if [ -z "$variable" ]; then echo "variable is not set" fi 在上面的示例中,我们使用-z操作符检查$variable是否被设置。如果变量未设置,则执行echo语句。 检查变量是否被设置并且非空 我们可以使用-n操作符和$variable的值来检查变量是否被设置并且非空。下面是一个示例: ...
command, not just those that precede thecommandname.-mJob control is enabled.-nRead commands butdonot execute them.-ooption-name Set the variable corresponding to option-name: allexport same as-abraceexpand same as-Bemacs use an emacs-style line editing interface errexit same as-eerrtrace sam...
tered, an attemptismadetodefine afunctionusing``-f foo=bar'', an attempt is made to assign avaluetoareadonlyvariable, an attemptismadetoassign a valuetoan array variable withoutusingthe compound assignment syntax (see Arrays above), oneofthe namesisnota valid shell variable name, an attempti...
if [[ ! -v var ]]; then echo "Variable is not set" elif [[ -z "$var" ]]; then echo "Variable is set to the empty string" else echo "Variable has the value: $var" fi OUTPUT 1 2 3 Variable has the value: /root Use the if-else statement with the -n option to check...
Read and execute commands from filename in the current shell environment and return the exit status of the last command executed from filename.The return status is the status of the last command exited within the script (0 if no commands are executed), and false if filename is not found ...
13echo"If you are reading this messags"14echo"critical environmental vatiables have benn set"15echo16echo17#例2:#[variable?] 结构也能检查脚本中变量的设置情况18ThisVariable=Value-of-ThisVariable19:"Variable of ThisVaiable is $ThisVariable"20echo21echo22: ${SF?"SF ha not been set."}23#...
if [ "$?" -ne 0 ]; then echo "cmd failed";exit 1;fi # 写法四 命令1 && 命令2 上面那种常规方法,写法比较麻烦,所以set -e 参数解决了这一烦恼 #!/usr/bash set -e var echo "hello world" 执行上面脚本,结果如下 test: line 5: var: command not found ...
calls .envrc-kubernetes to set the kubectl context isolated to current shell to prevent race conditions between shells and scripts caused by otherwise naively changing the global ~/.kube/config context aws_sso_ssh.sh - launches local AWS SSO authentication pop-up (if not already authenticated),...
A. If yourcommand_not_found_handlefunction is not intended to address (possibly missing) commands invoked during bash programmable completion functions, you can account for this in the function by, for example, testing if the$COMP_LINEvariable is set and taking appropriate action, typically returni...
if [[ ! $var ]]; then ... # `$var' expands to the empty string (set or not) To see if a variable is set (empty or nonempty), I use if [[ ${var+x} ]]; then ... # `var' exists (empty or nonempty) if [[ ${1+x} ]]; then ... # Parameter 1 exists (empty o...