?V?F???X?N???v?g?ő??㩁Awhile????F?X?}?[?g?Ȑa?m?̂??߂̃V?F???X?N???v?g?i8?j?i1/2 ?y?[?W?j

?V?F???X?N???v?g?ő??㩁Fwhile???

?@?O???̓V?F???X?N???v?g?v???O???~???O?̃R?c??1?‚Ƃ??āu?A?b?g?E?A?E?O?????X???v???Љ???B?Љ?̒???while???????N?????₷?????ɂ‚??ĐG?ꂽ???A?O??̐????????ł͂悭??????Ȃ?????????????Ǝv???B

?@????͂??́uwhile????v?ɏœ_?𓖂āA?V?F???X?N???v?g?v???O???~???O?ōł??͂܂?₷???????@?艺???Đ???????B

while?ƃp?C?v?̑g?ݍ??킹?Ŗ?蔭??

?@???̃V?F???X?N???v?g?????Ăق????B???s???ʂ?\?????Ăق????̂????A?????炭?قƂ?ǂ̕????u?W???o?͂?Linux???o?͂????v?Ɠ????邾?낤?B

#!/bin/sh
OS=FreeBSD
while :
do
        OS=Linux
        break
done
echo ${OS}

?@???x?͎??̃V?F???X?N???v?g?̎??s???ʂ?z?????Ă݂Ăق????B?????Łu?W???o?͂?Linux???o?͂????v?ƍl???????́A????̘b?͍Ō?܂œǂ񂾂ق????ǂ??Ƃ??????ƂɂȂ?B????u?W???o?͂?FreeBSD???o?͂????v?Ɠ????A???A???̗??R???V?X?e???R?[???̓????????グ?Đ????ł?????́A????̘b?͂????Ő؂?グ?Ă?????Ă??\??Ȃ??B

#!/bin/sh
OS=FreeBSD
echo |
while :
do
        OS=Linux
        break
done
echo ${OS}

?@???s????Ǝ??̂悤?ɂȂ?B

$ ./while01.sh 
Linux
$ ./while02.sh
FreeBSD
$

?@???????Ⴄ?̂́A?u?V?F???̓p?C?v???g?p?????ƁA?R?}???h?̕??????V?F????fork(2)???Afork(2)???Đ??????ꂽ?V?F???̕??ŃR?}???h?????s????v???߂??B?ȍ~?ŃV?F???̓????ʼn??????s????Ă???̂??ǂ??Ă??????B

?p?C?v?̓R?}???h?̕??????V?F????fork(2)??K?v?Ƃ???

?@truss(1)???g???ăV?X?e???R?[???̓?????ǂ??B?f?[?^?̉??H?ɕ֗??Ȃ̂ŁA?R?}???h?Ƃ???Open usp Tukubai???g?p????B?ǎ???????ꍇ?ɂ͂??̃R?}???h???g???Ă݂Ăق????B????A?ŏ?????Open usp Tukubai???Z?b?g?A?b?v???ꂽVirtualBox???z?‹??̃C???[?W?t?@?C???̔z?z???n?܂????̂ŁA?????Ă݂?ɂ͂???????_?E?????[?h?????????ȒP????????Ȃ? ?iTukubai on FreeBSD 9.1-RC1?j?B

$ truss -c ./while01.sh 2>&1 | tail +3 | ctail -2 |
self 1 3 | sort -k1,1 | keta
     access  3
      close 11
      fcntl  2
      fstat 10
    getegid  1
    geteuid  2
     getgid  1
     getpid  1
    getppid  1
     getuid  1
      lseek  3
      lstat  2
       mmap 20
     munmap  7
       open 11
       read 12
   readlink  1
  sigaction  8
sigprocmask 10
       stat  2
      write  1
$ 

$ truss -c ./while02.sh 2>&1 | tail +3 | ctail -2 |
self 1 3 | sort -k1,1 | keta
     access  3
      close 13
      fcntl  2
       fork  2
      fstat 10
    getegid  1
    geteuid  2
     getgid  1
    getpgrp  1
     getpid  1
    getppid  1
     getuid  1
      lseek  3
      lstat  2
       mmap 20
     munmap  7
       open 11
       pipe  1
       read 12
   readlink  1
  sigaction  8
sigprocmask 10
       stat  2
      write  1
$

?@ctail(1)??self(1)?Aketa(1)??Open usp Tukubai?̃R?}???h???B?e?L?X?g?̐??`?ɕ֗??Ȃ̂ł悭???p????B?g???????I?????C???}?j???A???ɂ܂Ƃ܂??Ă???B

?@?g???Ă???V?X?e???R?[???̍??ق????????o???Ǝ??̂悤?ɂȂ?B?p?C?v?????񂾕???fork(2)?V?X?e???R?[????2??Apipe(2)?V?X?e???R?[????1??A?V?????lj?????Ă??邱?Ƃ???????B

--- truss01     2012-09-09 17:06:28.846231611 +0900
+++ truss02     2012-09-09 17:08:11.563231300 +0900
@@ -1,12 +1,14 @@
-$ truss -c ./while01.sh 2>&1 | tail +3 | ctail -2 |
+$ truss -c ./while02.sh 2>&1 | tail +3 | ctail -2 |
 self 1 3 | sort -k1,1 | keta
      access  3
-      close 11
+      close 13
       fcntl  2
+       fork  2
       fstat 10
     getegid  1
     geteuid  2
      getgid  1
+    getpgrp  1
      getpid  1
     getppid  1
      getuid  1
@@ -15,6 +17,7 @@
        mmap 20
      munmap  7
        open 11
+       pipe  1
        read 12
    readlink  1
   sigaction  8

?@?p?C?v??????ł???̂?????Apipe(2)?V?X?e???R?[?????lj?????Ă???͓̂??R???B????fork(2)???Ȃ?2??Ă΂?Ă???̂??A?Ƃ????_?ɂ???B

?@?????ŁA???̂悤?ȃV???v???ȃ??f?????l???Ă݂悤?B

a | b

?@?V?F???͂??̂悤?ȃ??C?????p?[?X????ƁA?܂????????g??2??fork(2)????B?????āAfork(2)???Đ????????q?v???Z?X?̓??o?͂?pipe(2)?Őڑ?????B

??????fork(2)???Ă???a?????s <==???̊Ԃ?pipe(2)?Őڑ?==> ??????fork(2)???Ă???b?????s

?@?R?}???h?̓??o?͂?pipe(2)?Őڑ????邽?߂ɂ́A???ꂼ????•ʂ̃v???Z?X?Ƃ??ēƗ??????Ȃ???΂Ȃ?Ȃ??B???̂???fork(2)???Ďq?v???Z?X?𐶐????Ă???B?p?C?v??4?Žg???Ă???΁A5??fork(2)?????s???Ďq?v???Z?X?𐶐????A??????pipe(2)?Őڑ?????B?Ⴆ?΃p?C?v??4?˜A?????Ďg???Ă???΁Afork(2)??5????s?????B

?@???̎q?v???Z?X?́A?V?F???ł͂?????u?T?u?V?F???v?ƌĂ΂??B