perl practical extraction and report language. perl2 scalar data n number or string of characters n...

PerlPerl

Practical Extraction and Practical Extraction and Report LanguageReport Language

Perl 2

Scalar DataScalar Data Number or string of charactersNumber or string of characters NumbersNumbers

– Internally, all numbers are double-Internally, all numbers are double-precision floating pointprecision floating point

Single-quoted stringsSingle-quoted strings– Any character, with 2 exceptions, is Any character, with 2 exceptions, is

legal between quoteslegal between quotes \' prints as \' prints as '' \\ prints as \\ prints as \\

Perl 3

Scalar DataScalar Data Double-quoted stringsDouble-quoted strings

– Backslash specifies control characters, Backslash specifies control characters, or, through octal and hex notation, any or, through octal and hex notation, any charactercharacter \n - newline\n - newline \r - carriage return\r - carriage return \t - tab\t - tab \b - backspace\b - backspace \a - bell\a - bell \e - escape\e - escape \007 - octal ASCII value\007 - octal ASCII value \x87 - hex ASCII value\x87 - hex ASCII value

Perl 4

Scalar DataScalar Data

Double-quoted stringsDouble-quoted strings \cC - control character (here, control C)\cC - control character (here, control C) \\ - backslash\\ - backslash \" - double quote\" - double quote \l - lowercase next letter\l - lowercase next letter \L - lowercase all following letters until \E\L - lowercase all following letters until \E \u - uppercase next letter\u - uppercase next letter \U - Uppercase all following letters until \E\U - Uppercase all following letters until \E \E - terminates \L or \U\E - terminates \L or \U

Perl 5


Numeric operatorsNumeric operators– Addition (+)Addition (+)– Subtraction (-)Subtraction (-)– Multiplication (*)Multiplication (*)– Division (/)Division (/)– Exponentiation (**)Exponentiation (**)– Modulus (%)Modulus (%)– Comparison operatorsComparison operators

<, <=, ==, >=, >, !=<, <=, ==, >=, >, !=

Perl 6


String operatorsString operators– Concatenation (.)Concatenation (.)– String repetition (x)String repetition (x)

"bill"x4 is "billbillbillbill""bill"x4 is "billbillbillbill" (4+2) x 3 is 6 x 3 or "6" x 3 or "666"(4+2) x 3 is 6 x 3 or "6" x 3 or "666" "a"x3.7 is "aaa""a"x3.7 is "aaa" "a"x0 is """a"x0 is ""

Perl 7


String operatorsString operators– Comparison operatorsComparison operators

lt, le, eq, ge, gt, nelt, le, eq, ge, gt, ne– 7 < 30 is true7 < 30 is true– 7 lt 30 is false7 lt 30 is false

Perl 8


Conversion between strings and Conversion between strings and numbersnumbers– String used as operand for numeric String used as operand for numeric

operatoroperator String converted to its equivalent String converted to its equivalent

numeric valuenumeric value– " 45.67bill" converts to 45.67" 45.67bill" converts to 45.67– "bill" converts to 0"bill" converts to 0

Perl 9


Conversion between strings and Conversion between strings and numbersnumbers– Numeric value used as operand for Numeric value used as operand for

string operatorstring operator Value calculated and converted into Value calculated and converted into

stringstring– "z" . (3 + 5) is "z8""z" . (3 + 5) is "z8"

Perl 10


Scalar variablesScalar variables– Begin with $, followed by letter, Begin with $, followed by letter,

possibly followed by more letters, possibly followed by more letters, digits, or underscoresdigits, or underscores

– Case sensitiveCase sensitive

Perl 11


Variable assignmentVariable assignment– Value of a scalar assignment is the Value of a scalar assignment is the

value of the right-hand sidevalue of the right-hand side– $z = 3 * ($y = 2);$z = 3 * ($y = 2);– $a = $b = 7;$a = $b = 7;

Perl 12


Binary assignment operatorsBinary assignment operators– $a = $a + 8;$a = $a + 8;

$a += 8;$a += 8;– $string = $string . "cat";$string = $string . "cat";

$string .= "cat";$string .= "cat";

Perl 13


Autoincrement and autodecrementAutoincrement and autodecrement– $z = 8;$z = 8;

$y = ++$z; #$z and $y are both 9$y = ++$z; #$z and $y are both 9– $z = 8;$z = 8;

$y = $z++; #$y is 8, but $z is 9$y = $z++; #$y is 8, but $z is 9– $z = 8.5;$z = 8.5;

$y = ++$z; #$z and $y are both 9.5$y = ++$z; #$z and $y are both 9.5

Perl 14

Scalar DataScalar Data chop( )chop( )

– Returns last character of string argumentReturns last character of string argument– Has side effect of removing this last Has side effect of removing this last

charactercharacter InterpolationInterpolation

– $a=7; print "Value is $a";$a=7; print "Value is $a"; Prints Prints Value is 7Value is 7

– $b='Bill'; print "Name is $b";$b='Bill'; print "Name is $b"; Prints Prints Name is BillName is Bill

– $b='Bill'; print "Name is \$b";$b='Bill'; print "Name is \$b"; Prints Prints Name is $bName is $b

Perl 15


<STDIN> as a scalar value<STDIN> as a scalar value– $a = <STDIN>;$a = <STDIN>;

chop($a);chop($a);– chop($a=<STDIN>);chop($a=<STDIN>);

OutputOutput– print("Hi there\n");print("Hi there\n");– print "Hi there\n";print "Hi there\n";

Perl 16


undefundef– Value of undefined variableValue of undefined variable

Looks like zero when used as a numberLooks like zero when used as a number Looks like the empty string when used as Looks like the empty string when used as

a stringa string <STDIN> returns undef when input is <STDIN> returns undef when input is

control-Dcontrol-D

Perl 17

ArraysArrays

LiteralsLiterals– (4,5,6)(4,5,6)– ("Bill",7,8,9)("Bill",7,8,9)– ($a,8)($a,8)– ($z+$h,7,8)($z+$h,7,8)– (1..5,4,7) # (1,2,3,4,5,4,7)(1..5,4,7) # (1,2,3,4,5,4,7)– (1.3..5.3) # (1.3,2.3,3.3,4.3,5.3)(1.3..5.3) # (1.3,2.3,3.3,4.3,5.3)

Perl 18

ArraysArrays

LiteralsLiterals– (2.3..7.1) # (2.3,3.3,4.3,5.3,6.3) (2.3..7.1) # (2.3,3.3,4.3,5.3,6.3) – () # the empty array() # the empty array– print (5, 6, "cat", $a)print (5, 6, "cat", $a)

Perl 19

ArraysArrays

Array variablesArray variables– Begins with @Begins with @

Array assignmentArray assignment– @a=(1,2,3);@a=(1,2,3);

