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
$ unset x $ showvar $x is not set $ x=3 $ showvar $x is not set $ export x $ showvar $x = 3 $ x= ## in bash, reassignment doesn't remove a variable from the environment $ showvar $x is set but empty 注意 showvar不是一个 bash 命令,而是一个如清单 5-1 所示的脚本,...
You can assign data to a variable using the equals sign (=). The data you store in a variable can either be a string or a number. Let’s create a variable now on the command line: chapter_number=5 The variable name is on the left hand side of the equals sign, and the data whic...
echo"the variable X is not the empty string" fi 运行这个脚本,输出如下: the variable X is not the empty string 为何?这是因为shell将$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"$X"];then# -n 用来检查变量是...
The proper way to handle errors is to check if the program finished successfully or not, using return codes. It sounds obvious but return codes, an integer number stored in bash$?or$!variable, have sometimes a broader meaning. Thebash man pagetells you: ...
How to write a bash script to set global environment variable? 最近我写了一个设置环境变量的脚本,看看: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 #!/bin/bash echo"Pass a path:" readpath echo$path defaultPath=/home/$(whoami)/Desktop ...
When bash is started non-interactively, to run a shell script, for example, it looks for the variable BASH_ENV in the environment, expands its value if it appears there, and uses the expanded value as the name of a file to read and execute. Bash behaves as if the following command ...
Theif [ -d $directory ]command can be used to check for the existence of a directory. If the specified directory exists, the command will return an exit status of0(true). If the directory does not exist, the command will return anon-zero exit status(false). ...
SHELL The full pathname to the shell is kept in this environment variable. If it is not set when the shell starts, bash assigns to it the full pathname of the current user’s login shell. TIMEFORMAT The value of this parameter is used as a format string specifying how the timing ...
👉 It’s often conveninent to define your debugging functions and trap in a separate source file and invoke it only when debugging using the bash environment variable $BASH_ENV. Find where a bash function is defined In many cases, it may be useful to find out where a function has been...