变量
变量定义
var="hello"
echo $var ${var}-name
位置参数
| param |
desc |
| $0 |
script file |
| $1 .. $n |
script params |
| $# |
param count |
| $@ $* |
all params |
| $? |
most recent ret code |
| $! |
most recent background job pid |
$@ vs $*
# script.sh
function main() {
echo 'I got ' $# ' args'
}
main $*
main $@
main "$*"
main "$@"
# output
$ sh script.sh 'a b c' d e
I got 5 args
I got 5 args
I got 1 args
I got 3 args
条件控制
注意项
-
[ -z "" ] 前后都有空格
-
[ "1" \> "" ] 因为 [ 是命令，后面跟着的都是它的参数，所以不要少加空格，且为了防止 > 被解析为重定向符号要转义
-
[[ "1" > "" ]] 因为 [[ ]] 是 bash 的语法结构，所以不需要转义
逻辑测试
| param |
desc |
| (e) |
([ -n "hello" ]) |
| not e |
[ ! -n "hello" ] 等价于 ! [ -n "" ] |
| e1 and e2 |
[ -n "" -a -n "" ] 等价于 [ -n "" ] && [ -n "" ] |
| e1 or e2 |
[ -n "" -o -n "" ] 等价于 [ -n "" ] |
|
[ -n "" ] |
文件测试
| param |
desc |
| -d FILE |
is directory |
| -f FILE |
is file |
| -e FILE |
file or dir exists |
| -x FILE |
excutable |
| f1 -nt f2 |
f1 newer then f2 |
| f1 -ot f2 |
f1 older then f2 |
| ... |
man test |
字符串测试
| param |
desc |
| -z str |
len(str) == 0 |
| -n str |
len(str) > 0 |
| s1 = s2 |
s1 == s2 |
| s1 != s2 |
s1 != s2 |
| s1 > s2 |
s1 > s2 |
| !(s1 < s2) |
s1 >= s2 |
| s1 < s2 |
s1 < s2 |
| !(s1 > s2) |
s1 <= s2 |
| ... |
man test |
数字测试
| param |
desc |
| n1 -eq n2 |
algebraically == |
| n1 -ne n2 |
algebraically != |
| n1 -gt n2 |
algebraically > |
| n1 -ge n2 |
algebraically >= |
| n1 -lt n2 |
algebraically < |
| n1 -le n2 |
algebraically <= |
| ... |
man test |
直接测试
$ test expression && echo yes
$ [ expression ] && echo yes
$ [[ expression ]] && echo yes
条件判断
if [[ expression ]]; then
# ...
elif [[ expression ]]; then
# ...
else
# ...
fi
条件选择
case VAR in
var1) cmd1 ;;
var2) cmd2 ;;
# ...
*) cmd ;;
esac
循环控制
for
for var in (list); do
# ...
break
continue
done
for ((i=1, j=10; i <= 10; i++, j--)); do
# ...
done
while
while ((1)); do
# ...
break
continue
done
while true; do
# ...
done
until
until [[ -n "" ]]; do
# ...
break
continue
done
select DAY in Mon Tue Wed Thu Fri Sat Sun; do
case $DAY in
Mon) echo "Today is Monday" ;;
Tue) echo "Today is Tuesday" ;;
# ...
*) echo "Unkown day, stop" && break ;;
esac
done
# 函数
```shell
function foo() {
local var=0
return $var
}