@b=@a;@b=@a;– @z=5; # @z is (5)@z=5; # @z is (5)– @z=("b",6);@z=("b",6);

@w=(4,5,@z,9); # @w is (4,5,"b",6,9)@w=(4,5,@z,9); # @w is (4,5,"b",6,9)

Perl 20

ArraysArrays

Array assignmentArray assignment– ($a,$b,$c)=(4,5,6) # $a=4, $b=5, ($a,$b,$c)=(4,5,6) # $a=4, $b=5,

$c=6$c=6– ($a,$b)=($b,$a) # switches values of ($a,$b)=($b,$a) # switches values of

$a and $b$a and $b– ($z,@w)=($a,$b,$c) # $z is $a, @w is ($z,@w)=($a,$b,$c) # $z is $a, @w is

($b,$c)($b,$c)

Perl 21

ArraysArrays

Array assignmentArray assignment– $a=(4,5,6); # $a is 6, from the $a=(4,5,6); # $a is 6, from the

comma operatorcomma operator

($a)=(4,5,6); # $a is 4($a)=(4,5,6); # $a is 4

@x=(4,5,6);@x=(4,5,6);

$a=@x; # $a is 3, the length of @x$a=@x; # $a is 3, the length of @x

($a)=@x; # $a is 4($a)=@x; # $a is 4

Perl 22

ArraysArrays

Element accessElement access@x=(4,5,6);@x=(4,5,6);$a=$x[0]; # $a is 4$a=$x[0]; # $a is 4$x[0]=9; # @x is (9,5,6)$x[0]=9; # @x is (9,5,6)$x[2]++; # @x is (9,5,7)$x[2]++; # @x is (9,5,7)$x[1] += 5; # @x is (9,10,7)$x[1] += 5; # @x is (9,10,7)

($x[0],$x[1])=($x[1],$x[0]); # @x is ($x[0],$x[1])=($x[1],$x[0]); # @x is (10,9,7)(10,9,7)

Perl 23

ArraysArrays

Element accessElement access@x[0,1]=@x[1,0]; # @x is (9,10,7)@x[0,1]=@x[1,0]; # @x is (9,10,7)

@x[0,1,2]=@x[1,1,1]; # @x is @x[0,1,2]=@x[1,1,1]; # @x is (10,10,10)(10,10,10)$b=$x[8]; # $b is undef$b=$x[8]; # $b is undef$x[4] = "b"; # @x is (10,10,10,undef, $x[4] = "b"; # @x is (10,10,10,undef, "b")"b")$#x=3; # $#x is index value of last $#x=3; # $#x is index value of last element of @x, so @x is element of @x, so @x is (10,10,10,undef)(10,10,10,undef)

Perl 24

ArraysArrays

push( ) and pop( ) operatorspush( ) and pop( ) operatorspush(@x,$a); # @x = (@x,$a)push(@x,$a); # @x = (@x,$a)

push(@x,6,7,8); # @x = (@x,6,7,8)push(@x,6,7,8); # @x = (@x,6,7,8)

$last=pop(@x); # removes last $last=pop(@x); # removes last element of @xelement of @x

shift( ) and unshift( ) operatorsshift( ) and unshift( ) operatorsunshift(@x,6,7,8); # @x = (6,7,8,@x)unshift(@x,6,7,8); # @x = (6,7,8,@x)

$first=shift(@x); # ($first,@x) = @x$first=shift(@x); # ($first,@x) = @x

Perl 25

ArraysArrays

reverse( ) operatorreverse( ) operator@x = (6,7,8);@x = (6,7,8);

@y = reverse(@x); # @y = (8,7,6)@y = reverse(@x); # @y = (8,7,6) sort( ) operatorsort( ) operator

@x = (1,2,4,8,16,32,64);@x = (1,2,4,8,16,32,64);

@x = sort(@x); #@x = @x = sort(@x); #@x = (1,16,2,32,4,64,8)(1,16,2,32,4,64,8)

Perl 26

ArraysArrays

chop( ) operatorchop( ) operator@x = ("bill\n", "frank\n");@x = ("bill\n", "frank\n");

chop(@x); # @x = ("bill", "frank")chop(@x); # @x = ("bill", "frank")

Perl 27

ArraysArrays

Scalar and array contextsScalar and array contexts– Operator expecting an operand to be Operator expecting an operand to be

scalar is being evaluated in scalar is being evaluated in scalar scalar contextcontext

– Operator expecting an operand to be Operator expecting an operand to be an array is being evaluated in an array is being evaluated in array array contextcontext

Perl 28

ArraysArrays

Scalar and array contextsScalar and array contexts– Concatenating a null string to an Concatenating a null string to an

expression forces it to be evaluated in expression forces it to be evaluated in scalar contextscalar context@x = ("x", "y", "z");@x = ("x", "y", "z");

print ("There are ",@x, " elements\n"); # print ("There are ",@x, " elements\n"); # prints "xyz" for @xprints "xyz" for @x

print ("There are ", "".@x, " elements\n"); print ("There are ", "".@x, " elements\n"); # prints 3 for @x# prints 3 for @x

Perl 29

ArraysArrays

<STDIN> as an array<STDIN> as an array– In scalar context, <STDIN> returns next In scalar context, <STDIN> returns next

line of inputline of input– In array context, <STDIN> returns all the In array context, <STDIN> returns all the

remaining lines of input up to the end of fileremaining lines of input up to the end of file Each line returned as a separate element of listEach line returned as a separate element of list

@x = <STDIN>@x = <STDIN>If user types 4 lines, then presses control-D (to If user types 4 lines, then presses control-D (to indicate end-of-file), the array has 4 elementsindicate end-of-file), the array has 4 elements

Perl 30

Control StructuresControl Structures

Statement blocksStatement blocks{{

first_statement;first_statement;

……

last_statement;last_statement;

}}

Perl 31


if/unless statementif/unless statement

if (expression) {if (expression) {

first_true_statement;first_true_statement;

……

last_true_statement;last_true_statement;

}}

Perl 32


if/unless statementif/unless statement if (expression) {if (expression) {

first_true_statement;first_true_statement;……last_true_statement;last_true_statement;

} else {} else {first_false_statement;first_false_statement;……last_false_statement;last_false_statement;

}}

Perl 33

Control StructuresControl Structures if/unless statementif/unless statement

if (expression_one) {if (expression_one) {one_true_statement_first;one_true_statement_first;……one_true_statement_last;one_true_statement_last;} elseif (expression_two) {} elseif (expression_two) {two_true_statement_first;two_true_statement_first;……two_true_statement_last;two_true_statement_last;} elseif (expression_three) {} elseif (expression_three) {three_true_statement_first;three_true_statement_first;……three_true_statement_last;three_true_statement_last;} else {} else {false_statement_first;false_statement_first;……false_statement_last;false_statement_last;}}

