Shell basic function writing

One, why do you need to use functions

 Because the shell does not have the concept of modules and classes, when we have a large number of scripts that need to be executed in order to implement a function, for the convenience of operation, these codes will be put together and executed by calling a specific name..Improve the reuse rate of scripts and optimize the code structure.

Second, grammar

 [function] method name(){Script to be executedUsually, [function is omitted or not written]}

Three, pass parameters

 3.1shell only supports 9 parameters by default. $1 and $2 represent the first parameter respectively. You can use shift to pass more parameters.

 3.2, $# represents the number of incoming parameters, excluding $03.3, $$ indicates the pid of the current script execution3.4, $! The last running pid in the backgroundAdditional understanding:The difference between $a and $*:When passing parameters between functions, "$a" will not break up the passed parameters; $* will break up the passed parameters

Four, function call

 4.1. Function call: When calling a function, you can directly call it by entering the function name4.2, parameter passing: add a space after the function name, and then keep up with the parameters that need to be passed

Five, debug

 1. Provide parameters at the beginning of the script #! /bin/sh -x2.-v means print to standard error output during execution3.-n will read the script once, but will not execute the script, it will check for syntax errors-------------------- Self-discipline is not easy, I hope you can stick to it