perl uc,lc,ucfirst,lcfirst大小写转换函数

Perl 提供了四个主要的大小写转换函数：

1. uc - 转换为大写

my $text = "hello world";
my $upper = uc($text);  # "HELLO WORLD"
print uc("perl");       # "PERL"

2. lc - 转换为小写

my $text = "HELLO WORLD";
my $lower = lc($text);  # "hello world"
print lc("Perl");       # "perl"

3. ucfirst - 首字母大写

my $text = "hello";
my $capitalized = ucfirst($text);  # "Hello"
print ucfirst("perl programming");  # "Perl programming"

4. lcfirst - 首字母小写

my $text = "Hello";
my $lower_first = lcfirst($text);  # "hello"
print lcfirst("PERL");            # "pERL"

完整示例

#!/usr/bin/perl

my $text = "Hello Perl World";

print "原字符串: $text\n";
print "uc: " . uc($text) . "\n";          # HELLO PERL WORLD
print "lc: " . lc($text) . "\n";          # hello perl world
print "ucfirst: " . ucfirst($text) . "\n"; # Hello Perl World
print "lcfirst: " . lcfirst($text) . "\n"; # hello Perl World

# 处理非ASCII字符（需要开启utf8）
use utf8;
binmode STDOUT, ':encoding(utf8)';

my $unicode = "café naïve";
print "Unicode示例:\n";
print "uc: " . uc($unicode) . "\n";        # CAFÉ NAÏVE
print "lc: " . lc($unicode) . "\n";        # café naïve

实际应用场景

# 1. 规范化用户输入
my $username = "ADMIN";
my $normalized = lc($username);  # "admin"

# 2. 标题格式化
my $title = "the great gatsby";
$title = ucfirst($title);        # "The great gatsby"

# 3. 变量名转换
my $ClassName = "MyModule";
my $method_name = lcfirst($ClassName);  # "myModule"

# 4. 批量处理数组
my @words = ("apple", "BANANA", "Cherry");
my @lowercase = map { lc($_) } @words;  # ("apple", "banana", "cherry")
my @uppercase = map { uc($_) } @words;  # ("APPLE", "BANANA", "CHERRY")

注意事项

这些函数对非ASCII字符（如带重音符号的字符）的处理取决于Perl版本和编码设置对于现代Perl（5.16+），建议使用use feature 'unicode_strings'来获得更好的Unicode支持这些函数不会修改原始字符串，除非在标量上下文中赋值给原变量

修改原字符串的用法

my $string = "Original Text";
$string = uc($string);  # 修改原变量

# 或者使用函数返回值直接覆盖
$_ = "some text";
$_ = uc;  # uc在无参数时使用$_作为默认参数

这些函数是Perl字符串处理的基础工具，非常实用且高效。