Perl 34


if/unless statementif/unless statement

unless (expression) {unless (expression) {

statement_one;statement_one;

} else {} else {

statement_two;statement_two;

}}

Perl 35


These expressions are the only These expressions are the only ones which evaluate to falseones which evaluate to false– """"– ( )( )– "0""0"– undefundef– 00

Perl 36


while/until statementwhile/until statementwhile (expression) {while (expression) {

statement_first;statement_first;

……

statement_last;statement_last;

}}

Perl 37


while/until statementwhile/until statementuntil (expression) {until (expression) {


……


}}

Perl 38


for statementfor statementfor (initial_exp; test_exp; for (initial_exp; test_exp;

increment_exp) {increment_exp) {


……


}}

Perl 39


for statementfor statementinitial_exp;initial_exp;

while (test_exp) {while (test_exp) {


……


increment_exp;increment_exp;

}}

Perl 40


foreach statementforeach statementforeach $a (@some_list) {foreach $a (@some_list) {


……


}}

Perl 41


foreach statementforeach statement@x = (1,2,3,4,5);@x = (1,2,3,4,5);

foreach $y (reverse @x) {foreach $y (reverse @x) {

print $y;print $y;

} # prints 54321} # prints 54321

Perl 42


foreach statementforeach statement– If scalar variable is missing, $_ is If scalar variable is missing, $_ is

assumed assumed

@x = (1,2,3,4,5);@x = (1,2,3,4,5);

foreach (reverse @x) {foreach (reverse @x) {

print;print;

} # prints 54321} # prints 54321

Perl 43

Associative ArraysAssociative Arrays

List of items indexed by arbitrary List of items indexed by arbitrary scalars, called scalars, called keyskeys

%x is array%x is array {$key} is index{$key} is index

$x{"Bill"} = 45.67;$x{"Bill"} = 45.67; $x{45.56} = "fred";$x{45.56} = "fred";

Perl 44


Literal representationLiteral representation@x_list = %x; # x_list = ("Bill", @x_list = %x; # x_list = ("Bill", 45.67, 45.56, "fred") or (45.56, "fred", 45.67, 45.56, "fred") or (45.56, "fred", "Bill", 45.67)"Bill", 45.67)

%y = @x_list;%y = @x_list;

%y = %x;%y = %x;

%y = ("Bill", 45.67, 45.56, "fred");%y = ("Bill", 45.67, 45.56, "fred");

Perl 45


keys( ) operatorkeys( ) operator@z = keys(%x); # @z=("Bill",45.56) @z = keys(%x); # @z=("Bill",45.56) or or (45.56, "Bill")(45.56, "Bill")

values( ) operatorvalues( ) operator@z = values(%x); # @z=(45.67, @z = values(%x); # @z=(45.67, "fred") "fred") or ("fred",45.67)or ("fred",45.67)

Perl 46


each( ) operatoreach( ) operator– each (%array) returns the nextkey-value each (%array) returns the nextkey-value

pairpair

while (($first,$last) = each(%last)) {while (($first,$last) = each(%last)) {

print "The last name of $first is print "The last name of $first is $last\n"$last\n"

delete( ) operatordelete( ) operator%x = ("aa", "bb", 5.6, 8.77);%x = ("aa", "bb", 5.6, 8.77);

delete $x{"aa"}delete $x{"aa"}

Perl 47

Basic I/OBasic I/O

Input from <STDIN>Input from <STDIN>while ($_ = <STDIN>) {while ($_ = <STDIN>) {chop $_;chop $_;……}}

while (<STDIN>) {while (<STDIN>) {chop;chop;……}}

Perl 48

Basic I/OBasic I/O

Input from the diamond operator <>Input from the diamond operator <>– Gets data from files specified on the Gets data from files specified on the

command line that invoked given Perl command line that invoked given Perl programprogram If no files on command line, the diamond If no files on command line, the diamond

operator reads from standard inputoperator reads from standard input

while (<>) {while (<>) {

print $_;print $_;

}}

Perl 49

Basic I/OBasic I/O

Input from the diamond operator <>Input from the diamond operator <>– Actually, diamond operator gets its input Actually, diamond operator gets its input

by examining @ARGV, the array which is a by examining @ARGV, the array which is a list of command line argumentslist of command line arguments Can set this array in programCan set this array in program

@ARGV = ("aa", "bb", "cc");@ARGV = ("aa", "bb", "cc");

while (<>) { # processes files aa, bb, and ccwhile (<>) { # processes files aa, bb, and cc

print "This line of the file is: $_";print "This line of the file is: $_";

}}

Perl 50

Basic I/OBasic I/O

Output to STDOUTOutput to STDOUT– print operatorprint operator

Argument is a list of stringsArgument is a list of strings Return value is true or false, depending Return value is true or false, depending

on success of the outputon success of the output

$x = print("Hello", " world", "\n");$x = print("Hello", " world", "\n");

– Formatted outputFormatted outputprintf "%9s %4d %12.5f\n", $s, $n, $r;printf "%9s %4d %12.5f\n", $s, $n, $r;

Perl 51

Regular ExpressionsRegular Expressions

Enclosed in-between slashesEnclosed in-between slashes Checking for occurrence in $_Checking for occurrence in $_

if (/abc/) {if (/abc/) {print $_;print $_;

}}while (<>) {while (<>) {

if (/ab*c/) {if (/ab*c/) {print $_;print $_;

}}}}

Perl 52


Single-character patternsSingle-character patterns– A single character matches itselfA single character matches itself– The dot . matches any single The dot . matches any single

character except the newline (\n)character except the newline (\n)

Perl 53


Single-character patternsSingle-character patterns– A character class is represented by a A character class is represented by a

list of characters enclosed between [ ]list of characters enclosed between [ ] For the pattern to match, one and only For the pattern to match, one and only

one of these characters must be presentone of these characters must be present [abcde][abcde] [aeiouAEIOU][aeiouAEIOU] [0-9][0-9] [a-zA-Z0-9][a-zA-Z0-9]

Perl 54


Single-character patternsSingle-character patterns– Negated character classNegated character class

[^0-9][^0-9]– Matches any character except a digitMatches any character except a digit

[^aeiouAEIOU][^aeiouAEIOU]– Matches any single non-vowelMatches any single non-vowel

Perl 55


Single-character patternsSingle-character patterns– Predefined character classesPredefined character classes

\d\d– digitsdigits– [0-9][0-9]

\D\D– not digitsnot digits– [^0-9][^0-9]

Perl 56


Single-character patternsSingle-character patterns– Predefined character classesPredefined character classes

\w\w– wordswords– [a-zA-Z0-9_][a-zA-Z0-9_]

\W\W– not wordsnot words– [^a-zA-Z0-9_][^a-zA-Z0-9_]

\s\s– spacespace– [\r\t\n\f][\r\t\n\f]

\S\S– not spacenot space– [^\r\t\n\f][^\r\t\n\f]

Perl 57


Grouping patternsGrouping patterns– SequenceSequence

abcabc matches matches aa followed by followed by bb followed by followed by cc

– MultipliersMultipliers **

– 0 or more0 or more ++

– 1 or more1 or more ??

