Chapter 3: Command Line Utilities

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Chapter 3Command Line Utilities

• Doin stuff

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In this chapter

• Special characters
• Redirection
• More utilities than you shake a stick at

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Typing Commands

• Beware of special characters
• Characters that have special meaning to the shell
• Shell expands, modifies and interprets special
  characters before issuing the command

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Special Characters

• ? ( ) lt gt / \ !
• Plus whitespace (tabs, spaces, newlines)
• Do not use these in filenames unless you have to
• To use them, either put in single quotes, or
  proceed with a backslash
• ls filename with special chars!!
• ls \cat\

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Special Characters cont

• All special characters have special meaning to
  the shell
• Well explore these in great detail in upcoming
  chapters

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Utilities

• Linux Unix come with thousands of utilities
• Some used explicitly, others implicitly
• Some text-based, some GUI, some both

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Some tips before we start

• Tab completion
• When typing a filename or command name, you can
  type the first few letters then hit TAB to
  auto-complete the command
• Pipe () symbol
• Used to chain commands together
• The output of one command becomes the input of
  another
• Well revisit this in detail later

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ls LiSt files

• Used to list files contained in a directory
• Can narrow the search using pattern matching
• Examples
• ls ? displays all the files in the directory
• ls cats ? displays the file cats in the directory
• ls ca ? displays files starting with ca

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cat catenate a file

• Displays the contents of one or more files
• Beware dont try with binary files
• Examples
• cat myfile ? displays contents of myfile
• cat file1 file2 ? displays contents of file1
  followed by contents of file2

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rm ReMoves a file

• Similar to del in DOS
• Use the i option to invoke interactive mode,
  which prompts you if youre sure
• Examples
• rm myfile ? deletes myfile
• rm i myfile ? prompts you before deleting

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more and less pagers

• more and less are similar in that they both break
  up long files into page long chunks
• Press h to display possible commands
• Examples
• less myfile ? displays myfile one page at a time

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hostname Where am I?

• hostname will display the name of the system you
  are currently logged onto
• Usually a fully qualified domain name (FQDN)
• Example
• hostname ? displays ares.bcs.solano.cc.ca.us

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cp CoPies files

• Usage cp sourcefile destinationfile
• Creates a copy, leaves sourcefile intact
• If destinationfile exists, it will be overwritten
• Unless you use i option
• Example
• cp myfile myfile.backup

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mv MoVe files / change name

• Usage mv existingfile newfile
• Just like cp, can overwrite with i option
• Renames a file, which can also move it to another
  directory
• Examples
• mv myfile foshizzle
• mv /dir1/myfile /dir2/myfile

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lpr Line PRinter

• Places files into the print queue
• Usage lpr -Pprintername files
• You can check the status of queue with lpq
• You can delete a job with lprm
• Sorry, we dont have a printer

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grep global regular expression print

• Used to search for strings in files/output
• Usage grep expression filename
• Returns lines with expression in filename
• Example
• grep automagically myfile

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head display beginning

• Displays beginning of file
• head -X filename displays first X lines
• Check out pg 727/691 for more options

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tail duh

• Displays the end of a file
• tail -X myfile displays the last X lines
• Check out pg 843/783 for more options

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sort displays sorted info

• sort displays data in a sorted manner, without
  altering the original file
• Lots of options sort alphabetically,
  numerically, with or without repeats, reverse
  order, etc
• Check out pg 817/762

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uniq removes duplicates

• uniq displays data, omitting successive repeat
  entries
• Have to sort file first otherwise it might not
  find all duplicates
• Does not alter original file

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file what kind of file is this?

• Usage file filename
• Tells you what kind of file youre working with
  and what kind of data is in it
• Examples include program, shell builtin, ASCII
  text, compressed data, etc

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echo display text

• Displays (echoes) text back to the terminal
  screen
• Can print out contents of shell variables
• Useful in shell scripts
• In other words, seems dumb now but well use it a
  lot down the road

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date displays time and date

• Command options can change formatting
• Privileged accounts can use date to change date
  and time
• Can be useful for scripting

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script captures session

• Captures all input and output on the terminal and
  saves to a file
• A good way to document your work, or capture
  errors for analysis
• Type script to start capture, exit to quit
• By default stores everything in the file
  typescript

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Text Converters

• unix2dos and dos2unix
• Unix and DOS use different end of line characters
• Use these utilities when moving text files back
  and forth between Windows and Linux systems
• Weird script error? Try dos2unix

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Compressing files

• bzip2 files
• gzip files
• compress files
• Each use their own algorithms and have their uses

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Uncompressing files

• bunzip2 compressed-file
• gunzip compressed-file
• ucompress compressed-file

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tar Tape ARchive

• Packs and unpacks files from archives
• Does not compress, only assembles
• Tons of options, allowing you to add or remove
  files from archive, and also apply compression
  using third party support

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which locates utilties

• Will display the location of a utility
• which ls ? displays location of ls command
  youre using
• In case of there being multiple locations, which
  only displays the first (i.e., the one you will
  be using)

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whereis locates utilities

• Similar to which, but displays the utilities in a
  standard set of locations
• The first one listed may not be the one you will
  issue when you enter the command
• All depends on your PATH (chapter 4)

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Sidenote

• which and whereis do not list shell builtins
• Shell builtins are functions that are internal to
  the shell itself no binary executable
• To see if youre using a builtin, use type

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apropos what do I use?

• Not sure what utility youre looking for?
• Try apropos keyword
• Displays utilities and libraries related to your
  keyword
• Found one, but not sure? whatis utility to show
  what it does, or check man page

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locate search for files

• System maintains a database of files
• Your system administrator should configure a job
  to regularly update this database
• Searches for any kind of file not just
  utilities
• Some systems use slocate (secure)
• Latest distros use mlocate via locate

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who Whos online?

• Displays what users are logged on
• Also displays when they logged on, and with what
  device (terminal or console, etc)
• Also try who am i

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finger reach out and touch

• finger by itself displays users logged on like
  who, but also shows idle time and office location
• finger username shows info about that user, like
  home directory, last logon, their shell, if they
  have unread mail, and .plan and .project files

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w Whats up?

• w is similar to who by showing whos logged on
• Also shows system uptime, and memory and CPU load
  averages
• Good overall status of the system

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write send a message

• write username opens up a text-based chat with
  the user
• Type message
• Wait for response
• CTRL-D to exit write

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mesg Enable/disable write

• Usage mesg yn
• Turns off whether users can write you or not
• Useful if you dont want to be bugged

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mail system mail

• Our system is a closed system
• You can send mail to other users on the system
• No public mail