Perl Overview
Perl coding tips
打开pipe或者访问文件的时候，最好使用die
open FILE, "a_file" or die "Can not open file a_file: $!";
close FILE;
比die更好用的是croak
use Carp;
a("a_file"); #resume that a_file does exist
a("b_file"); #resume that b_file does not exist
sub a {
my $filename = shift;
open FILE, "$filename" or croak "Can not open file $filename: $!";
return 0;
}
用dumper来print复杂的数据结构，便于debug
use Data::Dumper;
$var = {"name" => "hello", "action" => "speak" };
print Dumper($var);
用grep和map可以节省很多代码
my @foos = grep {!/^#/} @bars; # weed out comments
my %hash = map { lc($_) => 1 } @array
my @squares = map { $_ * $_ } grep { $_ > 5 } @numbers;
使用qq代替双引号，使用q代替单引号，list赋值使用qw
$a = qq{"}; #{} is used for boundary
$b = qq!"!; #!! is the same
$c = q{'};
@vars = qw{a b c};
使用list的内置函数，不要重新发明轮子
use List::Util qw(max);
my @vars = qw(1 2 3);
my $result = max(@vars);
打印多行的信息
$a = "hello";
print <<ENDOFPRINT;
Dear Lee,
blablabla...
$a
ENDOFPRINT
$b = <<ENDOFA;
Dear friend,
I am here.
ENDOFA
只想做语法检查
perl -cwT test.pl
查看Perl默认的include路径
perl -e "print join(qq{\n}, @INC);"
使用自己的local路径下的库
use lib '/home/xx/eda_scripts/pm';
查看perl的pod格式的说明
perldoc rvp.pm
perldoc perldoc
Perl5.8之后的版本，可以在数据中间加下划线
$a = 111_222;
print "a = ", $a , "\n";
调用其他shell命令，同时获得shell命令的STDERR以及STDOUT信息
$pid = open $readme, "-|", "$cmd 2>&1";
while (<$readme>) {
push(@out, $_);
}
close $readme;
Perl使用子线程，获得子线程的STDERR信息
pipe(READER, WRITER) or die "pipe no good: $!";
my $pid = fork();
die "Can no fork: $!" unless defined $pid;
if($pid) { #parent process
close WRITER;
while(<READER>) {
push @out, $_;
}
}
else { #child process
close READER;
open STDERR, ">&WRITER";
$parser = XML::LibXML->new;
$parser->validation(1);
exit 0;
}
多线程
因为fork是复制出一个完全一样的进程，所以“go on”会被print 2 次。
my $pid = fork();
if($pid) {
#parent
print "in parent\n";
}
else {
#child
print "in child\n";
}
print "go on\n";
child process中途退出了，所以 “go on”只被print 1次
my $pid = fork();
if($pid) {
#parent
print "in parent\n";
}
else {
#child
print "in child\n";
exit;
}
print "go on\n";
child process通过exec，替换掉当前process，所以 “never print this”不会被print
my $pid = fork();
if($pid) {
#parent
print "in parent\n";
}
else {
#child
print "in child\n";
exec("ls");
print "never print this.\n";
}
print "go on\n";
eval{}是一种保护性写法。eval的运行结果放在$@里。可以结合alarm handler来完成很多应用
print STDERR "type your password: ";
my $password =
eval {
local $SIG{ALRM} = sub { die "timeout\n" };
alarm (5); # five second timeout
return <STDIN>;
};
alarm (0);
print STDERR "you timed out\n" if $@ =~ /timeout/;
reaper函数，非阻塞式（WNOHANG）的处理所有子进程，$kid等于-1的时候，表示没有需要回收的进程，跳出reaper函数
use POSIX 'WNOHANG';
$SIG{CHLD} = \&reaper;
sub reaper {
while ((my $kid = waitpid(-1,WNOHANG)) > 0) {
warn "Reaped child with PID $kid\n";
}
}
reference
类似c语言的指针
@vars = ();
$vars_ref = \@vars;
$a_href = {};
$b_href = { "name" => "b", "action" => "speak", };
$c_href = {%{$b_href}};
$tmp = "name";
print $c_href->{$tmp}, "\n"; #This is called a symbolic reference
安装module
cpan install Template
cpan install XML::Rabbit