– 0 or 10 or 1

Perl 58


Grouping patternsGrouping patterns– MultipliersMultipliers

{n,m}{n,m}– Between n and m occurrences inclusiveBetween n and m occurrences inclusive

{n,}{n,}– At least n occurrencesAt least n occurrences

{n}{n}– Exactly n occurrencesExactly n occurrences

Thus, * is {0,}, + is {1,}, and ? is {0,1}Thus, * is {0,}, + is {1,}, and ? is {0,1}

Perl 60


– All matching is greedyAll matching is greedy Longest expression matches firstLongest expression matches first In "a yyy c yyyyyyyy c yyy d", the pattern In "a yyy c yyyyyyyy c yyy d", the pattern

"a.*c.*d" induces a match of the first ".*" "a.*c.*d" induces a match of the first ".*" on " yyy c yyyyyyyy "on " yyy c yyyyyyyy "

Consider the pattern "a.*cx.*d" matching Consider the pattern "a.*cx.*d" matching the string "a yyy cx yyyyyyyy cy yyy d"the string "a yyy cx yyyyyyyy cy yyy d"

– The first ".*" first matches the substring " yyy The first ".*" first matches the substring " yyy cx yyyyyyyy ", and then backtracking occurscx yyyyyyyy ", and then backtracking occurs

Perl 61


– Parentheses as memoryParentheses as memory Parentheses around a pattern causes the Parentheses around a pattern causes the

part of the string which matches this part of the string which matches this pattern to be remembered, so that it can pattern to be remembered, so that it can be later referencedbe later referenced

Consider /bill(.)fred\1/ versus /bill.fred./Consider /bill(.)fred\1/ versus /bill.fred./ /a(.)b(.)c\2d\1//a(.)b(.)c\2d\1/ /a(.*)b\1c//a(.*)b\1c/

Perl 62


Anchoring patternsAnchoring patterns– Normally, beginning of pattern is Normally, beginning of pattern is

shifted through the string from left to shifted through the string from left to rightright

– Anchoring ensures that parts of the Anchoring ensures that parts of the pattern match with particular parts of pattern match with particular parts of the stringthe string

Perl 63


Anchoring patternsAnchoring patterns– \b requires a word boundary at the given \b requires a word boundary at the given

spot in order for the pattern to matchspot in order for the pattern to match Word boundary is place between \w and \W or Word boundary is place between \w and \W or

between \w and the start or end of the stringbetween \w and the start or end of the string– /car\b/ matches car but not cars/car\b/ matches car but not cars– /\bbarb/ matches "barb" and "barbara", but not /\bbarb/ matches "barb" and "barbara", but not

"ebarb""ebarb"– /\bport\b/ matches "port", but neither "sport" nor /\bport\b/ matches "port", but neither "sport" nor

"ports""ports"

Perl 64


Anchoring patternsAnchoring patterns– \B requires that there not be a word \B requires that there not be a word

boundaryboundary /\bFred\B/ matches "Frederick" but not "Fred /\bFred\B/ matches "Frederick" but not "Fred

Flintstone"Flintstone"

– The caret (^) matches the beginning of The caret (^) matches the beginning of the string if it makes sensethe string if it makes sense /^a/ matches "a" if it is the first character of /^a/ matches "a" if it is the first character of

the stringthe string /a^/ matches "a^" anywhere in the string/a^/ matches "a^" anywhere in the string

Perl 65


Anchoring patternsAnchoring patterns– The dollar sign ($) matches the end of The dollar sign ($) matches the end of

the string if it makes sensethe string if it makes sense

Perl 66


PrecedencePrecedence– ParenthesesParentheses

( )( )

– MultipliersMultipliers + * ? {n,m}+ * ? {n,m}

– Sequence and anchoringSequence and anchoring abc ^ $ \b \Babc ^ $ \b \B

– AlternationAlternation ||

Perl 67


Selecting a different targetSelecting a different target– Want to match a variable other than $_Want to match a variable other than $_– The operator =~ matches the left-hand The operator =~ matches the left-hand

argumentargument$a = "hello world";$a = "hello world";$a =~ /^he/; # true$a =~ /^he/; # true$a =~ /(.)\1/; # true, matches the $a =~ /(.)\1/; # true, matches the

double ldouble l if ($a =~ /(.)\1/) { # trueif ($a =~ /(.)\1/) { # true

……}}

Perl 68


Selecting a different targetSelecting a different targetif (<STDIN> =~ /^[yY]/) {if (<STDIN> =~ /^[yY]/) {

……

}}

if (<STDIN> =~ /^y/i) { # i ignores caseif (<STDIN> =~ /^y/i) { # i ignores case

……

}}

Perl 69


Using a different delimiterUsing a different delimiter– If regular expression contains "/", If regular expression contains "/",

precede it with a "\"precede it with a "\"

$path = <STDIN>;$path = <STDIN>;

if ($path =~ /^\/usr\/etc/) if ($path =~ /^\/usr\/etc/) {{

……

}}

Perl 70


Using a different delimiterUsing a different delimiter$path = <STDIN>;$path = <STDIN>;

if ($path =~ if ($path =~ m#^/usr/etc#) {m#^/usr/etc#) {

……

}}

Perl 71


Using variable interpolationUsing variable interpolation$what = "is";$what = "is";

$sentence = "This is good.";$sentence = "This is good.";

if ($sentence =~ /\b$what\b/) {if ($sentence =~ /\b$what\b/) {

print "This sentence print "This sentence contains the contains the word word $what.\n"$what.\n"

}}

Perl 72


Special read-only variablesSpecial read-only variables– After successful match, $1, $2, … are After successful match, $1, $2, … are

set to same values as \1, \2, …set to same values as \1, \2, …

$_ = "This is good";$_ = "This is good";

/(\w+)\W+(\w+)/; # matches /(\w+)\W+(\w+)/; # matches first two first two wordswords

# $1 is "This" and $2 is "is"# $1 is "This" and $2 is "is"

Perl 73


Special read-only variablesSpecial read-only variables$_ = "This is good";$_ = "This is good";

