Function of shell script 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

-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:-F    3,7 else echo "No such user." Fi}username=$1userinfousername=$2userinfo

Example 2: Service scripting framework

#!/bin/bash## chkconfig: - 50 50# description: test service script# prog=$ (basename $0) lockfile=/var/lock/subsys/$progstart ()  {    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&nbSP; " $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 $1 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 existsaddusers ()  {    if id $1  &> /dev/null; then        return 5     else        useradd $1         retval=$?        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."     fidone

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=tomsetname () {local name=jerry echo "Function: $name"}setnameecho "Shell: $name"

function recursion:

The function calls itself directly or indirectly;

Example: Implement the following functions

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]) F I}fact $

The following sequence is implemented:

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 $idoneecho

This article is from the "Wang Liming" blog, make sure to keep this source http://afterdawn.blog.51cto.com/7503144/1916045

Function of shell script programming