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Sams Teach Yourself Shell Programming in 24 Hours Contents Index Hour 17: Filtering Text with awk Sections in this Chapter: Previous Chapter Next Chapter What is awk? Questions Using awk Features Terms Summary Previous Section Next Section Questions 1. Write an awk script that prints each of the fields in a record in reverse order. The output for the file fruit_prices.txt should look like the following: Quantity Price/lbs Fruit 100 $0.89 Banana 65 $0.79 Peach 22 $1.50 Kiwi 35 $1.29 Pineapple 78 $0.99 Apple (HINT: Use the for statement and NF) 2. Write an awk script that balances a checking account. Your program needs to print the balance in the account every time the user makes a transaction. The transactions are stored in a file. Each line or record in the file has the following format: command:date:comment:amount Here date is the date on which the transaction was made, comment is a string (including embedded spaces) describing the transaction, and amount is the amount of the transaction. The command determines what should be done to the balance with amount. The valid commands are ❍ B, indicates balance. When this command is encountered, the balance in the account should be set to the transaction amount. ❍ D, indicates a deposit. When this command is encountered, the transaction amount should be added to the balance. ❍ C, indicates a check. When this command is encountered, the transaction amount should be subtracted from the balance. ❍ W, indicates a withdrawal. When this command is encountered, the transaction amount should be subtracted from the balance. The main difference between the C (check) and the W (withdrawal) commands is that the C (check) command adds an extra field to its records: command:date:comment:check number:amount In addition, the B (balance) command uses only two fields:
B:amount Here amount is the balance amount in the account. For the purposes of this problem, you need to be concerned with the first field, which contains the command; the second field, which contains the transaction date; and the last field, which contains the transaction amount. The sample input file looks like the following: $ cat account.txt account.txt B:0 D:10/24/97:inital deposit:1000 C:10/25/97:credit card:101:100 W:10/30/97:gas:21.43 W:10/30/97:lunch:11.34 C:11/02/97:toner:41.45 C:11/04/97:car payment:347.23 D:11/06/97:dividend:687.34 W:11/10/97:emergency cash:200 Your output should look like the following: 10/24/97 1000.00 10/25/97 900.00 10/30/97 878.57 10/30/97 867.23 11/02/97 825.78 11/04/97 478.55 11/06/97 1165.89 11/10/97 965.89 3. Modify the program you wrote for question 2 to print the ending (total) balance after all input records have been considered. Your output should now look like the following: 10/24/97 1000.00 10/25/97 900.00 10/30/97 878.57 10/30/97 867.23 11/02/97 825.78 11/04/97 478.55 11/06/97 1165.89 11/10/97 965.89 - Total 965.89 (HINT: Use the END pattern) 4. Modify the program you wrote in question 3 to support a new command:
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Sams Teach Yourself Shell Programmi
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● Using Single Quotes ● Using D
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● Questions Hour 20: Debugging
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● Part I is an introduction to UN
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Many of the examples and the answer
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$ date [ENTER] Wed Dec 9 08:49:13 P
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anga pts/0 Dec 9 08:49 $ Here, the
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The original UNIX shell was written
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There are three major versions of k
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example, when you execute the comma
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This executes the compound command
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chmod a+x ./logins Here you are usi
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Try using the man command to get mo
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Hidden Files So far you have used l
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© Copyright Macmillan Computer Pub
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Numbering Lines The cat command als
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command $ wc -w .rhosts produces th
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produces the following error: cp: w
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m: work directory The two files are
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name. Thus both of the following fi
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../docs/ch5.doc represents the file
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changes to the directory /usr/local
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If you specify several arguments in
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Sometimes when you want to create a
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$ cp -r docs /mnt/zip/backup cp: ca
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Removing Directories You can use tw
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$ ls -ld /home/ranga This produces
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You can see the relative path by us
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Sections in this Chapter: File Type
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The permission block for this file
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Here, expression is a statement of
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For example, if the directory pub c
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Restrictions The super user, root,
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Running the same ls command as in t
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Tip - Background Processes That Wri
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the fg command. By default, the pro
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dhorvath 6770 3662 2 10:35:45 pts/6
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By default, a process runs with the
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Process Identifier --The process id
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Variable Names The name of a variab
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Array Variables The Bourne shell, s
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$ band[2]=mike $ band[3]=gene Tip -
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Hour 7: Variables Sections in this
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uses internally. Users can modify t
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Here, command is the name of a comm
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$ ls ch??.doc to accomplish this. M
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is unset. Assigning a Default Value
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It now gives this error result: Hel
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Sections in this Chapter: Quoting w
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To the shell, one or more spaces or
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Quoting Regular Expression Wildcard
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fi list5 Both the elif and the else
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Here you have an elif statement tha
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Consider the following if statement
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If you were to use the - n option i
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else echo "An error was encountered
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1. First the test [ -z "$DTHOME" ]
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esac Here the string contained in $
