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<shui @ cs.tsukuba.ac.jp>

$B$3$N%Z!<%8$O!$ http://www.coins.tsukuba.ac.jp/~syspro/2005/No3.html
$B%7%9%F%`%W%m%0%i%`$N%[!<%`%Z!<%8!J(B2005$BG/EY!K(B
http://www.coins.tsukuba.ac.jp/~syspro/2005/
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     1  #include <stdio.h>
     2
     3  extern char **environ;
     4
     5  int     data0;
     6  int     data1 = 10;
     7
     8  main(int argc, char *argv[])
     9  {
    10          char c;
    11
    12          printf("environ:\t%0.8p\n", environ);
    13          printf("argv:\t\t%0.8p\n", argv);
    14          printf("stack:\t\t%0.8p\n", &c);
    15
    16          printf("bss:\t\t%0.8p\n", &data0);
    17          printf("data:\t\t%0.8p\n", &data1);
    18  }

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% ./a.out 
environ:        0xbfffdc5c
argv:           0xbfffdc54
stack:          0xbfffdbe7
bss:            0x080496e8
data:           0x080495f0
%

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char *getenv(const char *name);
int   putenv(char *string);
int   setenv(const char *name, const char *value, int overwrite);
void  unsetenv(const char *name);

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kill	$B%W%m%;%9$N!J6/@)!K=*N;(B
nice	$B%W%m%;%9$N
limit	$B%W%m%;%9$NMxMQ2DG=;q8;$N@)8f(B
gdb, strace	$B%G%P%C%0%D!<%k(B

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pid_t fork(void);
int   execve  (const char *filename, char *const argv[], char *const envp[]);
pid_t wait(int *status)
void  exit(int status);

fork $B%7%9%F%`%3!<%k$O!$(Bfork $B%7%9%F%`%3!<%k$r8F$s$@%W%m%;%9$NJ#@=$r:n@.$9$k!%(B fork $B%7%9%F%`%3!<%k$r8F$s$@%W%m%;%9$,?F%W%m%;%9$H$J$j!$J#@=$5$l?7$?$K:n$i$l$?%W%m%;%9$,;R%W%m%;%9$K$J$k!%(B execve $B%7%9%F%`%3!<%k$O!$(Bexecve $B%7%9%F%`%3!<%k$r8F$s$@%W%m%;%9$K;XDj$5$l$?%W%m%0%i%`$r%m!<%I!$

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fork$B$O<+J,$r%3%T!<$7$F;R%W%m%;%9$r:n$k!%(B $B8=:_l=j$b%3%T!<$9$k!%(B $B=>$C$F!$(B$B;R%W%m%;%9$O(B fork $B$+$iLa$k$H$3$m$+$i%W%m%;%9$N$B!%(B fork $B$r8F$S=P$7$??F%W%m%;%9$b(B fork $B$+$iLa$k!JF1$8$/(B19$B9TL\!K!%(B $B$I$A$i$,?F$G$I$A$i$,;R$+$O!$(Bfork $B$NLa$jCM$+$iH=JL$9$k$3$H$,$G$-$k!J(B24$B9TL\!K!%(B fork $B$O?F%W%m%;%9$K$O@8@.$7$?;R%W%m%;%9$N%W%m%;%9(BID$B$rLa$jCM$H$7$FJV$9!%(B $B;R%W%m%;%9$K$O(B 0 $B$rJV$9!%(B fork $B$,<:GT$7$?;~$K$OIi$NCM$rJV$9!%(B

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     1  #include <stdio.h>
     2  #include <sys/types.h>
     3  #include <sys/wait.h>
     4
     5  extern char **environ;
     6
     7  void
     8  do_child()
     9  {
    10          printf("This is child(pid=%d).\n", getpid());
    11
    12          exit(2);
    13  }
    14
    15  main()
    16  {
    17          int child, status;
    18
    19          if ((child = fork()) < 0) {
    20                  perror("fork");
    21                  exit(1);
    22          }
    23
    24          if (child == 0)
    25                  do_child();
    26          else {
    27                  if (wait(&status) < 0) {
    28                          perror("wait");
    29                          exit(1);
    30                  }
    31                  printf("The child (pid=%d) existed with status(%d).\n",
    32                      child, WEXITSTATUS(status));
    33          }
    34  }

$B0J2<$O!$$3$N%W%m%0%i%`$r%3%s%Q%$%k!$

% ./a.out 
This is child(pid=23656).
The child (pid=23656) existed with status(2).
%

