Shell字符串操作完全指南

# 使用 ${#VAR}
VAR="hello"
echo ${#VAR}
# 输出: 5

# 变量也可以直接
echo ${#"hello"}
# 输出: 5

# Bash
VAR="hello"
echo ${#VAR}        # 5
echo ${#VAR[0]}     # 数组

# expr 命令
VAR="hello"
expr length "$VAR"
# 输出: 5

# wc 命令
VAR="hello"
echo -n "$VAR" | wc -c
# 输出: 5

# awk
VAR="hello"
echo "$VAR" | awk '{print length}'
# 输出: 5

VAR="Hello World"

# ${VAR:start} - 从第start个字符截取到结尾（从0开始）
echo ${VAR:1}
# 输出: ello World

# ${VAR:start:length} - 截取从start开始，长度为length的字符
echo ${VAR:0:5}
# 输出: Hello

# ${VAR: -length} - 从右边截取length个字符（注意冒号后有空格）
echo ${VAR: -5}
# 输出: World

VAR="Hello World"

# expr substr $VAR start length
expr substr "$VAR" 1 5
# 输出: Hello

# start从1开始

VAR="Hello World"

# 截取前5个字符
echo "$VAR" | cut -c1-5
# 输出: Hello

# 截取第7个字符到最后
echo "$VAR" | cut -c7-
# 输出: World

VAR="Hello World World"

# ${VAR/pattern/replacement}
echo ${VAR/World/Shell}
# 输出: Hello Shell World

VAR="Hello World World"

# ${VAR//pattern/replacement}
echo ${VAR//World/Shell}
# 输出: Hello Shell Shell

VAR="Hello World"

# 替换开头的匹配
echo ${VAR/#Hello/Hi}
# 输出: Hi World

# 替换结尾的匹配
echo ${VAR/%World/Earth}
# 输出: Hello Earth

VAR="Hello World"

# 删除第一个匹配
echo ${VAR/World}
# 输出: Hello 

# 删除所有匹配
echo ${VAR//World}
# 输出: Hello 

# 删除开头匹配
echo ${VAR/#Hello}
# 输出:  World

# 删除结尾匹配
echo ${VAR/%World}
# 输出: Hello 

VAR="/path/to/file.txt"

# 删除最小的前缀匹配
echo ${VAR##*/}
# 输出: file.txt

# 删除最大的前缀匹配（##贪婪匹配）
echo ${VAR##*/}
# 输出: file.txt

# 删除最小的后缀匹配
echo ${VAR%.*}
# 输出: /path/to/file

# 删除最大的后缀匹配
echo ${VAR%%.*}
# 输出: /path/to

# 获取文件名
FILE="/var/log/nginx/access.log"
echo ${FILE##*/}
# 输出: access.log

# 获取目录
FILE="/var/log/nginx/access.log"
echo ${FILE%/*}
# 输出: /var/log/nginx

# 获取扩展名
FILE="document.pdf"
echo ${FILE##*.}
# 输出: pdf

# 去除扩展名
FILE="document.pdf"
echo ${FILE%.*}
# 输出: document

# 判断是否为空
VAR=""
if [ -z "$VAR" ]; then
    echo "VAR is empty"
fi

# 判断是否非空
VAR="hello"
if [ -n "$VAR" ]; then
    echo "VAR is not empty"
fi

# 判断是否相等
VAR1="hello"
VAR2="hello"
if [ "$VAR1" = "$VAR2" ]; then
    echo "equal"
fi

VAR="Hello World"

# 转换为大写
echo ${VAR^^}
# 输出: HELLO WORLD

# 转换为小写
echo ${VAR,,}
# 输出: hello world

# 直接连接
VAR1="Hello"
VAR2="World"
VAR3="$VAR1 $VAR2"
echo $VAR3
# 输出: Hello World

# 去除文件名中的空格
for file in *\ *; do
    mv "$file" ${file// /_}
done

URL="https://www.example.com/path/to/page"

# 方法1：删除协议和路径
DOMAIN=${URL#*://}
DOMAIN=${DOMAIN%%/*}
echo $DOMAIN
# 输出: www.example.com

DATE=$(date +%Y%m%d)
FILENAME="backup_$DATE.tar.gz"
echo $FILENAME
# 输出: backup_20260314.tar.gz

VAR="Hello World"

if [[ "$VAR" == *"World"* ]]; then
    echo "包含 World"
fi