($first,$second) = /(\w+)\W+(\($first,$second) = /(\w+)\W+(\w+)/;w+)/;

# $first is "This" and $second is # $first is "This" and $second is "is""is"

Perl 74


Special read-only variablesSpecial read-only variables– $& is the part of the string that $& is the part of the string that

matches the regular expressionmatches the regular expression– $` is the part of the string before the $` is the part of the string before the

part that matched the regular part that matched the regular expressionexpression

– $' is the part of the string after the $' is the part of the string after the part that matched the regular part that matched the regular expressionexpression

Perl 75


Special read-only variablesSpecial read-only variables$_ = "this is a sample string";$_ = "this is a sample string";

/sa.*le/; # matches "sample"/sa.*le/; # matches "sample"

# $` is "this is a "# $` is "this is a "

# $& is "sample"# $& is "sample"

# $' is " string"# $' is " string"

Perl 76


SubstitutionsSubstitutions– s/regular_expression/replacement_string/s/regular_expression/replacement_string/– Replaces first occurrenceReplaces first occurrence

$_ = "bill yyyyyyy fred";$_ = "bill yyyyyyy fred";

s/y*/tom/; # $_ is now "bill tom fred"s/y*/tom/; # $_ is now "bill tom fred"– Flag "g" substitutes all occurrencesFlag "g" substitutes all occurrences

$_ = "foot fool buffoon";$_ = "foot fool buffoon";

s/foo/bar/g; # $_ is now "bart barl s/foo/bar/g; # $_ is now "bart barl bufbarn"bufbarn"

Perl 77


SubstitutionsSubstitutions$_ = "hello world";$_ = "hello world";

$new = "goodbye";$new = "goodbye";

s/hello/$new/; # $_ is now s/hello/$new/; # $_ is now "goodbye "goodbye world"world"

Perl 78


SubstitutionsSubstitutions$_ = "this is a test";$_ = "this is a test";

s/(\w+)/<$1>/g; # $_ is now s/(\w+)/<$1>/g; # $_ is now "<this> <is> <a> <test>""<this> <is> <a> <test>"

$x[$j] =~ s/here/there/;$x[$j] =~ s/here/there/;

$d{"abc"} =~ s/there/here/;$d{"abc"} =~ s/there/here/;

Perl 79


split( ) operatorsplit( ) operator– Takes as arguments a regular Takes as arguments a regular

expression and a string, looks for all expression and a string, looks for all occurrences of the regular expression occurrences of the regular expression in the string, and the parts of the in the string, and the parts of the string that don’t match the regular string that don’t match the regular expression are returned in sequence expression are returned in sequence as a list of valuesas a list of values

Perl 80


split( ) operatorsplit( ) operator$line="67;bill;;/usr/bin;joe";$line="67;bill;;/usr/bin;joe";

@fields=split(/;/,$line);@fields=split(/;/,$line);

# @fields is # @fields is ("67","bill","","/usr/bin","joe")("67","bill","","/usr/bin","joe")

@fields=split(/;+/,$line);@fields=split(/;+/,$line);

# @fields is ("67", "bill", "/usr/bin", # @fields is ("67", "bill", "/usr/bin", "joe")"joe")

Perl 81


split( ) operatorsplit( ) operator– split(/regex/)split(/regex/) is the same as is the same as

split(/regex/,$_)split(/regex/,$_)– splitsplit is the same as is the same as split(/\s+/,$_)split(/\s+/,$_)

Perl 82


join ( ) operatorjoin ( ) operator– Inverse of split( )Inverse of split( )– Takes a list of values and puts them Takes a list of values and puts them

together with a separator element together with a separator element between each pair of itemsbetween each pair of items

$line = join(";",@fields); # see $line = join(";",@fields); # see previous previous slidesslides

Perl 83

FunctionsFunctions

Defining a functionDefining a functionsub repeat {sub repeat {

print "Hello, $word\n"print "Hello, $word\n"}}

– Subroutine definitions can be anywhere in Subroutine definitions can be anywhere in program textprogram text

– Subroutine definitions are globalSubroutine definitions are global For two subroutines with same name, the For two subroutines with same name, the

latter one overrides the former onelatter one overrides the former one

– By default, any variable reference inside a By default, any variable reference inside a subroutine is globalsubroutine is global

Perl 84

FunctionsFunctions

Invoking a functionInvoking a function– &repeat;&repeat;– $x = 5+&repeat;$x = 5+&repeat;

Return ValuesReturn Values– Return value of a subroutine is the value Return value of a subroutine is the value

of the logically last expression evaluatedof the logically last expression evaluatedsub sum_of_a_and_b {sub sum_of_a_and_b {

$a+$b;$a+$b;

}}

Perl 85

FunctionsFunctions

Return valuesReturn values$a=7; $b=8;$a=7; $b=8;$x=3*&sum_of_a_and_b;$x=3*&sum_of_a_and_b;

sub list_of_a_and_b {sub list_of_a_and_b {($a,$b);($a,$b);

}}

$a=7; $b=8;$a=7; $b=8;@x=&list_of_a_and_b;@x=&list_of_a_and_b;

Perl 86

FunctionsFunctions

Return valuesReturn valuessub a_or_b {sub a_or_b {

if ($a>0) {if ($a>0) {print "Write a: $a\n";print "Write a: $a\n";$a;$a;

} else {} else {print "Write b: $b\n";print "Write b: $b\n";$b;$b;

}}}}

Perl 87

FunctionsFunctions

ArgumentsArguments– Invoking a subroutine with arguments Invoking a subroutine with arguments

in parentheses puts these arguments in parentheses puts these arguments into a list denoted by @_ for the into a list denoted by @_ for the duration of the subroutineduration of the subroutine

Perl 88

FunctionsFunctions

ArgumentsArgumentssub say {sub say {

print "$_[0], $_[1]!\n";print "$_[0], $_[1]!\n";

} }

&say("goodbye", "cruel world");&say("goodbye", "cruel world");

&say("hello", "world");&say("hello", "world");

Perl 89

FunctionsFunctions

ArgumentsArguments– @_ is local to the subroutine@_ is local to the subroutine

sub add {sub add {$sum = 0;$sum = 0;foreach $_ (@_) {foreach $_ (@_) {

$sum += $_;$sum += $_;}}$sum;$sum;

}}

$a = &add(4,5,6); # adds 4, 5, 6 and assigns 15 to $a$a = &add(4,5,6); # adds 4, 5, 6 and assigns 15 to $aprint &add(6,7,8,9);print &add(6,7,8,9);print &add(6..9);print &add(6..9);

