bash脚本中$符号的具体使用

name="world"
echo "Hello, $name"

echo "Script name: $0"
echo "First argument: $1"
echo "Number of arguments: $#"

grep "text" file.txt
if [ $? -eq 0 ]; then
    echo "Text found."
else
    echo "Text not found."
fi

num1=5
num2=3
sum=$((num1 + num2))
echo $sum  # 输出 8

files=$(ls)
echo "Files in directory: $files"

greeting="hello"
echo "$greeting world"
echo '$greeting world'

greeting="world"
echo "Hello, ${greeting}ly"  # 会输出 Hello, worldly

str="abcdefghijk"
echo "${str:3:4}"  # 从索引3开始提取长度为4的子字符串，输出 "defg"

echo "${unset_var:-default_value}"  # 如果变量 unset_var 没有设置，输出 "default_value"

filepath="/path/to/your/file"
echo "${filepath/to/from}"  # 替换第一个匹配的 "to"，输出 "/path/from/your/file"
echo "${filepath//to/from}"  # 替换所有匹配的 "to"，输出 "/path/from/your/file"

array=(one two three)
echo "${array[1]}"  # 输出 "two"

mystring="hello world"
echo "${#mystring}"  # 输出字符串长度 "11"

filename="myfile.txt"
echo "${filename%.*}"  # 删除最短匹配 . 及其后面的内容，输出 "myfile"
echo "${filename%%.*}"  # 删除最长匹配 . 及其后面的内容，输出 "myfile"