HPUX - Shell Advanced Features

Shell Variable Storage : Local Variables + Environment Variables + Program Code (/usr/bin/sh)

{

$ name=yohan

$ set

...

name=yohan

....

}

Variable Substitution

$var : Directs the shell to perform variable substitution

{

$ echo $PATH

/usr/bin:/usr/contrib/bin: ...

$ PATH=$PATH:$HOME

/usr/bin: .... :/home/user11

}

Command Substitution

$(command) 

Process and Variable (Parent Child)

1 fork : program and data spaces are duplicated

2 exec : program and local data space are replaced with program and data of requested program (/usr/bin/vi) and program is executed 

{

$ ps -f

     UID   PID  PPID  C    STIME TTY       TIME COMMAND

    root 16761  1222  0 14:55:51 pts/te    0:00 telnetd -b /etc/issue

  user11 17268 16762  1 15:47:58 pts/te    0:00 ps -f

  user11 16762 16761  0 14:55:51 pts/te    0:00 -sh

UserID ProcessID Process'ParentID CPU StartTime 

telnetd -> sh -> ph-f 

Parent     Child  Child

...

}

{

$ ps -f

     UID   PID  PPID  C    STIME TTY       TIME COMMAND

  user11 17472 16762  0 15:55:54 pts/te    0:00 ps -f

    root 16761  1222  0 14:55:51 pts/te    0:00 telnetd -b /etc/issue

  user11 16762 16761  0 14:55:51 pts/te    0:00 -sh

$ color=red

$ echo $color

red

$ ksh

$ echo $color

} // child process에서는 parent의 local variable을 읽을수 없다.

{

$ exit

$ export color    //env. var로 변경

$ env

$ ksh

$ echo $color

red

$ color=blue

$ env

...

color=blue

...

$ exit 

$ echo $color

} // environment variable로 변경 후 읽을수 있음, child process의 environment variable 변경은 parent process에 상속되지 않는다. 

{

$ MYNAME='YO HAN'

$ echo $MYNAME

YO HAN

$ sh

$ echo $MYNAME

YO HAN

$ exit

$ vi .shrc

add line 

}