在Perl中,可以使用defined函数来判断变量是否为空。defined函数返回一个布尔值,如果变量已经被定义且不为空,则返回真,否则返回假。 以下是一个示例: my $var1 = ""; my $var2; my $var3 = "Hello"; if (defined $var1) { print "var1 is defined\n"; } else { print "var1 is not defined\n...
$#ths ) { if ( not defined $target[$idx] ) { $target[$idx] = shift @mission; } } } #等待线程任务完结 my $wait = 1; while ( $wait ) { $wait = 0; grep { $wait = 1 if ( defined $_ ) } @target; } #线程终结和分离 grep { $_->kill('BREAK')->detach() } threads...
[% IF hostname.defined %] hostname = [% hostname %][% ELSE %][% -- a comment, variable hostname not provided %][% END %] 在the manual中对此进行了讨论。 收藏分享票数1 EN 页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持 原文链接: https://stackoverflow.com/ques...
#!/usr/bin/perl my $cmd=$ARGV[0]; my $func = eval "sub{while(<STDIN>){chomp;$cmd;}}"; die "unable to compile '$cmd', aborting...\n" if not defined $func; $func->(); 命令行调用 代码语言:javascript 代码运行次数:0 运行 AI代码解释 find . |./process_each_line.pl 'print ...
否定真正的价值! 或not返回特殊的假值。 Perl编程语言提供以下类型的条件语句。 Sr.No.声明和说明 (The ? : Operator) 我们检查conditional operator ? : conditional operator ? :可用于替换if...else语句。 它有以下一般形式 - Exp1 ? Exp2 : Exp3; 12...
print "hello" if $guest >= 1; unless模块 unless ($credit > 100) { print "You can not graduate! "; } unless语句 print "eat " unless $food == 0; 由于逻辑算子的作用,还可以写出不用关键字if或unless的判断语句,如常用的打开文件语句: open(DATA, "< $filename") or die "Can'...
if($xand$yand not$z){print"All conditions met.\n"; }else{print"Not all.\n"} 逻辑运算符短路,即一旦确定表达式是真或假,就立即停止逻辑表达式的计算,最常见的是 open(FILE,"test.txt") ordie"can't open file:$!\n"; 循环语句(与C语言完全相同) ...
perl v5.12.5 Last change: 2012-11-03 3 Perl Programmers Reference Guide PERLFAQ8(1) ReadMode('cbreak'); if (defined ($char = ReadKey(-1)) ) { # input was waiting and it was $char } else { # no input was waiting } ReadMode('normal'); # restore normal tty settings How do I...
BEGIN { use Carp::Heavy; no warnings 'redefine'; *Carp::format_arg = sub { package Carp; my $arg = shift; if( not defined $arg ) { $arg = 'undef' } elsif( ref $arg ) { use Data::Dumper; local $Data::Dumper::Indent = 0; # salt to taste local $Data::Dumper::Terse =...
if (-r $filename) { open FILE, $filename; # do something with file } else { warn "Couldn't open $filename - doesn't exist or is not readable"; } Now if we cannot read the file we do not even try to open it. But we still see a warning in error_log: Couldn't open /tmp...