattern "*.log" (case-insensitive))
• locate - a simple tool for finding files system-wide
  • Note: you may need to run updatedb (as root) first before you use locate (especially if you're searching for a new file), but many Linux systems automatically run this command on a daily basis.
  • Example: locate apache
• whereis - shows the full directory path to a command you're looking for (Example: whereis bash)

Nifty Commands Related to Processes and Running Applications

• ps - view running processes
  • Run with no options, ps shows the user's processes.
  • To show all processes, type something like this: ps -ax
• pstree - view running processes in a tree format
• killall - kill errant processes (use with caution!) (Example: killall kwrite)
• nice - run a process at a different priority level
  • Use nice if you want a costly program to use up less of your system resources.
  • You can also use nice to boost the priority of a process (see man nice)
  • Example: nice find / -name '*'
• lsof - show which files processes are using (helpful for umounting)

Nifty Disk Usage Utilities

• df - show disk usage on all mounted drives (Example: df -h)
• du - show disk usage in a specified directory (Example: du . -sh)
• mount - mount a device to a directory (see man mount for complete instructions)
  • Can mount devices such as the CD-ROM drive, USB memory stick, or iPod to a specified directory.
  • Type mount with no arguments to see what devices are mounted.
  • Run umount to unmount a drive.

Nifty Printing Utilities

• lpstat - show information about printers (Example: lpstat -p)
• lpr - print files from the command line (Example: lpr -P laser1 fruits.txt)

Other Nifty Commands

• lynx - console web browser
• bc - math interpreter (Example: echo 5*6/3+23 | bc)
• cal - calendar (Example: cal -3)

Commands Just For Fun

• fortune - random quotes and witty sayings (install by running apt-get install fortune as root)
  • Example quotes from fortune:
    • Abandon the search for Truth; settle for a good fantasy.
    • Celebrate Hannibal Day this year. Take an elephant to lunch.
  • Install the "fortunes" package for extra fortunes (run apt-get install fortunes as root)
    • Examples:
      • fortune startrek - "Live long and prosper." -- Spock, "Amok Time", stardate 3372.7
      • fortune linux - "Why use Windows when you can have air conditioning? Why use Windows, when you can leave through the door?" -- Konrad Blum
• scrabble - a text-based scrabble game (installation: apt-get install scrabble)
• adventure - a text-based roleplaying game (installation: apt-get install bsdgames)

Piping and Redirecting Output

• Many commands that run in the console can redirect their output to a file or another program using special characters.
• Redirecting output
  • >, >>, and &>
    • > will truncate any file that you specify before outputting.
    • >> will append output to a file.
    • &> will truncate and send both normal and error messages to a file.
  • Make sure you don't use > when you mean >>!
  • Examples:
    • sort names.txt > sorted-names.txt
    • cat vegetables.txt >> fruits.txt
    • grep &> grep-error.txt
• Piping
  • Use the | symbol to pipe output.
  • Examples:
    • sort names.txt | uniq
    • sort vegetables.txt | egrep '^c' | wc

Other resources

• Command Line Essentials
• Command Line Tutorials