find Command

1
find Command

• Characteristics
• Locate files descending from multiple starting
  points
• Employs regular expressions
• Examples
• On entire system gtfind / -name "cs"
• Two starting points gtfind /usr /var/html name
  "cs"
• Case insensitive gtfind /usr iname "htm"
• More than 3 days ago gtfind /usr -mtime 3 name
  "htm"
• Within the last 3 days gtfind /usr mtime -3
  name "htm"

2
Customizing your prompt

• To set set PS1 variable with a prompt string.
• Additional prompt string capabilities\d
  todays date\H host name\T current time\w
  working directory\! history number of this
  command
• Example export PS1"gt"
• Example export PS1"\! \w gt"

3
Disk Usage Commands

• Free Blocks gtdf
• Disk usage
• Size of each directory (recursive) gtdu
• Summary of each directory (not recursive)gtdu s
  
• Size of a single directory gtdu s ltfileNamegt
• Sort usage, numeric reverse, page at a timegtdu
  sort nr more

4
Managing Processes

• Display processes and pid number
• gtps displays all of your processes
• gtps a removes "only yourself" restriction
• gtps x remove "must have a terminal" restriction
• gtps u display in a user friendly format
• gtps aux combines the above options
• gtps l displays your processes in long format
• Kill a process
• gtkill -9 ltpidgt force terminate the pid specified
  using signal 9

Note the above ps options should not be preceded
with a dash (-)
5
Foreground, Background, Suspend

• Concepts
• A single foreground process can run within the
  shell
• Many background processes can run outside the
  shell
• A suspended process stops running till it is
  restarted
• Commands
• suspend process and move to background ltctrlgtz
• track background processes gtjobs
• resume last suspended process in background gtbg
• resume nth background process gtbg n
• move last suspended process to foreground gtfg
• move nth background process to foreground fg n
• run a command in the background gtsort file

6
Bash Command Processing

• Read a command
• Transform the command
• Process history substitutions
• Process alias substitutions
• Process special character (break sequences)
• Process variable substitutions
• Process command substitutions
• Process pathname expansions
• Execute the Command
• Back to step 1 to get next command

Note transformations occur in the order stated
above
7
Bash History

• Turn on History command export HISTSIZE20
• Clear history list history -c
• History list gthistory
• Execute nth history command gthistory gt!3
• Execute last command gtgrep Bush grades gt!!
  awk 'print 4'
• Use arguments from the last command echo !
• Use last argument of last command gtcp prog.c
  new.c gtls !
• Use the first argument of last command gtls
  l gtecho !
• Navigate around history commands use arrow keys

Note argument is anything following the command
name
8
Aliases
Replace a word by a string when starting a command

• Definition Replace a string by a word at the
  start of a command
• Use Shorten what needs to be typed by aliasing a
  command with its arguments
• Use Rename a command to something more familiar
• Examples
• Display all of the aliases in use gtalias
• Example (dos user directory list) gtalias dir'ls
  l'
• To remove an alias gtunalias dir

9
Creating Script Variables

• create a variable ltvargt"value"
• Note do not use spaces
• Example gtTEAM"Yanks" gtecho TEAM
• Variables are case sensitive
• You can use variables anywhere in
  commnads gtbindirbin gtecho bindir
• To make variables accessible to all sub shells,
  use export gtexport TEAM"yanks"

10
Command Substitution
The output of one command becomes part of another

• Setting variables ltcmdgt or (ltcmdgt)
• Examples
• gtdirpwdgtecho dir
• files(ls)echo files
• echo there are grep ci bush grades bush\'s
• From command line ltcmdgtecho dategrep "abc"
  cat file.txt

Note The back quote is found on the top left of
most keyboards
11
Pathname Expansions

• Any string of 0 or more length
• Any single character ?
• Any single character specified abc
• Examples
• ls cs367/.c
• ls cs367c
• ls newfile???
• ls out12

Notes Filenames must not have an initial period
or slashes
12
Change File Mode (chmod)

• Change permissions of a file
• Examples
• write for user and group, read for worldgtchmod
  ugw,or trak
• all permissions for user, read and execute for
  group and world gtchmod urwx,gorx file.cgi
• Remove execute permission to user, read, and
  world gtchmod a-x fileName

13
File Permissions

• Ls l format -rw-r--r-- 1 owner group 213 Aug
  26 1631 README
• The line contains
• - for a regular file or d for a directory
• permission string (user, group, and other
  (world))
• Number of links to file or directory
• the file size in decimal right-justified in a
  13-byte field
• modification data
• file name
• Permission groups uuser, ggroup, oother
  (world), aall
• Permission types read r (4), write/delete w
  (2), execute x (1)

14
PATH Environment Variable

• Most unix commands are C programs
• When you execute a command
• PATH contains a series of path names
• The shell searches all variables in PATH
• To add program/bin to the PATH variableexport
  PATH PATHprogram/bin
• To add the current directory to PATHexport PATH
  PATH.

15
Shell Scripts
See Bash's Beginners guide See examples on the
class web site

• Put multiple commands in a file and then execute
  them by typing the file name
• They execute the statements one by one
• Creating a script
• The first line should be !/bin/bash
• Other lines starting with are comments
• Make executable ux scriptName
• Execute ./scriptName unless working directory
  is in the search path
• Use script capabilities to
• create loops
• create decisions
• write functions

16
Arguments to a Shell Script

• Arguments to a script
• 0 is the name of the shell script (argument 0)
• 1 is the first argument
• 2 is the second argument
• k is the kth argument
• is the number of arguments
• _at_ is all of the arguments
• Example scriptFile x y z
• 0 scriptFile
• 2 y
• is 3
• _at_ is x y z

17
Shell Script Decisions

• if condition then ltstatementsgt fi
• if condition then ltstatementsgt else fi
• if 1 3
• then
• echo "arg equals 3"
• else
• echo "arg not 3"
• fi

Note space after and before Comparators !
-lt le gt ge f -r where -f is file r for
readable file
18
while and do Loops

• while condition do
• command1 command2 command3
• done
• i0
• while i lt 4 do echo "Welcome i"
  ii1 done
• or
• i0
• do until i 4 do echo "Welcome i"
  ii1 done
• or
• i0
• while i lt 4
• do
• echo "Welcome i"
• ii1
• done

Semicolons separate parts of the loop on the same
line Boolean variables true or false are legal
19
for Loop

• for ltvarNamegt in ltlist of wordsgtdo
  ltstatementsgt done
• Example for i in cat list do cp "i"
  "i.bak" done
• Example for i in PATHNAME/ do rm PATHNAME
  done
• Example gtfor x in do echo x done
• Note the last example is directly from the
  command line

20
Calculate the average in a script

• !/bin/bash
• value0
• count0
• for i in _at_
• do
• valuevaluei
• countcount1
• done
• averagevalue/count
• echo average

21
Script Functions

• ltfuncNamegt() ltcmdListgt
• Example ll ll() ls l more
• ll
• Note Function must be declared before it can be
  used.
• Note Spaces required before and after braces
• Note A common error is forgetting the required
  spaces

22
Functions with arguments

• Arguments
• _at_ means all arguments
• 1 first argument
• 2 second argument
• number of arguments
• Example ll() ls lR _at_ more ll /
• Example mycd() cd _at_ pwd

23
Shell Startups

• For bash, edit /.bash_profile
• In this file, include
• aliases
• variables
• functions
• setting the search path (PATH)
• Good idea
• Make the script in a test file first

Note .bash_profile executes on log in, .bashrc
executes starting sub shells