Function programming loop statements and functions

Programming loop statements and functions

Function application example

Example 1

• Sum two numbers
  1). Define the function through sum(){}
  2). Use the read command to interactively input two numbers and sum them.
  Example 2
• Write user-defined functions that can be used after logging in to the system
  1). Edit the user-defined function file /root/functiong
  2). Load the executable function file /root/function in the current shell
  3). In ~/.bashrc Add the soure /root/function command to the file

Function scope

• Functions in Shell scripts are only valid in the current Shell environment
• The variable in Shell script is global by default
• Use the local command to limit the variable to the function
• Example
  1. The internal variables of the function are realized by local
  1). By defining the myfun function, the local variable i is set inside it
  2). The internal and external values ​​of the function are assigned respectively, and the result is verified

Function parameters

• Usage of parameters
  Function name Parameter 1 Parameter 2 Parameter 3

• Representation of parameters
  $1 $2 $3 $4

• Example
  1. Write log information into a file through function parameters
  1). Realize by defining appendfile function

recursive function

• Call its own function
• Example
  1. Recursively traverse directories
  1) Realize by defining the recursive function list_files

Shell function

• Write the sequence of commands together in a format

• Easy to reuse command sequence

• Shell function definition
  [function] function name () { command sequence [return x] }
  
  
  

• How to call the function
  Function name [Parameter 1] [Parameter 2]

Shell array

• Application scenarios include
  1. Get array length
  2. Get element length
  3. Traverse elements
  4. Element slice
  5. Element replacement
  6. Element deletion