Unix Lecture 4

1
Unix Lecture 4

• Hana Filip

2
File Management with Shell Commands

• The verbose listing shows the file permissions of
  a given file
• -rwxr-xr-x
• directories have a "d" in the first column
• regular files have a "-".
• the remaining 9 characters indicate owner, group,
  and world permissions of the file
• An "r" indicates it's readable
• "w" is writable,
• "x" is executable
• A dash in the column instead of a letter means
  that particular permission is turned off.

3
File Management with Shell Commands

• r readable
• w writable
• x executable
• - permission is turned off
• -rwxr-xr-x
• a plain file that is read-write-execute by
  the owner, and read-execute by group and world.
• drwx------
• a directory that is read-write-execute by
  owner, and group and world have no permissions at
  all.

4
File Management with Shell Commands

• chmod permissions file
• Changes the permissions of the named file.
• You can use numbers
• chmod 755 index.html
• The first number translates to permissions by the
  owner. The second is permissions for the group.
• The third is permissions for everyone.
• Number Perms
• 0 --- no permissions
• 1 --x executable only
• 2 -w- writable only
• 3 -wx writable and
  executable
• 4 r--- readable only
• 5 r-x readable and
  executable
• 6 rw- readable and
  writable
• 7 rwx readable, writable,
  and executable

5
File Management with Shell Commands

• A second way of setting permissions is with
  letters
• chmod urwx index.html
• chmod gorx index.html
• u is the owner's ("user's") permissions
• g is the group permissions
• o is "other" or world permissions.
• The sign turns the stated permissions on
• the sign turns them off
• If you want to change a file so that it's group
  writable, but not readable or executable, you'd
  do
• chmod gw,g-rx index.html

6
Example of a simple shell script

• This script displays the date, time,
• username and current directory.
• echo "Date and time is"
• date
• echo "Your username is whoami"
• echo "Your current directory is"
• pwd

7
Example of a simple shell script

• This script displays the date, time,
• username and current directory.
• echo "Date and time is"
• date
• echo "Your username is whoami"
• echo "Your current directory is"
• pwd

8
Example of a simple shell script

• This script displays the date, time,
• username and current directory.
• lines beginning with a hash () are comments and
  are not interpreted by the Shell.

9
Example of a simple shell script

• This script displays the date, time,
• username and current directory.
• echo "Date and time is"
• When used as a Shell command echo echo prints its
  argument
• When echoing multiple words, they must be placed
  within quotes (single or double)

10
Example of a simple shell script

• This script displays the date, time,
• username and current directory.
• echo "Date and time is"
• date
• echo "Your username is whoami"
• The backquotes () around the command whoami
  illustrate the use of COMMAND SUBSTITUTION To
  include the output from one command within the
  command line for another command, enclose the
  command whose output is to be included within
  backquotes.

11
Executing the shell script

• Before using a file as a shell script you must
  change its access permissions so that you have
  execute permission on the file, otherwise the
  error message Permission deniedis displayed.
• To give yourself execute permission for the file
  containing the script use the command
• chmod urwx display
• To run the shell script, simply type its name at
  the prompt. The commands in the script will then
  execute one at a time as though you were typing
  them in at the terminal.

12
Executing the shell script

• chmod u-x display
• display
• display Permission denied.

13
Searching for something in a fileGREP

• The grep family is a collection of three related
  programs for finding patterns in files. Their
  names are grep, fgrep, and egrep.
• The name grep has its origin in the phrase "Get
  Regular Expression and Print
• grep is a full-blown regular-expression matcher
• fgrep "fixed string grep only searches for
  strings
• egrep extended grep

14
Searching for something in a filefgrep

• fgrep the easiest (but not fastest) one to use
• Syntax
• fgrep options 'search string filenames
• Interpretation
• In the name fgrep the f stands for "Fixed
  string", and not "Fast" (contrary to what the man
  page may tell you). The fgrep program finds all
  the lines in a file that contain a certain fixed
  string. So, for example, I could find all
  occurrences of CA in the files in the current
  working directory simply by typing this command
• fgrep CA

15
Searching for something in a filefgrep

• Like many UNIX filters, it can take as many file
  names as you like to supply. And of course it
  permits various adverbs that specify options two
  useful ones are
• -i ignore the difference between upper case and
  lower case when deciding what is a match
• -v reverse the effect of the search by
  outputting only the lines that don't match
• fgrep -i CA
• fgrep -v CA

16
Searching for something in a filefgrep

• The key limitation of fgrep is that you cannot
  use it to get approximate matches, or matches of
  more complicated patterns that cannot be
  described by just giving a fixed string.
  Sometimes you are not quite sure what string you
  are looking for for example, you might know only
  that the word you are seeking begins with z and
  ends with -ic, and had the sequence gm in it
  somewhere. What you need, then, is not a program
  that will find the matching lines for you if you
  give it the exact string you need to find, but
  rather a program that can understand a language
  in which you can say things like "begins with z
  and ends with -ic or -ics and had gm in it
  somewhere."

