Function of Shell programming

Functions: function

Program Programming: Code Reuse

Modular programming

Structured programming

The code of an independent function as a whole, and a name for it; a named code snippet, which is a function;

Note: The code snippet that defines the function is not executed automatically and is executed at call time;

Any location where the function name appears, is automatically replaced with the function code when the code executes;

Syntax One:

function F_name {

... function Body ...

}

Syntax Two:

F_name () {

... function Body ...

}

The life cycle of a function: created every time it is called, terminates when returned;

Its status returns the result of the state of the last command running in the function body;

To customize the status return value, you need to use: return

return [0-255]

0: Success

1-255: Failure

Example: Given a user name, get the ID number of the user and the default shell;

#!/bin/bash

#

UserInfo () {

If ID "$username" &>/dev/null; Then

grep "^ $username \>"/etc/passwd | Cut-d:-f3,7

Else

echo "No such user."

Fi

}

Username=$1

UserInfo

Username=$2

UserInfo

Example 2: Service scripting framework

#!/bin/bash

#

# Chkconfig:-50 50

# description:test Service Script

#

prog=$ (basename)

lockfile=/var/lock/subsys/$prog

Start () {

If [-f $lockfile]; Then

echo "$prog is running yet."

Else

Touch $lockfile

[$?-eq 0] && echo "Start $prog finshed."

Fi

}

Stop () {

If [-f $lockfile]; Then

Rm-f $lockfile

[$?-eq 0] && echo "Stop $prog finished."

Else

echo "$prog is not running."

Fi

}

Status () {

If [-f $lockfile]; Then

echo "$prog is running"

Else

echo "$prog is stopped."

Fi

}

Usage () {

echo "Usage: $prog {start|stop|restart|status}"

}

Case $ in

Start

start;;

Stop

stop;;

Restart

Stop

start;;

Status

status;;

*)

Usage

Exit 1;;

Esac

function return value:

The return value of the function's execution result:

(1) using the Echo or printf command to output;

(2) The execution result of the command called in the function body;

Exit status code for the function:

(1) The default depends on the exit status code of the last command executed in the function body;

(2) Custom: Return

The function can accept parameters:

Pass parameters to the function:

In the function body, you can use $1,$2, ... A reference to a parameter passed to a function; You can also use $* or [email protected] in a function to reference all parameters, $ #引用传递的参数的个数;

When calling a function, the given argument list is separated by a whitespace character after the function name, for example, TestFunc arg1 arg2 arg3 ...

Example: Add 10 users,

Add the user's function using function implementation, user name as parameters passed to the function;

#!/bin/bash

#

# 5:user exists

AddUsers () {

If ID $ &>/dev/null; Then

Return 5

Else

Useradd $

Retval=$?

Return $retval

Fi

}

For i in {1..10}; Do

AddUsers ${1}${i}

Retval=$?

If [$retval-eq 0]; Then

echo "ADD user ${1}${i} finished."

elif [$retval-eq 5]; Then

echo "User ${1}${i} exists."

Else

echo "Unkown Error."

Fi

Done

Exercise: Write a script;

Use the function to ping a host to test the host's online status, and the host address is passed to the function via parameters;

Main program: Test the online status of each host in the 172.16.1.1-172.16.67.1 range;

Exercise: Write a script;

Print the nn multiplication table;

Variable scope:

Local variables: The scope is the life cycle of the function, and is automatically destroyed at the end of the function;

Methods for defining local variables: local variable=value

Local variable: The scope is the life cycle of the shell process that runs the script, so its scope is the current shell script file;

Sample program:

#!/bin/bash

#

Name=tom

SetName () {

Local Name=jerry

echo "Function: $name"

}

SetName

echo "Shell: $name"

function recursion:

The function calls itself directly or indirectly;

10!=10*9!=10*9*8!=10*9*8*7!= ...

N

N (n-1)!=n* (n-1) * (n-2)! =

#!/bin/bash

#

Fact () {

If [$1-eq 0-o $1-eq 1]; Then

Echo 1

Else

echo $[$1*$ (fact $[$1-1])

Fi

}

Fact $

1,1,2,3,5,8,13,21,...

#!/bin/bash

#

Fab () {

If [$1-eq 1]; Then

Echo-n "1"

elif [$1-eq 2]; Then

Echo-n "1"

Else

Echo-n "$[$ (Fab $[$1-1]) +$ (Fab $[$1-2])]"

Fi

}

For I in $ (seq 1 $); Do

Fab $i

Done

Echo

Function of Shell programming