Perl 90

FunctionsFunctions

Local VariablesLocal Variablessub bigger_than {sub bigger_than {

local($n,@values);local($n,@values);($n,@values) = @_; # or local($n,@values) ($n,@values) = @_; # or local($n,@values) =@_=@_local(@result);local(@result);foreach $_ (@values) {foreach $_ (@values) {if ($_ > $n) {if ($_ > $n) {push(@result,$_);push(@result,$_);}}}}@result;@result;

}}

Perl 91

FunctionsFunctions

Local variablesLocal variables@new=&bigger_than(100,@list); @new=&bigger_than(100,@list);

#@new #@new gets elements of @list > gets elements of @list > 100100

@x = &bigger_than(5,1,5,15,67); @x = &bigger_than(5,1,5,15,67); #@x= #@x= (15, 67)(15, 67)

Perl 92

Miscellaneous Control Miscellaneous Control StructuresStructures

lastlast– Exits a loopExits a loop

nextnext– Begins another loop iterationBegins another loop iteration

redoredo– Jumps to the top of a loop without Jumps to the top of a loop without

beginning another iterationbeginning another iteration

Perl 93


@movies = ("Star Wars", "Porky's", "Rocky @movies = ("Star Wars", "Porky's", "Rocky 5", "Terminator", "Babe”);5", "Terminator", "Babe”);

@ratings = ("PG", "R", "PG-13", "R", "G");@ratings = ("PG", "R", "PG-13", "R", "G");

for ($j=0, $j<=4, $j++) {for ($j=0, $j<=4, $j++) {next if $ratings[$j] eq 'R';next if $ratings[$j] eq 'R';print "Would you like to see $movie[$j]?";print "Would you like to see $movie[$j]?";chop($answer = <>);chop($answer = <>);last if $answer eq 'yes';last if $answer eq 'yes';

}}if ($answer eq 'yes') {print "That will be \if ($answer eq 'yes') {print "That will be \

$4.25\n"}$4.25\n"}else {print "Sorry you don't see anything you else {print "Sorry you don't see anything you

like.\n"}like.\n"}

Perl 94


print "Type in 4 digits (0 through 9)\n\n"print "Type in 4 digits (0 through 9)\n\n"

for ($j=1; $j<=4; $j++) {for ($j=1; $j<=4; $j++) {

print "Choice $j:";print "Choice $j:";

chop($digit[$j] = <>);chop($digit[$j] = <>);

redo if $digit[$j] > 9;redo if $digit[$j] > 9;

redo if $digit[$j] < 0;redo if $digit[$j] < 0;

}}

print "Your choices: @digit \n";print "Your choices: @digit \n";

Perl 95


Labelled BlocksLabelled BlocksOUTER: for ($i=1; $i<=10; $i++) {OUTER: for ($i=1; $i<=10; $i++) {

INNER: for ($j=1; $j<=10; $j++) {INNER: for ($j=1; $j<=10; $j++) {if ($i*$j == 25) {if ($i*$j == 25) {

print "$i times $j is 25!\n";print "$i times $j is 25!\n";last OUTER;last OUTER;

}}if ($j > $i) {if ($j > $i) {

next OUTER;next OUTER;}}

}}}}

Perl 96


Expression ModifiersExpression Modifiers– exp2 if exp1; # if (exp1) {exp2;}exp2 if exp1; # if (exp1) {exp2;}– exp2 unless exp1; # unless (exp1) exp2 unless exp1; # unless (exp1)

{exp2;}{exp2;}– exp2 while exp1; # while (exp1) exp2 while exp1; # while (exp1)

{exp2;}{exp2;}– exp2 until exp1; # until (exp1) exp2 until exp1; # until (exp1)

{exp2;}{exp2;}

Perl 97


&&, ||, and ?: as control structures&&, ||, and ?: as control structures– exp1 && exp2exp1 && exp2

if (exp1) {exp2;}if (exp1) {exp2;}

– exp1 || exp2exp1 || exp2 unless (exp1) {exp2;}unless (exp1) {exp2;}

– exp1 ? exp2 : exp3;exp1 ? exp2 : exp3; if (exp1) {exp2;} else {exp3;}if (exp1) {exp2;} else {exp3;}

Perl 98

Filehandles and File TestsFilehandles and File Tests

FilehandlesFilehandles– I/O connection nameI/O connection name– STDINSTDIN– STDOUTSTDOUT– STDERRSTDERR

Perl 99


Opening and closing a filehandleOpening and closing a filehandle– open(FILEHANDLE, "external_file_name")open(FILEHANDLE, "external_file_name")

Opens file for readingOpens file for reading

– open(FILEHANDLE, open(FILEHANDLE, ">external_file_name")">external_file_name") Opens file for writingOpens file for writing

– open(FILEHANDLE, open(FILEHANDLE, ">>external_file_name")">>external_file_name") Opens file for appendingOpens file for appending

Perl 100


Opening and closing a filehandleOpening and closing a filehandle– close(FILEHANDLE)close(FILEHANDLE)

Closes fileCloses file

– These operations return true or false, These operations return true or false, depending on whether or not the depending on whether or not the operation was successfuloperation was successful

– A filehandle that hasn’t been successfully A filehandle that hasn’t been successfully opened can be read (you get the end-of-opened can be read (you get the end-of-file at the start) or written to (data file at the start) or written to (data disappears)disappears)

Perl 101


Opening and closing a filehandleOpening and closing a filehandle– The die( ) operator prints out its The die( ) operator prints out its

arguments on STDERR and then ends arguments on STDERR and then ends the processthe process

unless (open(FILE, ">/x/y/data")) {unless (open(FILE, ">/x/y/data")) {die "File couldn't be opened\n";die "File couldn't be opened\n";

}}

open(FILE, ">/x/y/data") || die “File open(FILE, ">/x/y/data") || die “File couldn’t couldn’t be opened\n”;be opened\n”;

Perl 102


Using filehandlesUsing filehandlesopen(IN,"$a") || die "Cannot open $a for open(IN,"$a") || die "Cannot open $a for

reading";reading";

open(OUT, ">$b") || "Cannot create $b";open(OUT, ">$b") || "Cannot create $b";

while (<IN>) {while (<IN>) {

print OUT $_;print OUT $_;

}}

close(IN);close(IN);

close(OUT);close(OUT);

Perl 103


File testsFile testsprint "What file? ";print "What file? ";$filename=<STDIN>;$filename=<STDIN>;chop($filename);chop($filename);if (-r $filename && -w $filename) {if (-r $filename && -w $filename) {

# file exists and I can read and write it# file exists and I can read and write it……

}}

Perl 104


File testsFile tests– -x-x

File is executableFile is executable

– -e-e File or directory existsFile or directory exists

– -o-o File or directory is owned by userFile or directory is owned by user

Perl 105


File testsFile tests– -z-z

File exists and has zero sizeFile exists and has zero size

– -s-s File or directory exists and has nonzero sizeFile or directory exists and has nonzero size

