MisNotasLinux_blog: Tutorial sobre perl (...en construcción)

El lenguaje perl esta especialmente indicado para el manejo de ficheros y la depuración de texto. Según me ha comentado una mogo que está ahora progrmando con él tiene unas expresioner regulares muy potentes y sencillas.
... ya veremos.

COMADOS Y ESTRUCTURAS BÁSICAS DEL PERL

1) Para confirmar si esta instalado el intérprete perl:

# perl -v

This is perl, v5.10.0 built for i486-linux-gnu-thread-multi

Copyright 1987-2007, Larry Wall

Perl may be copied only under the terms of either the Artistic License or the GNU General Public License, which may be found in the Perl 5 source kit.

Complete documentation for Perl, including FAQ lists, should be found on this system using "man perl" or "perldoc perl". If you have access to the Internet, point your browser at http://www.perl.org/, the Perl Home Page.

2) Para ver la ruta de perl:

#which perl

/usr/bin/perl

los scripts de perl deben comenzar indicando la ruta del interprete:
#!/usr/bin/perl

3) Variables en perl:

Escalares "$":

$NUM = 4;
$TEXT = "texto";

Arrays "@":

@NUMEROS = (1,2,3,4,5);
@DIAS = ("lunes" , "martes" , "miercoles");

Hash "%":

%DIAS = ( l =>; "lunes" , m =>; "martes" , mi =>; "miercoles"

4) Argumentos en perl:

./perlscript.pl a b c

$ARGV [0]  = a

$ARGV [1]   = b

$ARGV [2]  = c

$#ARGV = 2; indica el indice del último argumento.

5) condicional "if" , "else", "elsif":

#!/usr/bin/perl

if ($VAR == 10) {

print "Es igual a 10";

} 

if ($VAR > 10) {

print "Mayor de 10\n";

}

if ($VAR > 20){

print "Mayor de 20\n";

}

if ($VAR > 30){

print "Mayor de 30\n";

}

else {

print "Menor de 10";

}

Formas resumidas de if:

if($VAR > 10) print "Mayor de 10";

ó

print "Mayor de 10" if($VAR > 10);

6) Condicional "unless"

#!/usr/bin/perl 

print "Hola" unless ($NOHOLA = 1);

7) Bucle "while":

#!/usr/bin/perl
$T = 0;

while ($T < 5) {

print "Hola 5 veces\n";

$T = $T + 1;

}

8) Bucle "until":

#!/usr/bin/perl
$T = 1;

until ($T > 5) {

print "Hola 5 veces\n";

$T = $T + 1;

}

9) Bucle "for":

#!/usr/bin/perl

for ($T = 0 ; $T < 5 ; $T = $T + 1){

print "Hola 5 veces\n";

}

10) Bucle "foreach":

#!/usr/bin/perl

@SEMANA=("lunes" , "martes" , "..." , "y domingo");

foreach   $DIA  (@SEMANA) {

print "$DIA\n";

}

11) Abriendo archivos:

open (FILE, "file.txt");    #en modo lectura.

open (FILE, ">file.txt");   #en modo escritura.

open (FILE, ">>file.txt");  #en modo actualización.

open (FILE, ">file.txt") or print "Sin acceso al archivo";

close (FILE);

12) Escribiendo en archivos (open, print, close):

#!/usr/bin/perl

open (FILE, ">>file.txt") or die "Privilegios insuficentes\n";

print FILE "Texto añadido al archivo file.txt";

close (FILE);

13) Leyendo archivos

Podemos copiar el contenido de un archivo a una variable array, cada línea es un elemento de la matriz:

#!/usr/bin/perl

open (FILE, "file.txt");

@VAR = <FILE>;

close (FILE);

print @VAR;

Haciendo un bucle con las filas del archivo:

#!/usr/bin/perl

open (FILE, "file.txt");

while ($LINEA = <FILE>) {

print $LINEA;

}

close (FILE);

14) Quitar espacios en blaco a avariable: =~ s/ //g

#!/usr/bin/perl 

$FRASE = "Frase con esapacios";

print "$FRASE\n"; 

$FRASE =~ s/ //g;

print "$FRASE\n";

result:

Frase con esapacios

Fraseconesapacios 

15) Expresiones regulares en perl:

Pattern	Matches
^A	"A" at the beginning of a line
A$	"A" at the end of a line
A^	"A^" anywhere on a line
$A	"$A" anywhere on a line
^^	"^" at the beginning of a line
$$	"$" at the end of a line

Regular Expression	Matches
[]	The characters "[]"
[0]	The character "0"
[0-9]	Any number
[^0-9]	Any character other than a number
[-0-9]	Any number or a "-"
[0-9-]	Any number or a "-"
[^-0-9]	Any character except a number or a "-"
[]0-9]	Any number or a "]"
[0-9]]	Any number followed by a "]"
[0-9-z]	Any number,
	or any character between "9" and "z".
[0-9\-a\]]	Any number, or
	a "-", a "a", or a "]"

Regular Expression	Matches
_
*	Any line with an asterisk
\*	Any line with an asterisk
\\	Any line with a backslash
^*	Any line starting with an asterisk
^A*	Any line
^A\*	Any line starting with an "A*"
^AA*	Any line if it starts with one "A"
^AA*B	Any line with one or more "A"'s followed by a "B"
^A\{4,8\}B	Any line starting with 4, 5, 6, 7 or 8 "A"'s
	followed by a "B"
^A\{4,\}B	Any line starting with 4 or more "A"'s
	followed by a "B"
^A\{4\}B	Any line starting with "AAAAB"
\{4,8\}	Any line with "{4,8}"
A{4,8}	Any line with "A{4,8}"

Regular Expression	Class	Type	Meaning
_
.	all	Character Set	A single character (except newline)
^	all	Anchor	Beginning of line
$	all	Anchor	End of line
[...]	all	Character Set	Range of characters
*	all	Modifier	zero or more duplicates
\<	Basic	Anchor	Beginning of word
\>	Basic	Anchor	End of word
$..$	Basic	Backreference	Remembers pattern
\1..\9	Basic	Reference	Recalls pattern
_+	Extended	Modifier	One or more duplicates
?	Extended	Modifier	Zero or one duplicate
\{M,N\}	Extended	Modifier	M to N Duplicates
(...\|...)	Extended	Anchor	Shows alteration
_
$...\\|...$	EMACS	Anchor	Shows alteration
\w	EMACS	Character set	Matches a letter in a word
\W	EMACS	Character set	Opposite of \w

Regular Expression
Class	Type	Meaning
\t	Character Set	tab
\n	Character Set	newline
\r	Character Set	return
\f	Character Set	form
\a	Character Set	alarm
\e	Character Set	escape
\033	Character Set	octal
\x1B	Character Set	hex
\c[	Character Set	control
\l	Character Set	lowercase
\u	Character Set	uppercase
\L	Character Set	lowercase
\U	Character Set	uppercase
\E	Character Set	end
\Q	Character Set	quote
\w	Character Set	Match a "word" character
\W	Character Set	Match a non-word character
\s	Character Set	Match a whitespace character
\S	Character Set	Match a non-whitespace character
\d	Character Set	Match a digit character
\D	Character Set	Match a non-digit character
\b	Anchor	Match a word boundary
\B	Anchor	Match a non-(word boundary)
\A	Anchor	Match only at beginning of string
\Z	Anchor	Match only at EOS, or before newline
\z	Anchor	Match only at end of string
\G	Anchor	Match only where previous m//g left off