【Linux】Pass arguments into a function（一）https://developer.aliyun.com/article/1395339
FUNCNAME in action
Create a shell script called funcback.sh:
创建名为 funcback.sh 的 shell 脚本：
#!/bin/bash # funcback.sh : Use $FUNCNAME backup(){ local d="$1" [[ -z $d ]] && { echo "${FUNCNAME}(): directory name not specified"; exit 1; } echo "Starting backup..." } backup $1
Save and close the file. Run it as follows:
保存并关闭文件。按以下步骤运行：
chmod +x funcback.sh funcback.sh /home funcback.sh
Sample outputs:
样本输出：
backup(): directory name not specified
Return values
返回值
It is possible to pass a value from the function back to the bash using the return command. The return statement terminates the function. The syntax is as follows:
可以使用 return command将函数值传回 bash。return 语句终止函数。语法如下
return return [value]
One can force script to exit with the return value specified by [value]. If [value] is omitted, the return status is that of the last command executed within the function or script.
可以强制脚本以 [value] 指定的返回值退出。如果省略 [value]，返回状态将是函数或脚本中最后执行的命令的状态。
Examples
Create a new file called math.sh:
新建一个名为 math.sh 的文件：
#!/bin/bash #!/bin/bash # Name - math.sh # Purpose - Demo return value # ------------------------------------ ## user define function math(){ local a=$1 local b=$2 local sum=$(( a + b)) return $sum } ## call the math function with 5 and 10 as arguments math 5 10 ## display back result (returned value) using $? echo "5 + 10 = $?"
Run it as follows:
运行方法如下
chmod +x math.sh ./math.sh
The above example is straightforward. The return command returns any given value between zero (0) and 255. By default, the value passed by the return statement is the current value of the exit status variable. For example, the following code will return wrong values as it is not between zero (0) and 255.
上面的例子很简单。return 命令 返回介于零 (0) 和 255 之间的任意给定值。默认情况下，return 语句传递的值是 exit status 变量的当前值。例如，以下代码将返回错误的值，因为它不在零（0）和 255 之间。
math 500 100
Here is the proper use of return command (bash-task.sh):
下面是 return command的正确用法（bash-task.sh）：
#!/bin/bash # Name: bash-task.sh # Purpose: Check if a file exists or not using custom bash function and return value # ----------------------------------------------------------------------------------- # set values readonly TRUE=0 readonly FALSE=1 # get input from the CLI file="$1" # return $TRUE (0) if file found # return $FALSE (1) if file not found is_file_found(){ [ -f "$1" ] && return $TRUE || return $FALSE } # show usage info if $1 not passed to our script if [ $# -eq 0 ] then echo "Usage: $0 filename" exit 1 fi # let us call our function is_file_found "$file" # take action based upon return value if [ $? -eq 0 ] then echo "$file added to backup task" else echo "$file not found." fi
Run it as follows:
运行方法如下
chmod +x bash-task.sh ./bash-task.sh ./bash-task.sh /etc/passwd ./bash-task.sh /foo/bar
Passing parameters to a Bash function and return true or false value 向 Bash 函数传递参数并返回 true 或 false 值
How to return custom value from a user-defined function?
As I said earlier, you can't use return command. However, the workaround is as following using the printf command/echo command:
正如前面所说，不能使用 return command。不过，变通方法如下：使用 printf 命令/echo命令：
#!/bin/bash #!/bin/bash # Name - math.sh # Purpose - Demo how to return custom value # ----------------------------------------- ## user define function that use echo/printf math(){ local a=$1 local b=$2 local sum=$(( a + b)) echo $sum } ## call the math function with 5 and 10 as arguments total=$(math 500 42) ## display back result (returned value) using $? echo "500 + 42 = $total"
Listing functions 列出函数
Use the typeset command or declare command.
使用 typeset command或 declare command。
Show the known functions and their code/definitions显示已知函数及其代码/定义
Open the terminal and then run:
打开终端，然后运行：
declare -f declare -f function_name_here ## or ## typeset -f typeset -f function_name_here
How to remove or unset functions 如何删除或取消设置函数
Use the unset command to unset values and attributes of shell variables and functions:
使用 unset 命令 取消设置 shell 变量 和 函数 的值和属性：
unset -f function_name_here unset -f foo unset -f bar