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The execution of a while loop proce
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5 4 3 2 1 0 6 5 4 3 2 1 0 7 6 5 4 3
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2. If the exit status of command is
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for i in 0 1 2 3 4 5 6 7 8 9 do ech
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3. When the user enters a value, $R
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The continue Command The continue c
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If you want to list the contents of
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In this version, the basename comma
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USAGE="Usage: ´basename $0´ [-c|-
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uuencoding a file. For readers who
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fi fi echo $MSG You could simplify
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● Formatting escape sequences Emb
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Name User Name Sriranga ranga Sriva
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Table 13.2 Formatting Sequence Type
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printf "%-32s " "$i" if [ -d "$i" ]
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anga ttyp0 Oct 27 19:42 (:0.0) amma
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Say you need to send a list of phon
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"Miscellaneous Tools," I will show
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$ exec 4>fd4.out associates the fil
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command > file 2>&1 list > file 2>&
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when the while loop exits, the valu
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Note - The shell uses the value of
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This function has three important p
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} OLDIFS="$IFS" IFS=: # print each
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} # set the directory to pop to the
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index.html RCS humor misc downloads
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unix has several additional pieces
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pqops.c:/* Function to delete a nod
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$ /bin/sh -nv ./buggy2.sh the outpu
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Deleting old backups, please wait..
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If you do not type a response and p
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To deactivate debugging, use either
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3 MSG="hello" 4 echo_error $MSG Her
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echo "ERROR: File $MYFILE was not f
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previous call to this function. Aft
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} Before you look at some examples
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dev/hda1 1190014 664661 463867 59%
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The number returned is in kilobytes
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getUID() { id $1 | sed -e 's/(.*$//
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63 printf "$1 (y/n)? " 64 65 if [ -
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}' 171 # Args: $1 -> the command na
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Some UNIX versions implement a work
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24 printERROR "The source $1 is not
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easily modify the script to replace
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Hour 22: Problem Solving with Shell
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To maintain your address book, you
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produces two matches: Name: Srirang
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26 # enable erasing input 27 28 stt
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2. Based on user feedback, delete t
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73 promptYESNO "Delete this entry"
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MYADDRESSBOOK="$HOME/addressbook" i
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Here, options is one or more of the
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Now that you have looked at using t
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Abstraction is a technique used to
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warning: '-' deprecated; use 'ps au
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produce the same result if the curr
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The structure of the UNIX directory
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OLDPREFIX=aaa NEWPREFIX=bbb for FIL
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history (Korn/Bash) shows the most
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Sections in this Chapter: Reserved
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^ bitwise exclusive OR operation |
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Bash array initialization USERVAR=(
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order to fix problems. default beha
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minor number UNIX uses this to asso
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important parameters. This is usual
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Sections in this Chapter: Chapter 1
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USAGE="Usage: ´basename $0´ [-v]
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Appendix C: Quiz Answers Sections i
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awk -F: ' $1 == "B" { BAL=$NF ; nex
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} if [ $DEF_TOUT -ne 0 ] ; then sle
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Sections in this Chapter: Chapter 1
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} fi if [ ! -d "$1" ] ; then printE
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numeric variables, 1st pattern-spec
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wildcards, 1st Bourne shells. See s
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(colon), 1st character, 1st, 2nd, 3
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grep, 1st, 2nd line numbers, 1st li
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stty addperson script, 1st tail, 1s
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emoving temporary files, 1st displa
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mv command, 1st, 2nd rmdir command,
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interactive mode, 1st multiple inpu
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starting directory, 1st, 2nd findin
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installation scripts disk usage, 1s
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eak command, 1st, 2nd, 3rd continue
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mvdir.sh, 1st, 2nd, 3rd, 4th, 5th,
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edirection, 1st, 2nd appending to f
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[0-9]*, 1st percent sign (%) job nu
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profiles shell specific startup wit
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hardware type, 1st, 2nd improving,
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(standard error), 1st displaying me
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prompt, 1st, 2nd, 3rd, 4th quoting
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egp command, 1st -k option sort com
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Index A B C D E F G H I J K L M N O
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