In this method, I will be using the-nflag to check whether the variable is empty or not. Here's the simple script which will tell me whether the variable is empty or non-empty: #!/bin/bash variable="" if [ -n "$variable" ]; then echo "Variable is not empty." else echo "Vari...
Use the if-else statement with the -v option to check if an environment variable is set in bash. The echo command in the if block will be executed if the will
variable=$'这是第一行\n这是第二行' 这样,变量"variable"的值也将包含两行文本,通过"\n"进行换行。 需要注意的是,在使用这些方法时,需要确保脚本中的换行符在输出时能够被正确解释。可以使用echo命令来输出变量的值,并使用-e选项来解释转义字符。例如: 代码语言:txt 复制 echo -e $variable 这样,将会按照...
the variable X is not the empty string 为何?这是因为shell将$X展开为空字符串,表达式[-n]返回真值(因为改表达式没有提供参数)。再看这个脚本: 1 2 3 4 5 #!/bin/bash X="" if[ -n"$X"];then# -n 用来检查变量是否非空 echo"the variable X is not the empty string" fi 在这个例子中,表...
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...
“if-else” statement within the square brackets. This option is checking whether the length of variable “val” is other than zero or not. If the length of variable “val” is other than zero, the “-n” option will return true, and the “then” part of the statement will get ...
/bin/bash## Name: test-bucket-1## Purpose:# Performs the test-bucket number 1 for Product X.# (Actually, this is a sample shell script,# which invokes some system commands# to illustrate how to construct a Bash script)## Notes:# 1) The environment variable TEST_VAR must be set# (...
[ false ] # 'false' being true if ( -f file ) # Using (..) instead of test Style ShellCheck can make suggestions to improve style: [[ -z $(find /tmp | grep mpg) ]]# Use grep -q insteada >>log; b >>log; c >>log# Use a redirection block insteadecho"The time is `date...
從 shell 的角度來看,一個變量 variable 是一個由名稱 name 代表的參數。一個 變量有一個值 value 以及零個或多個屬性 attibutes。屬性可以使用內建命令 declare 來設置(參見下面 shell 內建 命令(SHELL BUILTIN COMMANDS) 章節中對 declare 的描述)。 如果給一個參數賦值,那麼它就被定義了。空字符串是有效...
complete-variable (M-$) 嘗試對 point 之前的文本進行補全,將它視爲 shell 變量。 possible-variable-completions (C-x $) 列出point 之前的文本可能的補全,將它視爲 shell 變量。 complete-hostname (M-@) 嘗試對 point 之前的文本進行補全,將它視爲主機名。 possible-hostname-completions (C-x @) 列出...