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awk - PowerPoint PPT Presentation


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awk. awk [- F r egexp ] program [ arg … ] or awk [- F r egexp ]-f progfile [ arg … ] -F defines field separator -f read program from file progfile instead on command line. awk program structure. BEGIN{ …. } action performed only once at beginning

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slide1
awk

awk [-Fregexp]program [arg …]

or

awk [-Fregexp]-f progfile [arg …]

-F defines field separator

-f read program from file progfile instead on command line

awk program structure
awk program structure

BEGIN{ …. } action performed only once at beginning

END{ … } action performed only at end after eof has been encountered.

{ … } group of actions to be performed for each input line

pattern{ … } perform group of actions for each line that satisfies pattern.

$1, $2, $3,… refer to fields on a line

$0 refers to entire line

Examples of pattern: regular expression delimited by / / or arithmetic expression like $3 > 0

example print name and balance
Example: Print name and balance

File Customer

78902:67.89:Henry Bunyan

99078:782.90:Boxcar Bertha

12345:450.00:Happy Jack

77777:78.99:Lucky Linda

slide4
% awk -F: '{print $3, "\t\$" $2}' customer

Henry Bunyan $67.89

Boxcar Bertha $782.90

Happy Jack $450.00

Lucky Linda $78.99

if no field separator is specified default is white space
If no field separator is specified default is white space

Example

% finger

Login Name TTY Idle When Office

chenjw Jianwei Chen p0 Thu 23:27

bermanka Kenneth Berman p2 Tue 07:03

hughlel Lenny Hughley *q1 3d Wed 09:52

guptaak Amit Gupta qd 19d Wed 10:55

% finger | awk '{print $3, $2, $4}'

TTY Name Idle

Chen Jianwei p0

Berman Kenneth p2

Hughley Lenny *q1

Gupta Amit qd

example preparing an index file
Example: Preparing an index file

File Index1

Unix 1

C++ 99

sed 2

awk 26

Unix 53

Oz 7

sed 14

cut 43

Unix 10

sed 8

C++ 14

awk 88

slide7
File Index2

awk 101

emacs 26

vi 23

sed 89

awk 6

pipe 5

filter 4

cut 29

emacs 199

Oz 12

merged index file
Merged index file

awk 6,26,88,101

C++ 14,99

cut 29,43

emacs 26,199

filter 4

Oz 7,12

pipe 5

sed 2,8,14,89

Unix 1,10,53

vi 23

creating index file index final by combining index1 and index2
Creating index file index.final by combining index1 and index2

sort +0f -1 +0 -1 +1n index1 index2 > index.sorted

awk -f index.awk index.sorted > index.final

index awk
index.awk

BEGIN { i = 0; }

$1 == pre { printf(",%s", $2); }

$1 != pre { if (i > 0)

{ printf("\n%s\t%s",$1,$2); }

else

{ printf("%s\t%s",$1,$2); i = 1; }

pre = $1;

}

END { printf("\n"); }

saving and distributing of files
Saving and distributing of files
  • Saving of a file
    • tar cvf filename.tarname1 name2 ..
    • compress filename.tar
  • Generated file with name filename.tar.z
  • To restore
    • uncompressfilename.tar.z
    • tarfilename.tar
  • Will restore entire hierarchy of directories name1, name2
interactive use of the shell
Interactive use of the Shell
  • Prompt for the Bourne shell family $
      • sh Bourne, AT&T mid 70’s
      • ksh Korn, AT&T 1988 and 1993
      • bash Bourne again Shell Free Software Foundation 1989
      • zsh Falstad , Princeton 1990
  • Prompt for C shell family %
      • csh Berkeley early 80’s
      • tcsh Carnegie Mellon, OSU mid 80’s
what does a shell do
What does a shell do?

Do forever {

Display prompt

Read input until ^M

Perform any substitutions

Execute command

Wait until command sends FINISH signal

}

Shell will terminate until one of the following commands is received: logout, login or ^D (and ignoreeof has not been set)

starting a shell
Starting a shell
  • Shells are kept in directory /bin/
  • To start a new shell enter /bin/sh, or /bin/csh, or /bin/ksh etc.
  • The file /etc/passwd determines with which shell your session starts up. (On OZ default /usr/local/profile), compiled version of /usr/local/profile.c
  • The shells read (and execute) certain files with special names:
    • The C-shell uses .cshrc, .login and .logout
    • The Bourne shell uses .profile