利用判断符号[ ]
- [ str ] : str 字符串存在为真
1 [root@localhost ~]# if [ ]; then echo 'true';else echo 'false';fi 2 false 3 [root@localhost ~]# 4 [root@localhost ~]# if [ 123 ]; then echo 'true';else echo 'false';fi 5 true 6 [root@localhost ~]# if [ ]; then echo 'true';else echo 'false';fi 7 false 8 [root@localhost ~]# 9 [root@localhost ~]# if [ '123' ]; then echo 'true';else echo 'false';fi 10 true 11 [root@localhost ~]# 12 [root@localhost ~]# if [[ '123' ]]; then echo 'true';else echo 'false';fi 13 true 14 [root@localhost ~]# 15 [root@localhost ~]# if [[ '' ]]; then echo 'true';else echo 'false';fi 16 false
- -n : nozero 字符串长度不为0时为真
- -z: zero 字符串长度为0时为真
1 [root@localhost ~]# a=123 2 [root@localhost ~]# 3 [root@localhost ~]# if [[ -n $a ]]; then echo 'true';else echo 'false';fi 4 true 5 [root@localhost ~]# 6 [root@localhost ~]# if [ -n $a ]; then echo 'true';else echo 'false';fi 7 true 8 [root@localhost ~]# 9 [root@localhost ~]# if [ -z $a ]; then echo 'true';else echo 'false';fi 10 false 11 [root@localhost ~]# a= 12 [root@localhost ~]# 13 [root@localhost ~]# if [ -z $a ]; then echo 'true';else echo 'false';fi 14 true 15 [root@localhost ~]# if [ -n $a ]; then echo 'true';else echo 'false';fi 16 true 17 [root@localhost ~]# 18 [root@localhost ~]# if [ -n "$a" ]; then echo 'true';else echo 'false';fi 19 false
循环体
1. for...do...done（固定循环）
for var in list do commands done
1. 示例1
#!/bin/bash for animal in dog cat elephant do echo "There are ${animal}s.." done
1 #!/bin/bash 2 for animal in dog cat elephant 3 do 4 echo "There are ${animal}s.." 5 done
1 #!/bin/bash 2 for((i = 0; i < 5; ++i)) 3 do 4 echo "this is test!" 5 done
产生十个随机数字
方法1：
#!/bin/bash for i in $(seq 10); do echo "$i: $RANDOM"; done
方法2：
1 #!/bin/bash 2 for((i = 0; i < 5; ++i)) 3 do 4 echo "this is test!" 5 done