基础

echo 与导航

echo "Hello, World!"     # print text
pwd                      # print working directory
cd /path/to/dir          # change directory
cd ..                    # go up one level
cd ~                     # go to home directory
cd -                     # go to previous directory

列出与创建

ls                # list files
ls -la            # long format, show hidden
ls -lh            # human-readable sizes
mkdir mydir       # create directory
mkdir -p a/b/c    # create nested directories

复制、移动与删除

cp file.txt copy.txt      # copy file
cp -r dir/ backup/        # copy directory recursively
mv old.txt new.txt        # rename / move
rm file.txt               # delete file
rm -r dir/                # delete directory recursively
rm -rf dir/               # force delete (no prompt)

变量与展开

变量

name="Alice"              # assign (no spaces!)
echo "$name"              # variable expansion
echo "${name}_file"       # braces for clarity
readonly PI=3.14          # constant
unset name                # delete variable

特殊变量

$0	脚本名称
$1 $2 ...	位置参数
$#	参数个数
$@	所有参数（各自独立）
$*	所有参数（单个字符串）
$?	上条命令的退出状态
$$	当前进程 ID
$!	最后一个后台进程的 PID

命令替换与算术

files=$(ls)               # capture output
today=$(date +%Y-%m-%d)   # command substitution
count=$((5 + 3))          # arithmetic: 8
echo $((10 / 3))          # integer division: 3
echo $((10 % 3))          # modulo: 1

字符串操作

${#str}	字符串长度
${str:0:5}	子串（偏移量：长度）
${str/old/new}	替换第一个匹配
${str//old/new}	替换所有匹配
${str^^}	转大写
${str,,}	转小写

条件判断

if / elif / else

if [[ "$name" == "Alice" ]]; then
    echo "Hi Alice"
elif [[ "$name" == "Bob" ]]; then
    echo "Hi Bob"
else
    echo "Who are you?"
fi

测试运算符

-eq -ne	整数等于 / 不等于
-lt -gt	整数小于 / 大于
-le -ge	整数小于等于 / 大于等于
== !=	字符串等于 / 不等于
-z "$str"	字符串为空
-n "$str"	字符串非空
-f file	文件存在且为普通文件
-d dir	目录存在
-e path	路径存在（任意类型）
-r -w -x	可读 / 可写 / 可执行
&& \|\|	逻辑与 / 或

循环

for 循环

for fruit in apple banana cherry; do
    echo "$fruit"
done

for f in *.txt; do
    echo "File: $f"
done

C 风格 for 循环

for ((i=0; i<5; i++)); do
    echo "$i"
done

while 循环

count=0
while [[ $count -lt 5 ]]; do
    echo "$count"
    ((count++))
done

循环控制

break	退出循环
continue	跳到下一次迭代

函数

定义与调用

greet() {
    echo "Hello, $1!"   # $1 = first arg
    return 0             # exit status
}
greet "Alice"            # Hello, Alice!

局部变量与返回值

add() {
    local sum=$(($1 + $2))
    echo "$sum"          # "return" via stdout
}
result=$(add 3 5)        # capture: 8

管道与重定向

管道

ls -l | grep ".txt"      # pipe output
cat log | sort | uniq    # chain commands
cmd1 | tee out.txt       # pipe + save to file

重定向

cmd > file	重定向 stdout（覆盖）
cmd >> file	重定向 stdout（追加）
cmd < file	从文件重定向 stdin
cmd 2> file	重定向 stderr
cmd 2>&1	将 stderr 重定向到 stdout
cmd &> file	重定向 stdout + stderr
cmd << EOF	Here document（内联输入）
/dev/null	丢弃输出：`cmd > /dev/null`

文件操作

查看文件

cat file.txt             # print entire file
head -n 10 file.txt      # first 10 lines
tail -n 10 file.txt      # last 10 lines
tail -f log.txt          # follow (live updates)
less file.txt            # paginated viewer

统计与查找

wc -l file.txt           # count lines
wc -w file.txt           # count words
wc -c file.txt           # count bytes
find . -name "*.txt"     # find by name
find . -type d           # find directories
find . -mtime -7         # modified in last 7 days

其他文件命令

touch file	创建文件 / 更新时间戳
stat file	文件元数据（大小、日期）
file img.png	检测文件类型
diff a.txt b.txt	对比两个文件
sort file.txt	按行排序
uniq	去除相邻重复行
cut -d: -f1	按分隔符提取字段
tr 'a-z' 'A-Z'	字符转换 / 替换

文本处理

grep

grep "error" log.txt       # search for pattern
grep -i "error" log.txt    # case-insensitive
grep -r "TODO" src/        # recursive search
grep -n "func" file.go     # show line numbers
grep -c "error" log.txt    # count matches
grep -v "debug" log.txt    # invert match

sed

sed 's/old/new/' file      # replace first per line
sed 's/old/new/g' file     # replace all
sed -i 's/old/new/g' file  # edit in place
sed -n '5,10p' file        # print lines 5-10
sed '/pattern/d' file      # delete matching lines

awk

awk '{print $1}' file      # print first field
awk -F: '{print $1}' file  # custom delimiter
awk '$3 > 100' file        # filter by field value
awk '{sum+=$1} END{print sum}' file  # sum column

权限

chmod

chmod 755 script.sh    # rwxr-xr-x
chmod +x script.sh     # add execute
chmod -w file.txt      # remove write
chmod u+x,g-w file     # user +exec, group -write

权限参考

r (4)	读
w (2)	写
x (1)	执行
u / g / o	所有者 / 组 / 其他
755	所有者：rwx，组/其他：r-x
644	所有者：rw-，组/其他：r--

所有权

chown user file.txt         # change owner
chown user:group file.txt   # change owner + group
chown -R user:group dir/    # recursive

BASH 快速参考