$B%W%m%0%i%`Nc!J(Bexecve$B!K(B

$B0J2<$O(B execve $B$r;HMQ$7$?4JC1$J%W%m%0%i%`Nc$G$"$k!%(B $B$3$N%W%m%0%i%`$O(B /bin/ls $B$r0z?t$J$7$Ge=q$-$5$l$k$h$&$K%m!<%I$5$l(B /bin/ls $B%W%m%0%i%`$N(B main $B4X?t$+$i

execve $B$K$O!$0z?t!$4D6-JQ?t$O$=$l$>$l%W%m%;%9$,I,MW$H$9$k7A<0!J(Bargv$B7A<0!K$GEO$9I,MW$,$"$k!%(B argv $B$O!$(Bchar* $B7?$NG[Ns$r@k8@$7!J(B7$B9TL\!K!$MWAG$KCM$r%;%C%H$7$F$$$k!J(B9, 10$B9TL\!K!%(B $B4D6-JQ?t$O!$8=:_$N4D6-JQ?t$NCM$r$=$N$^$^EO$7$F$$$k!%(B

execve $B$O!$%7%'%k$N$h$&$K$C$F!$

     1  #include <stdio.h>
     2
     3  extern char **environ;
     4
     5  main()
     6  {
     7          char *argv[2];
     8
     9          argv[0] = "/bin/ls";
    10          argv[1] = NULL;
    11
    12          execve(argv[0], argv, environ);
    13  }

$B$C$F!$0J2<$N$h$&$K=q$$$F$b!$(B/bin/ls $B$O

     1  #include <stdio.h>
     2
     3  extern char **environ;
     4
     5  main()
     6  {
     7          char *argv[2];
     8
     9          argv[0] = "ls";
    10          argv[1] = NULL;
    11
    12          execve("/bin/ls", argv, environ);
    13  }

execve $B$Gl9g$O!$(Bargv[1] $B0J9_$K;XDj$9$l$PNI$$!%(B $B0J2<$O(B /bin/ls / $B$r

     1  #include <stdio.h>
     2
     3  extern char **environ;
     4
     5  main()
     6  {
     7          char *argv[3];
     8
     9          argv[0] = "/bin/ls";
    10          argv[1] = "/";
    11          argv[2] = NULL;
    12
    13          execve(argv[0], argv, environ);
    14  }

% ./a.out 
bin   dev  home    lhome  lost+found  mnt  proc  sbin  usr  work
boot  etc  initrd  lib    misc        opt  root  tmp   var
%

$B%W%m%0%i%`Nc!J(Bfork&execve$B!K(B

$B>e5-$N(B fork $B$N%W%m%0%i%`$H(B execve $B$N%W%m%0%i%`$rAH$_9g$o$;$k$H!$0J2<$N$h$&$K$J$k!%(B

     1  #include <stdio.h>
     2  #include <sys/types.h>
     3  #include <sys/wait.h>
     4
     5  extern char **environ;
     6
     7  void
     8  do_child()
     9  {
    10          char *argv[3];
    11
    12          printf("This is child(pid=%d)\n", getpid());
    13
    14          argv[0] = "/bin/ls";
    15          argv[1] = "/";
    16          argv[2] = NULL;
    17
    18          execve(argv[0], argv, environ);
    19  }
    20
    21  main()
    22  {
    23          int child, status;
    24
    25          if ((child = fork()) < 0) {
    26                  perror("fork");
    27                  exit(1);
    28          }
    29
    30          if (child == 0)
    31                  do_child();
    32          else {
    33                  if (wait(&status) < 0) {
    34                          perror("wait");
    35                          exit(1);
    36                  }
    37                  printf("The child (pid=%d) existed with status(%d).\n",
    38                      child, WEXITSTATUS(status));
    39          }
    40  }

% ./a.out 
This is child(pid=23774)
bin   dev  home    lhome  lost+found  mnt  proc  sbin  usr  work
boot  etc  initrd  lib    misc        opt  root  tmp   var
The child (pid=23774) existed with status(0).
%

$Bl9g!$(Bexecve $B$,<:GT$9$k2DG=@-$b9M$($J$1$l$P$J$i$J$$!%(B execve $B$O%W%m%0%i%`$N

