Shell Scripting

Unix Shell Family tree

Thompson Shell 1971

|_ Bourne (sh) 1977 관리자 기능에서 유용했음

   |_ Korn (ksh) 1983 csh과 ksh의 장점 믹스

|_ Korn (ksh93) 1993 이 때 POSIX Shell이 HPUX의 표준이됨

   |_ Bourne-Again (bash) 1987

|_ Cshell (csh) 1978 자동 완성기능 등 프로그래머들 유용한 커맨드 많음

Which Shell Interprects the Script?  Hash #, bang ! and absolute path

#!/usr/bin/sh    Interpret using the POSIX Shell

#!/bin/sh         Interpret using the POSIX Shell ...

#!/bin/csh        ... C Shell...

Recommended Script Format

First Line - Specify the interpreter

Header - Brief description of the script

Body - Commands to be executed

Last Line - exit# , # is return value

How HP-UX Uses Shell Scripts

1 At system start-up(boot) time

2 At system shutdown

3 As commands

실습

1

$ vi sysinfo.sh

"sysinfo.sh" 1 line, 45 characters

echo "hostname of this machine: $(hostname)"

print "Operating system : $(uname -s)"

print "OS version: $(uname -r)"

$ sysinfo.sh

hostname of this machine: vm161

Operating system : HP-UX

OS version: B.11.31

2

$ cat random.sh

#!/usr/bin/sh

# random.sh

# print some info, then a random number

print "executing random.sh"

print "Today is" $(date)

print "Followin is a random number:  $RANDOM "

exit

$RANDOM 변수는 POSIX Shell 에 의해 결정된다. 확인 방법 $ man sh -> see also -> $ man sh-posix

-> /RANDOM/ 검색

RANDOM         Each time this parameter is evaluated, a random

                     integer, uniformly distributed between 0 and 32767, is  //2^15 = 32768, 15bit

                     generated.  The sequence of random numbers can be

                     initialized by assigning a numeric value to RANDOM.