函数

简介

可以使用函数来组织一组命令变成一个完成特定任务的命令,shell在运行时，会检查函数的语法，但是只有在调用时才会运行，可以在函数内部改变函数外的变量值来达到返回值。

#!/bin/sh

# define function
add_a_user()
{
    # $1、$2...将是定义的函数在使用时传入的参数
    USER=$1
    PASSWORD=$2
    shift; shift;
    COMMENT=$@
    echo "Adding user $USER ($COMMENT) with $PASSWORD"
    useradd -c "$COMMENT" $USER
    passwd $USER $PASSWORD

    a=2
}

# a is script first arg
a=$1
# use the function
add_a_user bob simplepasswd Bob Holness the presenter
add_a_user fred badpassword Fred Durst the singer
add_a_user bilko worsepassword Sgt. Bilko the role modelSgt. Bilko the role model
# a is now 2
echo $a

变量作用域

$ cat test.sh
#!/bin/sh

myfunc()
{
  echo "I was called as : $@"
  x=2
}

echo "Script was called with $@"
x=1
echo "x is $x"
myfunc 1 2 3
echo "x is $x"
$ chmod a+x test.sh
$ ./test.sh a b c
Script was called with a b c
x is 1
I was called as : 1 2 3
x is 2

函数可以在sub-shell中执行，此时需要注意，函数是在另一个进程中运行！例如myfunc 1 2 3 | tee out.log，会打开另一个shell运行此命令，此时原shell中的x将不会被改变，所以x=1。

退出码

return用于返回函数的退出码，此退出码可以在稍后运行函数后，通过$?获得。

#!/bin/sh

adduser()
{
  USER=$1
  PASSWORD=$2
  shift ; shift
  COMMENTS=$@
  useradd -c "${COMMENTS}" $USER
  if [ "$?" -ne "0" ]; then
    echo "Useradd failed"
    return 1
  fi
  passwd $USER $PASSWORD
  if [ "$?" -ne "0" ]; then
    echo "Setting password failed"
    return 2
  fi
  echo "Added user $USER ($COMMENTS) with pass $PASSWORD"
}

## Main script starts here

adduser bob letmein Bob Holness from Blockbusters
ADDUSER_RETURN_CODE=$?
if [ "$ADDUSER_RETURN_CODE" -eq "1" ]; then
  echo "Something went wrong with useradd"
elif [ "$ADDUSER_RETURN_CODE" -eq "2" ]; then 
   echo "Something went wrong with passwd"
else
  echo "Bob Holness added to the system."
fi

编写库

$ cat rename.lib
# common.lib
# 注意由于它是一个库，所以不需要#!/bin/sh来派生一个额外的shell
#
STD_MSG="About to rename some files..."

rename()
{
  # expects to be called as: rename .txt .bak 
  FROM=$1
  TO=$2

  for i in *$FROM
  do
    j=`basename $i $FROM`
    mv $i ${j}$TO
  done
}
$ cat use.sh
#!/bin/sh
# 运行库文件，导入库中的变量和函数
source ./rename.lib
echo $STD_MSG
rename .txt .bak