The-zoperator returnstrueif a string variable is null or empty. How the use the-zBash Operator Afterdeclaring a string variable, use the-zoperator in anif statementto check whether a string is empty or not: MY_STRING="" if [ -z $MYSTRING ] then echo "String is empty" else echo "...
-n is one of the supported bash string comparison operators used for checking null strings in a bash script. When -n operator is used, it returns true for every case, but that’s if the string contains characters. On the other hand, if the string is empty, it won’t return true. -...
#文件测试操作-d FILE_NAM # TrueifFILE_NAM is a directory-e FILE_NAM # TrueifFILE_NAM exists-f FILE_NAM # TrueifFILE_NAM existsandis a regular file-r FILE_NAM # TrueifFILE_NAM is readable-s FILE_NAM # TrueifFILE_NAM existsandisnotempty...
# 每一句指令以换行或分号隔开：echo 'This is the first line'; echo 'This is the second line'# 声明一个变量：Variable="Some string"# 下面是错误的做法：Variable = "Some string"# Bash 会把 Variable 当做一个指令，由于找不到该指令，因此这里会报错。# 也不可以这样：Variable= 'Some string'# ...
There is NO WARRANTY, to the extent permitted by law. 回声,以及为什么你应该避免它 当我开始编写 shell 脚本时,我很快就了解了 Unix 的两个主要分支:美国电话电报公司的 System V 和 BSD 。他们的不同之处之一是echo的行为。所有现代 shells 中的一个内部命令,echo将其参数打印到标准输出流中,参数之间...
string1 != string2 若两个字符串不相等,则为真 int1 -eq int2 若int1等于int2,则为真 int1 -ne int2 若int1不等于int2,则为真 int1 -lt int2 若int1小于int2,则为真 int1 -le int2 若int1小于等于int2,则为真 int1 -gt int2 若int1大于int2,则为真 ...
How to check if a variable exists or is “null”? How to check if a file exists? How to check if a directory exists? How to check if a command succeeds or failed? How to do string comparison and check if a string equals to a value? How to check if a string is in an array?
is greater than or equal to -lt is less than -le is less than or equal to String Operators Operators Explanation = is equal to == is equal to != is not equal to < less than <= is less than or equal to > greater than >= is greater than or equal to -z string is null -n ...
4-4. 整型还是string?4-5. 位置参数4-6. wh,whois节点名字查询4-7. 使用shift5-1. echo一些诡异的变量5-2. 转义符6-1. exit/exit状态6-2. 否定一个条件使用!7-1. 什么情况下为真?7-2. 几个等效命令test,/usr/bin/test,[],和/usr/bin/[7-3. 算数测试使用(( ))7-4. test死的链接文件...
和">"可用来做 整数比较操作. 参见例子 12-9. << 用在here document中的重定向. <<< 用在here string中的重定向. <, > ASCII comparison. 1 veg1=carrots 2 veg2=tomatoes 3 4 if [[ "$veg1" < "$veg2" ]] 5 then 6 echo "Although $veg1 precede $veg2 in the ...