One, variable
Environment variables, positional variables, pre-defined variables
1. Environment Variables
Env #查看环境变量
2. Position variable
VI location.sh
#!/bin/bash
sum= ' expr + $ '
echo "$ + $ = $SUM"
./location #则12为第一个位置变了 $1,32 changed the second position. Location is a predefined variable
3. Pre-defined variables
$##表示命令行中位置参数的个数
$*#表示所有位置参数的内容
$?#表示执行后的返回状态, 0 is normal.
$#表示当前执行的脚本或程序名称
VI yu.sh
#!/bin/bash
name=bak-' Date +%y%m%d '. tar.gz
Tar zcf $name $* & >/dev/null
echo "Execute $ script"
echo "Complete $# object"
echo "Content is $*"
=========================================================================================
second, condition test operation []
1. File Test
-D #判断是否为directory [-d/etc] && echo "This is a directory"
-E#判断是否exist[-e/var/log/messages] && echo "exist"
-F #判断是否为file[-F/ETC/PASSWD] && echo "This is a file"
-R #判断是否有read[-R Read] && echo "Premission is a read"
-W #判断是否有write[w write] && echo "Premission is a write"
-X #判断是否有execute[-X Execute] && ECHP "Premission is a execute"
-L #判断是否为link
-B #判断是否为black[-b/dev/sr0] && echo "This is a block"
-C #判断是否为chatset[-C/DEV/VCSA] && echo "This is a charset"
2, integer value comparison
-eq #1等于2
-ne #1不等于2
-gt #1大于2
-lt #1小于2
-ge #1大于或等于2
-le #1小于或等于2
User= ' who | Wc-l ' # $user to 3
[$user-lt 4] && echo Yes
3. String comparison
=#第一个字符串等于第二个字符串
!= #第一个字符串不等于第二个字符串
-Z #检查字符串是否为空, a variable that is not defined or given a null value is treated as an empty string
[$LANG = en_US. UTF-8] && echo Yes
4. Logic Test
&& # "Plus", the return value of the entire test command is 0 when both the current face and the next two conditions are true
|| # "Logical OR", as long as one of the preceding and subsequent two conditions is established, the return value of the entire test command is 0
! # "Logical No", the return value of the entire test command is 0 only if the specified condition is not true
[$LANG! = zh_cn. UTF-8] && [$user! =] && echo Yes # # $user =3
[$LANG! = zh_cn. UTF-8] | | [$user! = 3] && echo Yes
A summary of---variables, comparisons, and tests used in shell programming
