Use the if-else statement with the -v option to check if an environment variable is set in bash. The echo command in the if block will be executed if the will
/test.sh var is unsetvar is set to '123' 如果我在If块中检查未设置的变量,检查就会起作用但是,在for循环中,if块仅在设置了变量时才打印,而不是在未设置变量时打 浏览12提问于2017-06-21得票数3 回答已采纳 2回答 BASH检查变量中是否存在 、、、 但是,如果机器有特定的IP地址,我们只想尝试映射驱动器...
if [ -z "$var" ]; then echo "var is unset"; else echo "var is set to '$var'"; fi This is because it doesn't distinguish between a variable that is unset and a variable that is set to the empty string. That is to say, ifvar='', then the above solution will incorrectly ou...
{ echo "hahh" echo "lalal" } > /tmp/test 5、判断变量是否存在或为空 代码语言:javascript 复制 if [ -z ${var+x} ]; then echo "var is unset"; else echo "var is set to '$var'"; fi 参考:https://stackoverflow.com/questions/3601515/how-to-check-if-a-variable-is-set-in-bash...
typeset-Fr EPOCHREALTIME 条件判断 Conditional Constructs/GNU 拖入浏览器,方可跳转到指定锚点https://www.gnu.org/software/bash/manual/bash.html#:~:text=%5D-,3.2.5.2%20Conditional%20Constructs,-if Shell 中test单中括号[\] 双中括号[[]]
test的判断表达式分为4类 string integer expression file testexits with the status determined by EXPRESSION. Placing the EXPRESSION between square brackets ([and]) is the same as testing the EXPRESSION withtest. To see the exit status at the command prompt, ...
Why is printf better than echo? How to check if a variable is set in Bash? SettingIFSfor a single statement readarray(akamapfile) issue Tools Match command-line arguments to their help text Bash/Tcsh Comparison Table Collections of scripts ...
>>> core__bash_version_test=true >>> core_is_defined undefined_variable; echo $? 1>>> core__bash_version_test=true >>> set -o nounset >>> core_is_defined undefined_variable; echo $? 1Function core_is_emptyTests if variable is empty (undefined variables are not empty)>>> local ...
[ian@pinguino ~]$ set -u [ian@pinguino ~]$ test -o nounset; echo $? 0 1. 2. 3. 4. 5. 6. 最后,-a和-o选项允许使用逻辑运算符 AND 和 OR 将表达式组合在一起。单目操作符!可以使测试的意义相反。可以用括号把表达式分组,覆盖默认的优先级。请记住 shell 通常要在子 shell 中运行括号中的...
如果if结构使用的不是test命令,而是普通命令,比如上一节的((...))算术运算,或者test命令与普通命令混用,那么可以使用 Bash 的命令控制操作符&&(AND)和||(OR),进行多个命令的逻辑运算。$ command1 && command2 $ command1 || command2对于&&操作符,先执行command1,只有command1执行成功后, 才会执行command2。