– Return value is the size in bytesReturn value is the size in bytes

– -f-f Entry is a fileEntry is a file

– -d-d Entry is a directoryEntry is a directory

Perl 106


stat( ) operatorstat( ) operator– stat(FILEHANDLE)stat(FILEHANDLE)

Returns 13-element array, where Returns 13-element array, where stat(FILEHANDLE)[7] is the size of the file stat(FILEHANDLE)[7] is the size of the file in bytesin bytes

Perl 107

FormatsFormats

Defining a FormatDefining a Formatformat ADDRESSLABEL =format ADDRESSLABEL ===========================================================| @<<<<<<<<<<<<<<<<<<<<<<<<<< || @<<<<<<<<<<<<<<<<<<<<<<<<<< |$name$name| @<<<<<<<<<<<<<<<<<<<<<<<<<< || @<<<<<<<<<<<<<<<<<<<<<<<<<< |$address$address| @<<<<<<<<<<<<<<<<, @< @<<<< || @<<<<<<<<<<<<<<<<, @< @<<<< |$city, $state, $zip$city, $state, $zip==========================================================..

Perl 108

FormatsFormats

Invoking a FormatInvoking a Formatopen(ADDRESSLABEL, ">labels") | | die "Can’t open(ADDRESSLABEL, ">labels") | | die "Can’t

create";create";

open(ADDRESSES, "addresses") | | die "Can’t open(ADDRESSES, "addresses") | | die "Can’t open addresses";open addresses";

while (<ADDRESSES>) {while (<ADDRESSES>) {

($name,$address,$city,$state,$zip) = split(/:/);($name,$address,$city,$state,$zip) = split(/:/);

write ADDRESSLABEL; # This is filehandlewrite ADDRESSLABEL; # This is filehandle

# by default, format of same name is also used# by default, format of same name is also used

}}

Perl 109

FormatsFormats

Text FieldsText Fields– @<<<<@<<<<

5 spaces left-justified5 spaces left-justified

– @>>>@>>> 4 spaces right-justified4 spaces right-justified

– @| | | | |@| | | | | 6 spaces centered6 spaces centered

Numeric FieldsNumeric Fields– @###.##@###.##

Perl 110

FormatsFormats

sprintf operatorsprintf operator– Returns as a string whatever printf Returns as a string whatever printf

would have printedwould have printedformat MONEY =format MONEY =

Assets: @<<<<<<<<< Liabilities Assets: @<<<<<<<<< Liabilities @<<<<<<<< Net: @<<<<<<<<<@<<<<<<<< Net: @<<<<<<<<<

$func($assets,10), &func($liab,9), $func($assets,10), &func($liab,9), $func($assets - $liab,10)$func($assets - $liab,10)

..

Perl 111

FormatsFormats

sprintf operatorsprintf operatorsub func {sub func {

local($n, $width) = @_;local($n, $width) = @_;$width - = 2;$width - = 2;$n = sprintf("%.2f", $n);$n = sprintf("%.2f", $n);if ($n < 0) {if ($n < 0) {

sprintf("[%$width.2f]", -$n);sprintf("[%$width.2f]", -$n);} else {} else {

sprintf(" %$width.2f ", $n);sprintf(" %$width.2f ", $n);}}

}}

Perl 112

FormatsFormats

Multiline fieldsMultiline fieldsformat STDOUT =format STDOUT =Text before.Text before.@*@*$long_string$long_stringText after.Text after...

$long_string = "Bill\nFred\nSue\nTom\n";$long_string = "Bill\nFred\nSue\nTom\n";write;write;

Perl 113

FormatsFormats

Multiline fieldsMultiline fieldsText before.Text before.BillBillFredFredSueSueTomTomText after.Text after.

Perl 114

FormatsFormats

Filled fieldsFilled fields– Allows one to create a paragraph Allows one to create a paragraph

where words are broken at word where words are broken at word boundaries and lines are wrapped as boundaries and lines are wrapped as neededneeded

– Substitute ^ for @Substitute ^ for @

Perl 115

FormatsFormats Filled fieldsFilled fields

format try =format try =Name: @<<<<<<<<< Comment: Name: @<<<<<<<<< Comment:

^<<<<<<<<<<<<<^<<<<<<<<<<<<<$name, $comment$name, $comment

^<<<<<<<<<<<<<^<<<<<<<<<<<<<$comment$comment

^<<<<<<<<<<<<<^<<<<<<<<<<<<<$comment$comment. .

– $comment is changed each time to what is not $comment is changed each time to what is not yet printedyet printed

Perl 116

FormatsFormats

Filled fieldsFilled fieldsformat try =format try =Name: @<<<<<<<<< Comment: Name: @<<<<<<<<< Comment:

^<<<<<<<<<<<<<^<<<<<<<<<<<<<$name, $comment$name, $comment~ ~

^<<<<<<<<<<<<<^<<<<<<<<<<<<<$comment$comment~ ~

^<<<<<<<<<<<<<^<<<<<<<<<<<<<$comment$comment..

– ~ suppresses line if only blanks would print~ suppresses line if only blanks would print

Perl 117

FormatsFormats

Filled fieldsFilled fieldsformat try =format try =

Name: @<<<<<<<<< Comment: Name: @<<<<<<<<< Comment: ^<<<<<<<<<<<<<^<<<<<<<<<<<<<

$name, $comment$name, $comment

~~ ~~ ^<<<<<<<<<<<<<^<<<<<<<<<<<<<

$comment$comment

..– ~~ repeats this line until nothing but blanks ~~ repeats this line until nothing but blanks

are leftare left

Perl 118

FormatsFormats

Changing the FilehandleChanging the Filehandleprint "Hello world\n"; # prints to STDOUTprint "Hello world\n"; # prints to STDOUT

select(LOGFILE); # select a new filehandleselect(LOGFILE); # select a new filehandle

print "Hello world\n"; # prints to LOGFILEprint "Hello world\n"; # prints to LOGFILE

– The return value from select( ) is the The return value from select( ) is the name of the old filehandlename of the old filehandle$oldhandle = select(LOGFILE);$oldhandle = select(LOGFILE);

print "This goes to LOGFILE\n";print "This goes to LOGFILE\n";

select($oldhandle); # restores the previous select($oldhandle); # restores the previous filehandlefilehandle

Perl 119

FormatsFormats

Changing the Format NameChanging the Format Name– Default format name for a filehandle is Default format name for a filehandle is

the same as the filehandlethe same as the filehandle– Contained in variable $~Contained in variable $~– Set format for REPORT filehandle to Set format for REPORT filehandle to

NEWNEW$oldhandle = select(REPORT);$oldhandle = select(REPORT);

