echo"Error: TARGET_DIR is not defined." exit1 fi # 试运行模式以确保安全 if[["${DRY_RUN:-false}"== "true"]]; then echo"Dry run: Listing files to delete in$TARGET_DIR" ls"$TARGET_DIR" else echo"Deleting files in$TARGET_DI
如果变量var未被定义或为空,则输出“Variable is either not defined or empty”,否则输出“Variable is defined and not empty”。 总的来说,在bash中判断一个变量是否为空或未被定义是非常简单的,只需要结合if语句和条件判断即可实现。通过合理地运用这些技巧,我们可以更加灵活地处理各种变量情况,从而编写出更加健...
if [[ ${x+X} = X ]] ## If $x is set then if [[ -n $x ]] ## if $x is not empty then printf " \$x = %s\n" "$x" else printf " \$x is set but empty\n" fi else printf " %s is not set\n" "\$x" fi 一旦变量被导出,它将一直保留在环境中,直到被取消设置: $...
```bash if [ -z "$b" -a "${bxxx}" = "xxx" ] # 这里的判断会有单独的文章介绍 then echo 'b is set but empty'; # 设置但为空 else echo 'b is not set'; # 没设置,如 c fi``` 变量中的空格 代码语言:javascript 代码运行次数:0 运行 AI代码解释 e=123# 报错,变量中间当然不能有...
If this variable is set and not null, its value is used as a format string for strftime(3) to print the time stamp associated with each history entry displayed by the history builtin. If this variable is set, time stamps are written to the history file...
a non-empty string (1)# $JAIL set to the empty string (2)# $JAIL can be unset (3)###echo "*** Current value of \$JAIL is '$JAIL' ($HINT) ***" ## Determine if a bash variable is empty or not ##if [ -z "${JAIL}" ]; then echo "JAIL is unset or set to the...
bash 中有四种类型的变量,它们是环境变量、本地变量、位置变量和特殊变量。...参考文章 bash shell学习之变量 Shell变量 How to tell if a string is not defined in a bash shell script? 1.1K30 Bash shell 中,select 使用举例 文章目录 Bash shell 中,select 使用举例一 背景二 使用举例 2.1 单独使用.....
This will execute the script and inform the shell of any functions or aliases defined for the current session. Note that this change will not persist across different terminal sessions, so you must run the ‘source’ or ‘.’ command again if you open a new terminal or restart your computer...
locale is not C or POSIX. This implies the -n option; no commands will be executed. [-+]O [shopt_option] shopt_option is one of the shell options accepted by the shopt builtin (see SHELL BUILTIN COMMANDS below). If shopt_option is present, -O sets the value of that ...
ShellCheck will warn when using features not supported by the shebang. For example, if you set the shebang to#!/bin/sh, ShellCheck will warn about portability issues similar tocheckbashisms: echo{1..$n}# Works in ksh, but not bash/dash/shecho{1..10}# Works in ksh and bash, but ...