Perl 程式設計/關鍵字/substr

Thesubstrkeyword

Thesubstr命令從EXPRESSION中提取並返回子字串，其中第一個字元位於OFFSET 0處。如果OFFSET為負數，則從字串末尾開始計數。如果LENGTH為負數，則從字串末尾保留這麼多字元。

substr也可以用作左值，如果EXPRESSION也是左值。透過分配大於或小於LENGTH的字串，字串將分別增長或縮小以容納它。

如果OFFSET和LENGTH指定的子字串部分位於字串外部，則僅返回字串內的部分。如果它超出了兩端，則返回 undef，如果它是一個左值，則會丟擲異常。

語法

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

示例

程式碼

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.