-bash: syntax error in conditional expression -bash: syntax error near 'on' 可以看到,将value变量值设成空,[[ -n $value ]]返回为 1,确认该变量值不为空是 false。 [[ -z $value ]]返回为 0,确认该变量值为空是 true。 即使$value不加双引号,也能正确判断。 如果是用[命令就会判断异常。 当value变量值包含空格时,[[ -n $...
-bash: syntax error in conditional expression -bash: syntax error near 'string' 可以看到,value变量对应的字符串带有空格,[[ -n $value ]]命令可以正确判断到value变量值不是空字符串,没有对该变量值进行单词拆分。 而test -n $value命令会执行报错,value变量值带有空格,$value经过单词拆分后会变成两个字符...
[root@seker ~]# [[ a = a -a 10 < 20 ]] bash: syntax error in conditional expression -bash: syntax error near `-a' [root@seker ~]# [[ a = a && 10 < 20 ]] [root@seker ~]# echo $? 0 [root@seker ~]# [[ a = a || 10 < 20 ]] [root@seker ~]# echo $? 0 [...
for ip in 192.168.1.{1..255} ;do ping ${ip} -w 1 &> /dev/null && echo ${ip} is Alive;done for ip in `cat iplist`;do scp config/${ip}.conf $ip:/home/shell/;done for x in `cat 1.txt`; do echo $x;mkdir dir{0..2}{0..2}_$x; done for i in `cat iplistr....
bash: syntax error in conditional expression bash: syntax error near `-o' #注:[[ ]] 剔除了 test 命令的-o和-a选项,你只能使用 || 和 &&。但可以写成如下格式: [root@localhost tmp]# [[ -z $str1 ]] || [[ -z $str2 ]]
-bash: syntax error in conditional expression -bash: syntax error near `-a' [root@seker ~]# [[ a = a && 10 < 20 ]] [root@seker ~]# echo $? 0 [root@seker ~]# [[ a = a || 10 < 20 ]] [root@seker ~]# echo $?
Place the jobs identified by each JOB_SPEC in the background, as if they had been started with `&'. If JOB_SPEC is not present, the shell's notion of the current job is used. Exit Status: Returns success unless job control is not enabled or an error occurs. ...
It receives events and, based on those events, runs jobs that can in turn produce more events, causing Upstart to run more jobs, and so on. systemd是目标导向的。你定义一个目标,以及它的依赖关系和你想要达到目标的时间。systemd满足依赖关系并解决目标。systemd还可以推迟启动服务,直到绝对需要时再...
You can use MERGE to write conditional SQL statements that can include the INSERT, UPDATE, and DELETE actions in a single statement. PostgreSQL provides the following new functions for using regular expressions to inspect strings: regexp_count(), regexp_instr(), regexp_like(), and ...
The conditional ends with esac. 脚本将$1与用字符)分隔的每个case值进行匹配。 如果一个case值与$1匹配,shell将执行case下面的命令,直到遇到;;,然后跳转到esac关键字。 条件以esac结束。 For each case value, you can match a single string (like bye in the preceding example) or multiple strings with...