小编jre*_*ger的帖子

当我遇到某种情况时,我想在没有错误的情况下退出(我知道断言和失败模块).以下代码退出但失败:

  tasks:

    - name: Check if there is something to upgrade
      shell: if apt-get --dry-run upgrade | grep -q "0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded"; then echo "no"; else echo "yes"; fi
      register: upgrading

    - name: Exit if nothing to upgrade
      fail: msg="Nothing to upgrade"
      when: upgrading.stdout == "no"

我有两个数组,我想找到一个数组但不是另一个数组的元素:

例如:

@array1 = ("abc", "cde", "fgh", "ijk", "lmn")
@array2 = ("abc", "fgh", "lmn")

我需要最终得到:

@array3 = ("cde", "ijk")

在Perl中检查引用类型时,为什么使用常量 pragma 更好:

use constant HASH => ref {};

die "I expect a hashref" unless $ref_type eq HASH;

而不是硬编码的字符串:

die "I expect a hashref" unless $ref_type eq 'HASH';

有什么优点和缺点(如果有的话)？

我正在尝试测试一段代码($code),它应该确保一次只运行一个程序实例:

#!/usr/bin/perl
# test_lock
use strict;
use warnings;

( my $code = <<'CODE') =~ s/^\s+//gm;
    #!/usr/bin/perl
    use strict;
    use warnings;
    use Fcntl qw(:flock);

    # Make sure only one instance of the program is running at a time.
    open our $Lock, '<', $0 or die "Can't lock myself $0: $!";
    flock $Lock, LOCK_EX | LOCK_NB
      or die "Another instance of $0 is already running. Exiting ...\n";

    sleep(2);
CODE

my $progfile = '/tmp/x';
open my $fh, '>', $progfile or die …

为什么length()说这是4个逻辑字符(我希望它说1):

$ perl -lwe 'print length("")'
4

我想我的期望有些不对劲.:-) 它是什么？

我理解shell变量是当前shell的本地变量,而环境变量(exported 变量)传递给shell分叉的子进程.

当我在双引号内运行Perl单行程序时,我可以从forked perl进程访问(本地)shell变量:

$ FOO=bar
$ perl -we "print qx'echo $FOO'"
bar

这是为什么？