17
Searching for something in a filegrep

• called up by giving a command that has this form
• grep options pattern description
  files_to_search_in
• grep -i 'pullaeioumn shakespeare
  bad_phone_numbers display
• This means, "without distinguishing between upper
  and lower case, search the files shakespeare
  bad_phone_numbers display for lines that contain
  pull followed by a vowel letter followed by an m
  or an n". Thus it is looking for Pullum, Pullam,
  Pullen, PULLUN, pullum_at_grove.ufl.edu, etc., etc.
• The expression pullaeioumn is a pattern
  description covering the name Pullum and most
  common variants of it. Thus it is looking for
  Pullum, Pullam, Pullen, PULLUN,
  pullum_at_grove.ufl.edu.
• The pattern descriptions used with grep are in a
  language called the language of regular
  expressions. This is one of the most important
  and fruitful developments in modern computer
  science, and in order to use grep you need to
  understand regular expressions thoroughly.

18
Searching for something in a filegrep

• There are various dialects of the regular
  expression language that are used by various UNIX
  programs.
• Here we will be talking about grep and its
  extended cousin egrep. (Read the excellent
  summary with examples in Unix in a Nutshell,
  particularly chapter 6, and do man grep on a
  NetBSD machine to check the details of the GNU
  grep that runs on those machines.
• (GNU pronounced guh-noo, approximately like
  canoe launched in 1984 to develop a complete
  Unix-like operating system which is free
  software, often referred to as LINUX)
• Note that the grep that runs on other machines
  may be a different program, with lots of
  differences in its behavior from the GNU version.

19
Searching for something in a filegrep

• There are various dialects of the regular
  expression language that are used by various UNIX
  programs.
• Here we will be talking about grep and its
  extended cousin egrep. (Read the excellent
  summary with examples in Unix in a Nutshell,
  particularly chapter 6, and do man grep on a
  NetBSD machine to check the details of the GNU
  grep that runs on those machines.
• (GNU pronounced guh-noo, approximately like
  canoe launched in 1984 to develop a complete
  Unix-like operating system which is free
  software, often referred to as LINUX)
• Note that the grep that runs on other machines
  may be a different program, with lots of
  differences in its behavior from the GNU version.

20
Searching for something in a filegrep

• Example The match the phrase that begins
  with z at the beginning of a line and ends in -ic
  or -ics at the end of the line, and it has gm in
  it somewhere, is expressed in the language of
  regular expressions in this form
• z.gm.ics
• To be more precise, what this regular expression
  means is
• "beginning of line followed by z followed by
  optional other material followed by gm followed
  by optional other material followed by -ic
  followed by zero or more occurrences of s
  followed by end of line"
• It can therefore be used in a grep command to
  search for a word in a dictionary where each word
  is on a separate line meeting the description
• grep 'z.gm.ics' dictionary
• Search result zeugmatic

21
Searching for something in a filegrep

• The most trivial case of a regular expression is
  that of a fixed string of the sort that fgrep
  recognizes. Fixed strings are regular
  expressions that are matched only by strings
  identical to themselves.
• The regular expression Z is matched by any
  occurrence of Z. There happens to be only one
  line in The Great God Pan (/class/lin6932/c6932aab
  /machen.txt) that matches it, namely the middle
  line of these three
• remained. These three, however, were 'good
  lives,' but yet
• not proof against the Zulu assegais and typhoid
  fever, and so
• one morning Aubernoun woke up and found himself
  Lord
• Because the middle line matches the expression Z,
  you can fetch (a copy of) that line out of the
  file like this
• grep Z machen.txt
• not proof against the Zulu assegais and typhoid
  fever, and so

22
Searching for something in a filegrep

• fgrep Z machen.txt
• fgrep would do the same thing.
• But what fgrep cannot do is to call for all lines
  with Au possibly followed by some other
  lower-case letters and then an n. That is
  accomplished by the regular expression
• Aua-zn
• this RE is matched by any sequence of a capital A
  followed by a lower-case u followed by zero or
  more letters in the range lower-case a to
  lower-case z followed by lower-case n. This means
  it will be matched by any string containing a
  word like word like any of these Aubernoun,
  Augustine, Austin, etc.

23
Searching for something in a filegrep

• fmt -1 machen.txt tr -d 'punct ' grep
  'Aua-zn' sort -u
• The fmt command is to break the words up and put
  them one on each line
• the tr -d 'punct' command erases all
  punctuation, and spaces
• the sort -u command sorts the search result
  alphabetically

24
Searching for something in a filegrep

• grep 'Aua-zn' machen.txt
• Aus t r a l a b r a c a d a b r a l a l i o l a
  s i an
• Au a-z n

25
Searching for something in a filegrep

• Example
• The zipcodes in the near vicinity of the UC
  campus are 95060 (Santa Cruz west of the river),
  95062 (Live Oak), 95064 (UCSC), 95065 (East Santa
  Cruz), 95066 (Scotts Valley).
• Suppose you wanted to extract from a file called
  addresses, containing one full name and address
  on each line, just the addresses of people living
  in these areas. Assume some people type a space
  after CA and others don't, and some write several
  spaces.
• The following regular expression describes the
  set of zipcodes you want
• CA 9506024-6.
• This grep command will find just the lines in the
  file addresses that contain zipcodes for people
  who live in near the campus
• grep 'CA 9506024-6' addresses

