Dpuiu Perl

Links

• [1]
• SysAdmin Perl
• Subroutines

POD

• POD; pod2html pod2latex pod2man pod2text pod2usage

In place editing

• Edit a file in place: -i

 perl -i.bck script.pl xxx
 => xxx(new), xxx.bck(old)

• dos2unix

 perl -i -pe 's/\r//g' file

• unix2dos

 perl -i -pe 's/\n/\r\n/' file

BEGIN/END blocks

 perl -ane 'BEGIN { print "sum\n"}  END { print $sum,"\n" } $sum += $F[0]; '

Regular Expressions

• Maximal match (default)

 echo $PERLLIB | perl -ane '/^(.+):/; print $1,"\n"'

• Minimal match

 echo $PERLLIB | perl -ane '/^(.+?):/; print $1,"\n"'
 /fs/sz-user-supported/Linux-x86_64/lib

• Translation: $_ =~ tr/abc/ABC/

Search directories

• -Idir : same as "use lib dir_name"

 default: /usr/include & /usr/lib/perl
 add dirs to PERLLIB env variable <=>  @INC 
 perl -e '$,="\n"; print  @INC ; '

Command line arguments

• PERL5OPT : -[DIMUdmtw] switches

Modules

• -M moldule: same as "use module_name"

 perl -MLWP::Simple -e' print head "http://www.example.com"'
 perl -e 'use LWP::Simple; print head "http://www.example.com"'

Variables

• $. : input line number
• $, : output field separator (default="")

 $ perl -e '$, = "\n";print (1,2,3,"");'
 1
 2
 3

 $ perl -e '$, = " "; @l=("a","b","c"); print map {uc($_)} @l; '
 A B C

• $/ : the input record separators (default="\n")
• $\ : output record separators (default="")

Files

• open(IN, '-') # Open standard input
• open(IN, '>-') # Open standard output
• @lines = <IN> # read all lines in the file
• $line = <IN> # read one line

Hashes

• foreach $person (keys %ages) {}
• foreach $age (values %ages) { }
• while (($person, $age) = each(%ages)) {}
• cmd hash

 my %cmd_hash = (scarf2std=>\&scarf2std, fqint2std=>\&fqint2std);  
 &{$cmd_hash{$cmd}};  
 sub scarf2std {...} 
 sub fqint2std {...}

Modules

• Getopt::Long
• File::Find

Security

File names

• use open(IN,"<" ,filename) instead of open(IN,filename)

 filename could be "rm -fr * |" 

• check file names for illegal characters

 $filename =~ /^([\w.-]+)$/)

Taint mode

 #!/usr/bin/perl -wT
 use strict;
 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};
 $ENV{PATH} = "/usr/bin/:/usr/local/bin";