Perl 编程/关键字/substr

Thesubstrkeyword

Thesubstr命令从EXPRESSION中提取并返回子字符串，其中第一个字符位于OFFSET 0处。如果OFFSET为负数，则从字符串末尾开始计数。如果LENGTH为负数，则从字符串末尾保留这么多字符。

substr也可以用作左值，如果EXPRESSION也是左值。通过分配大于或小于LENGTH的字符串，字符串将分别增长或缩小以容纳它。

如果OFFSET和LENGTH指定的子字符串部分位于字符串外部，则仅返回字符串内的部分。如果它超出了两端，则返回 undef，如果它是一个左值，则会抛出异常。

语法

  substr EXPRESSION, OFFSET, LENGTH, REPLACEMENT
  substr EXPRESSION, OFFSET, LENGTH
  substr EXPRESSION, OFFSET

示例

代码

my $name = 'Anton';

print "name = \"", $name, "\"\n";
substr($name, 5) = 'io';         # $name is now "Antonio"

print "name = \"", $name, "\"\n";
my $null = substr $name, 7, 2;   # returns "" w/o warning

print "null = \"", $null, "\"\n";
my $oops = substr $name, 8;      # returns undefined with a warning

print "oops = \"", $oops, "\"\n";
substr($name, 8) = 'gap';        # raises an exception

print "name = \"", $name, "\"\n";

返回

name = "Anton"
name = "Antonio"
null = ""
oops = ""
substr outside of string at substr.pl line 13.