26
Searching for something in a filegrep

• Example
• Suppose you want only the 9-digit zipcodes,
  that's easy too
• grep 'CA 9506024-6-0-9\4\' addresses

27
Searching for something in a filegrep

• Example
• Suppose you were looking to see whether there
  were any words beginning with a in a file called
  shakespeare.
• You might type
• grep a shakespeare

28
Searching for something in a fileegrep

• Some simple tasks would be a bit of a chore just
  using grep. Suppose we wanted to add Ben Lomond
  (CA 95005), Davenport (CA 95017), and Felton
  (CA 95018). What we need here is the disjunction
  for the 5-digit zipcodes, the strings we want
  will match either CA 9506024-6 or CA 95005 or
  CA 950178 or.
• Now, we can certainly do that we can simply call
  grep three separate times, and amalgamate all the
  results. We cannot amalgamate all the searches
  into something like CA 950016024-8, because
  that defines a set that is too big it lets in
  95004, for example, and that's Aromas, way the
  other side of Watsonville.
• The way to do it is to use the extended regular
  expressons provided by the egrep program. In
  egrep, you can use parentheses to group parts of
  the expression and the pipe symbol to mean or. So
  (AB)C means "either AB or C", while A(BC) means
  "A followed by either B or C", and so on. Thus we
  could use egrep 'CA 950((05)(6024-6)(178)
  )' addressesThere are a few other things that
  egrep allows but grep does not. For example, in
  egrep regular expressions you can say a to mean
  "a sequence of one or more as", or a-z to mean
  "a sequence of one or more lower-case letters".
  In grep regular expressions you would have to say
  aa and a-za-z respectively to get these
  effects.

29
Searching for something in a fileegrep

• The way to do it is to use the extended regular
  expressons provided by the egrep program. In
  egrep, you can use parentheses to group parts of
  the expression and the pipe symbol to mean or. So
  (AB)C means "either AB or C", while A(BC) means
  "A followed by either B or C", and so on. Thus we
  could use egrep 'CA 950((05)(6024-6)(178)
  )' addressesThere are a few other things that
  egrep allows but grep does not. For example, in
  egrep regular expressions you can say a to mean
  "a sequence of one or more as", or a-z to mean
  "a sequence of one or more lower-case letters".
  In grep regular expressions you would have to say
  aa and a-za-z respectively to get these
  effects.

30
Searching for something in a fileegrep

• So we can use
• egrep 'CA 950((05)(6024-6)(178))'
  addresses
• There are a few other things that egrep allows
  but grep does not. For example, in egrep regular
  expressions you can say a to mean "a sequence of
  one or more as", or a-z to mean "a sequence of
  one or more lower-case letters". In grep regular
  expressions you would have to say aa and
  a-za-z respectively to get these effects.

31
File Management with Shell Commands

• Changing to another directory
• cd .. RETURN go up a directory tree
• cd DIRECTORY RETURN change to a
  subdirectory
• cd /tmp to change to some other
  directory on the system,
• you must type the full path name

32
File Management with Shell Commands

• Create a directory
• mkdir DIRECTORY.NAME RETURN
• Remove a directory
• rmdir DIRECTORY.NAME RETURN

33
Searching for something in a file

• cd ..
• cd c6932aab
• ls
• display shakespeare
• cp shakespeare c6932aad
• cd
• ls
• shakespeare

34
Searching for something in a file

• grep options pattern filenames
• fgrep options string filenames
• fgrep (or "fast grep") only searches for strings
• grep is a full-blown regular-expression matcher
• Some of the valid options are
• -i case-insensitive search
• -n show the line along with the matched line
• -v invert match, e.g. find all lines that do
  NOT match
• -w match entire words, rather than substrings

35
Searching for something in a filewith GREP

• grep -inw thou" shakespeare
• find all instances of the word though" in the
  file shakespeare, case-insensitive but whole
  words and display the line numbers

36
Grep

• grep 'smug' files 'smug' at the start
  of a line
• grep 'smug' files 'smug' at the end of
  a line
• grep 'smug' files lines containing
  only 'smug'
• grep '\s' files lines starting with
  's'
• grep 'Ssmug' files search for 'Smug' or
  'smug'
• grep 'BoObB' files search for BOB, Bob,
  BOb or BoB
• grep '' files search for blank
  lines
• grep '0-90-9' file search for pairs of
  numeric digits

37
Grep

• grep 'a-zA-Z0-9 anything not a
  letter or number
• grep '0-9\3\-0-9\4\' 999-9999,
  like phone numbers
• grep '.' lines with
  exactly one character
• grep '"smug"' 'smug'
  within double quotes
• grep '"smug"' 'smug', with or
  without quotes
• grep '\.' any line that
  starts with "."
• grep '\.a-za-z' line start with "."
  and 2 lc letters

38
Egrep

• The version of grep that supports the full set of
  operators mentioned above is generally called
  egrep
• (for extended grep)
• egrep '(minemy)' shakespeare