TestFile1 exists and contains data. 现在加入 elif 语句来辨别是文件不存在还是文件为空: [student@studentvm1 testdir]$ File="TestFile1" ; touch $File ; if [ -s $File ] ; then echo "$File exists and contains data." ; elif [ -e $File ] ; then echo "$File exists and is empty."...
逻辑操作符(logical operator)。 在测试结构中,可以用这两个操作符来进行连接两个逻辑值。 ||是当测试条件有一个为真时返回0(真),全假为假; &&是当测试条件两个都为真时返回真(0),有假为假。 43. - 减号 减号,连字符(Hyphen/minus/dash)。 \1. 作为选项,前缀[option, prefix]使用。用于命令或者过滤...
TestFile1 exists and is empty. [student@studentvm1 testdir]$ File="TestFile1" ; echo "This is $File" > $File ; if [ -s $File ] ; then echo "$File exists and contains data." ; elif [ -e $File ] ; then echo "$File exists and is empty." ; else echo "$File does not ...
https://bash.cyberciti.biz/guide/Logical_OR Logical OR ← Logical ANDHomeLogical Not ! → Logical OR (||) isboolean operator. It can execute commands orshell functionsbased on theexit statusof another command. Contents 1 Find username else display an error 1.2How Do I Combine Both Logical ...
Three types of logical operators can be used in the Bash conditional statement. These are logical OR (||), logical AND (&&), and logical NOT (!). A code value is taken from the user. If the input value is non-empty, the value is checked with two code values using logical OR. If...
Different types of logical conditions can be used in if statement with two or more conditions. How you can define multiple conditions in if statement using AND logic is shown in the following example. ‘&&’ is used to apply AND logic of if statement. Create a file named ‘if_with_AND....
Using the logical AND operator (&&) When you use the “&&” operator, you're instructing the system to run the second command only if the first command runs successfully. Thus, if the exit code of the first command doesn’t return “0”, then the second command won’t run. Example: ...
logical AND operator. | | logical OR operator. $# Used to expands the number of arguments passed to the script. $0 Used to expands to the name of the shell. $1, $2 Used as an input parameter that you can add when running script. exit [0-255] Used to exit the script and re...
The double-ampersand syntax is meant to be reminiscent of the logical AND operator in the C language.If you know your logic (and your C) then you’ll recall that if you are evaluating the logical expressionA AND B, the entire expression can only be true if both (sub)expressionAand (su...
!negates the next logical operation: $echohello&&echotesthellotest$echohello||echotesthello$!echohello||echotesthellotest You can use parentheses to combine expressions to avoid confusion, and also to change the precedence: $!(echohello)||(echotest)hellotest$!(echohello||echotest)hello ...