Function of Shell programming

functions: Function functions are statement blocks consisting of several shell commands for code reuse and modular programming


1) Definition of function:Can be defined in the command line, part of the script, only in a separate file of the function
Two parts: function name and function body; functions can have return status value returned #
-Syntax One:
function F_name {
... function Body ...
}

-Syntax Two:
F_name () {
... function Body ...
}
Define and invoke functions at the command line

] #dir () {ls;}] #dir

2) Call to function:function is only executed if it is called
Given function name:
No parameter call F_name
There are parameters called F_name arg1 arg2 ...

When the function is called, it is created and terminates on return.

Command line: After defining a function, you can call directly using the #unset f_name undo function

In script: function is defined before it can be used, the function should be placed at the beginning of the script

Function file: Writes a common function to a function file, and loads the function file in the command line or script to invoke the function
#set View all loaded functions #unset delete functions

Load function:
Source/path/to/filename
. /path/to/filename

Load function File

] #vi Echo.sh#!/bin/bash#zjjprint_haha () {echo haha}] #source echo.sh] #print_haha] #haha

3) Function parameters
Pass parameters to the function:
F_name arg1 arg2.

The function body can use $1,$2,... Call the corresponding parameter; [Email protected],$*,$ #等同样可用

    4) function variables      Note that the operation of the variables in the function body affects the entire script,
         can define local variables in the function. Valid only for function body, use LOCAL
        local var_name= VALUE
  
    5) Recursive
         function directly or indirectly calls itself
         note the number of recursive layers
 

===  Function Exercises:
 
 1. Write a service script/root/bin/testsrv.sh

#!/bin/bash#zjjtestsrv ()  {    bsname= ' basename $0 '     local  srvpath=/var/lock/subsys/$bsname         case $1 in     start)                  if [ -e  $Srvpath  ] ;then                         echo  +   $bsname  is running                 else                         touch  $Srvpath  & & echo ++ start successful                   fi                 ;;         stop)                  if [ -e  $Srvpath  ] ;then                          rm -f  $Srvpath  &&echo -- stop successful                 else                          echo -   $bsname  is dead                 fi                 ;;         restart)                  testsrv stop && testsrv start                 ;;         status)                  [ -e  $Srvpath  ] &&echo +    $bsname  is running...  | | echo -   $bsname  is stopped...                 ;;         *)                  testsrv status                 ;;         esac                 }testsrv $1

2. Write a script/root/bin/copycmd.sh, copy the command and its library file

#!/bin/bash#zjjcopycmd ()  {# create directiry if they does not exist     local dpath= '/testdir/sysroot '     for dir in  ' echo  $PATH |tr  ': '   '   '   '/lib '   '/lib64 '  ;d o    [ -e  ${dpath}${dir} ] &&continue | | mkdir -p ${dpath}${dir}    done    while true ;d o     read -p  "++enter a command or [quit]:"  cmd     [[  $cmd  =~ quit ]] &&exit 23     Spath= ' whereis -b  $cmd  2>/dev/null|cut -d  '   '  -f2 '      ! [ $? -eq 0 ] && echo invalid command & &continue    cp -a  $spath  ${dpath} $spath &&echo copy   $spath  ++succesful | | echo --error        for so in  ' ldd  $spath  |sed -nr  ' s/.*>  ([^[:space:]].*)  \ (. */\1/p ";d o         cp -n  $so  ${dpath} $so  &&echo -e  "copy   $so    \t++successful " | | Echo --error    donedone}copycmd

3. write a function to implement two numbers as parameters, return the maximum value

#!/bin/bash#zjjmax () {[$1-gt $]&&echo max:$1| | Echo Max:$2}max $ A

4. Fibonacci Sequence

#!/bin/bash#zjjfibo ()  {    if [ $1  -le 1 ];then        echo $1         elif [ $1 -gt 1 ];then         echo  "$[$ (Fibo $[$1-1]) +$ (Fibo $[$1-2])]"     fi}if !  [ $1 -eq $1 ]&>/dev/null| | [ $1 -lt 0 ]&>/dev/null| | [ -z $1 ] ;then    echo please enter a integer  &&exit 23else    for ((i=0;i<=$1;i++));d o         fibo  $i     donefi 

5. Hanoi Tower Solution

#!/bin/bash#zjj# move n-1: A to b# move n:a to C # move n-1: B to Chanoi () {if [$1-eq 1];then echo $ t o $4 else Hanoi $[$1-1] $ $4 $ echo $ to $4 Hanoi $[$1-1] $ $ $4 fi}hanoi $ A B C

This article is from the "mediocre" blog, please be sure to keep this source http://zzjasper.blog.51cto.com/9781564/1840791

Function of Shell programming