$~ = "NEW";$~ = "NEW";

select($oldhandle);select($oldhandle);

Perl 120

Data TransformationsData Transformations

Finding a substringFinding a substring– $y = index($string, $substring);$y = index($string, $substring);

Scans from left-to-rightScans from left-to-right

$y = index("car", "a"); # $y is 1$y = index("car", "a"); # $y is 1

$z = "fred";$z = "fred";

$y = index($z, $z); # $y is 0$y = index($z, $z); # $y is 0

$y = index($z, "ed"); # $y is 2$y = index($z, "ed"); # $y is 2

$y = index($z, "car"); # $y is -1$y = index($z, "car"); # $y is -1

Perl 121


Finding a substringFinding a substring– $x = index($string, $substring, $skip);$x = index($string, $substring, $skip);

Third parameter is the minimum value returned Third parameter is the minimum value returned by indexby index

$where=index("hello world", "l"); # $where is 2$where=index("hello world", "l"); # $where is 2

$where=index("hello world", "l",0); #$where is 2$where=index("hello world", "l",0); #$where is 2



Perl 122


Finding a substringFinding a substring– $x = rindex("string", "substring", $x = rindex("string", "substring",

$skip)$skip) Scans right-to-leftScans right-to-left

$x=rindex("hello world", "he"); # $w is 0$x=rindex("hello world", "he"); # $w is 0

$x=rindex("hello world", "l"); # $w is 9$x=rindex("hello world", "l"); # $w is 9

$x=rindex("hello world", "o",6); # $w is 4$x=rindex("hello world", "o",6); # $w is 4

Perl 123


Extracting and replacing a stringExtracting and replacing a string– $s = substr($string, $start, $length);$s = substr($string, $start, $length);

$x = "hello world!";$x = "hello world!";

$y = substr($x, 3, 2); # $y is "lo"$y = substr($x, 3, 2); # $y is "lo"

$y = substr($x, 6, 400); # $y is "world!"$y = substr($x, 6, 400); # $y is "world!"

$z = substr(“10000000000”, 0, $power+1)$z = substr(“10000000000”, 0, $power+1)

– If length < 0, the empty string is If length < 0, the empty string is returnedreturned

Perl 124


Extracting and replacing a stringExtracting and replacing a string– $start can be less than zero$start can be less than zero

Start that many characters from the rightStart that many characters from the right

$y = substr("This is a string", -3, 3); # $y is $y = substr("This is a string", -3, 3); # $y is "ing""ing"

$y = substr("This is a string", -3, 1); # $y is "i"$y = substr("This is a string", -3, 1); # $y is "i"

– Can omit $lengthCan omit $length Takes entire string from $start positionTakes entire string from $start position

$y = substr("This is a string", 5); # $y is "is a $y = substr("This is a string", 5); # $y is "is a string"string"

Perl 125


Extracting and replacing a stringExtracting and replacing a string$x = "hello world!";$x = "hello world!";

substr($x, 0, 5) = "hi there"; # $x is "hi substr($x, 0, 5) = "hi there"; # $x is "hi there world!"there world!"

substr($x, -6, 5) = "people"; # $x is "hello substr($x, -6, 5) = "people"; # $x is "hello people!"people!"

Perl 126


TransliterationTransliteration– Translate one character to anotherTranslate one character to another– Operates by default on $_Operates by default on $_

$_ = "bill and fred";$_ = "bill and fred";

tr/bf/fb/; # $_ is "fill and bred"tr/bf/fb/; # $_ is "fill and bred"

tr/abcde/ABCDE/; # $_ is "fill AnD BrED"tr/abcde/ABCDE/; # $_ is "fill AnD BrED"

tr/a-z/A-Z/; # $_ is "FILL AND BRED"tr/a-z/A-Z/; # $_ is "FILL AND BRED"

tr/A-Z/yx/; # $_ is "xxx yxx xxxx"tr/A-Z/yx/; # $_ is "xxx yxx xxxx"

$_ = "bill and fred";$_ = "bill and fred";

tr/a-z/ABCDE/d; # $_ is "B AD ED" (delete tag)tr/a-z/ABCDE/d; # $_ is "B AD ED" (delete tag)

Perl 127


TransliterationTransliteration– Return value is number of characters Return value is number of characters

changedchanged$_ = "bill and fred";$_ = "bill and fred";

$count = tr/a-z//; # $_ is unchanged but $count = tr/a-z//; # $_ is unchanged but $count is 11$count is 11

If the second list is empty and there is no If the second list is empty and there is no dd option, then result list is same as the option, then result list is same as the original listoriginal list

Perl 128

Data TransformationsData Transformations TransliterationTransliteration

– Complement Tag Complement Tag Any character in first string is removed from Any character in first string is removed from

set of 256 possible characters and remaining set of 256 possible characters and remaining characters, taken in sequence, form the characters, taken in sequence, form the resulting first stringresulting first string

$_ = "bill and fred";$_ = "bill and fred";$count = tr/a-z//c; # $_ is unchanged, $count $count = tr/a-z//c; # $_ is unchanged, $count

is 2 (non-lowercase letters are counted)is 2 (non-lowercase letters are counted)tr/a-z/_/c; # $_ is "bill_and_fred", non-tr/a-z/_/c; # $_ is "bill_and_fred", non-

lowercase letters are converted to "_"lowercase letters are converted to "_"tr/a-z//cd; # $_ is "billandfred", non-lowercase tr/a-z//cd; # $_ is "billandfred", non-lowercase

letters deletedletters deleted

Perl 129


TransliterationTransliteration– Squeeze tagSqueeze tag

$_ = "aaabbbcccdefghi";$_ = "aaabbbcccdefghi";

tr/defghi/abcddd/s; # $_ is "aaabbbcccabcd"tr/defghi/abcddd/s; # $_ is "aaabbbcccabcd"

$_ = "bill and fred, jerry and sue";$_ = "bill and fred, jerry and sue";

tr/a-z/X/s; # $_ is "X X X, X X X"tr/a-z/X/s; # $_ is "X X X, X X X"

$_ = "bill and fred, jerry and sue";$_ = "bill and fred, jerry and sue";

tr/a-z/_/cs; # $_ is tr/a-z/_/cs; # $_ is 'bill_and_fred,_jerry_and_sue"'bill_and_fred,_jerry_and_sue"

Perl 130


TransliterationTransliteration– Other targetsOther targets

$x = "bill and fred";$x = "bill and fred";

$x ~= tr/aeiou/X/; # $x is "bXll Xnd frXd"$x ~= tr/aeiou/X/; # $x is "bXll Xnd frXd"

perl practical extraction and report language. perl2 scalar data n number or string of characters n...

Documents