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 [-v HOME] will be true, and it will be true if the speci
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 6、换算秒为分钟、小时 代码语言:javascript 代码运行次数:0 运行 AI代码解释 #!/bin/bash a=60100 sw...
# 取消变量的值 unset my_variable 还可以使用环境变量为变量赋值。例如,可以使用$PATH环境变量: 代码语言:txt 复制 # 使用环境变量为变量赋值 current_path=$PATH echo "当前的PATH环境变量值为:$current_path" 参考链接: Bash变量赋值 相关搜索: linux bash 变量赋值 在bash中赋值位置变量 如何为bash中的布尔值...
-bash: a: unbound variable 条件判断 虽然你可以通过上面的测试和&&、||控制操作符来完成一个大量的程序设计,不过bash环境中还包含了更亲切的“if,then,else”和case语法结构。当你学会了这两种结构之后,你还会学到循环结构,这时你的知识结构才会真正拓展开来。 if-then-else语句 bash环境下的if命令是一个复合的...
{var}" --->2 - Value of var is Variable is not setunset var --->删除了var的赋值echo${var:+"This is default value"} --->由于var未赋值,此行不打印echo"3 - Value of var is $var" --->3 - Value of var isvar="Prefix" --->var已赋值为Prefixecho${var:+"This is default ...
#!/bin/bash # Set the variable variable="" # Check if the variable is empty if [ -z "$variable" ]; then echo "Variable is empty." else echo "Variable is not empty." fi Copy Save changes and exit from the nano text editor. Finally, use the chmod command to make the file execut...
is a ! or a ^ then any character not enclosed is matched. The sorting order of characters in range expressions is determined by the current locale and the value of the LC_COLLATE shell variable, if set. A - may be matched by including it as the first or last character in the set. ...
cp is /usr/bin/cp $$变量的继承:除了直接执行bash命令和shell脚本这两种子shell,其他进入子shell的情况都会继承父shell的值 无论是使用export还是source,环境设置都只能从父shell到子shell,不是也不会是从子shell到父shell。也就是说子shell的变量等不会影响父shell read read [-options] [variable...] echo...
VARIABLE=2 然后我们通过 $VARIABLE 引用该变量。这里有一点非常重要，也极容易忽视的就是：千万不要在等号两边加空格。虽然加上空格也不会引起语法错误，但很可能造成意想不到的结果。例如 VARIABLE= 2 这个语句，解释器很可能会将一个空字符串赋值给 VARIABLE，然后运行一个名字叫 2 的脚本。一般常用的 Bash ...
# set variable identifying the chroot you work in (used in the prompt below) if [ -z "${debian_chroot:-}" ] && [ -r /etc/debian_chroot ]; then debian_chroot=$(cat /etc/debian_chroot) fi # set a fancy prompt (non-color, unless we know we "want" color) ...