     1  #include <stdio.h>
     2  #include <sys/types.h>
     3  #include <sys/wait.h>
     4
     5  extern char **environ;
     6
     7  void
     8  do_child()
     9  {
    10          char *argv[2];
    11
    12          printf("This is child(pid=%d)\n", getpid());
    13
    14          argv[0] = "/bin/xxxxx";
    15          argv[1] = NULL;
    16
    17          if (execve(argv[0], argv, environ) < 0) {
    18                  perror("execve");
    19                  exit(1);
    20          }
    21  }
    22
    23  main()
    24  {
    25          int child, status;
    26
    27          if ((child = fork()) < 0) {
    28                  perror("fork");
    29                  exit(1);
    30          }
    31
    32          if (child == 0)
    33                  do_child();
    34          else {
    35                  if (wait(&status) < 0) {
    36                          perror("wait");
    37                          exit(1);
    38                  }
    39                  printf("The child (pid=%d) existed with status(%d).\n",
    40                      child, WEXITSTATUS(status));
    41          }
    42  }

$B>e5-$N%W%m%0%i%`$r

% ./a.out 
This is child(pid=23797)
execve: No such file or directory
The child (pid=23797) existed with status(1).
%

$B$=$NB>$N%7%9%F%`%3!<%k(B

exit $B$O8=:_$O%i%$%V%i%j4X?t$H$J$C$F$*$j!$(B_exit $B$,%7%9%F%`%3!<%k$G$"$k!%(B $BFCDj$N%W%m%;%9$N=*N;$rBT$D$K$O(B waitpid $B$r;HMQ$9$k!%(B

void  _exit(int status);
pid_t waitpid(pid_t pid, int *status, int options);

$B$J$<(B exit $B$O%i%$%V%i%j4X?t$K$J$C$F$$$k$N$+$O!$(Batexit(3)$B$d(Bon_exit(3)$B$r8+$F$_$k$H$o$+$k!%(B

$B%W%m%0%i%`

execve $B$O0z?t$d4D6-JQ?t$r(B argv $B7A<0$GEO$9I,MW$,$"$k!$$^$?%W%m%0%i%`$N%5!<%A$7$F$/$l$J$$$?$a!$$b$&>/$74JC1$K;H$($k$h$&$K$H!$0J2<$N%i%$%V%i%j4X?t$,MQ0U$5$l$F$$$k!%(B

int  execl(const char *path, const char *arg, ...);
int  execlp(const char *file, const char *arg, ...);
int  execle(const char *path, const char *arg , ..., char * const envp[]);
int  execv(const char *path, char *const argv[]);
int  execvp(const char *file, char *const argv[]);

execl, execlp, execle $B$O!$%3%^%s%I0z?t$NEO$7J}$,(B execve $B$H$O0[$J$j!$$3$l$i$N%i%$%V%i%j4X?t$N0z?t$H$7$F!$%3%^%s%I0z?t$N$N$h$&$KJ8;zNs$rJB$Y$FEO$9!%(B

     1  #include <stdio.h>
     2
     3  void
     4  main()
     5  {
     6          execl("/bin/ls", "ls", "/", NULL);
     7  }

$B$^$?!$(Bexeclp, execvp $B$O4D6-JQ?t(B PATH $B$r;HMQ$7$F%3%^%s%I$r%5!<%A$7$F$/$l$k!%(B

     1  #include <stdio.h>
     2
     3  void
     4  main()
     5  {
     6          execlp("ls", "ls", "/", NULL);
     7  }

$B%j%@%$%l%/%7%g%s!$%Q%$%W(B

$B%j%@%$%l%/%7%g%s(B

$B35MW(B

$B%j%@%$%l%/%7%g%s$OI8=`F~=PNO$r%U%!%$%k$K$9$k5!G=$G$"$k!%(B $B0J2<$O!$%7%'%k$+$i(B ls $B$N7k2L$r%U%!%$%k$K=PNO$7$?$j!$(Bwc $B$X$NF~NO$r%U%!%$%k$K$7$?$j$7$F$$$k!%(B

% ls *.c > a.txt 
% wc < a.txt 
     38      38     374
%

$B%j%@%$%l%/%7%g%s$K$h$jF~=PNO$r%U%!%$%k$KBP$7$F9T$&$H$$$&=hM}$O(B ls, wc $B$H$OL54X78$K9T$o$l$F$$$k!%(B $B%W%m%;%9$NI8=`F~=PNO$O!$%U%!%$%k%G%#%9%/%j%W%?$N(B 0, 1, 2 $B$K3d$jEv$F$i$l$F$$$k!%(B $B$3$l$i$N%U%!%$%k%G%#%9%/%j%W%?$N@h$,2?$G$"$k$+$O!$%W%m%;%9$O4XCN$7$J$$!%(B $B%W%m%;%9$O(B 0 $B$OI8=`F~NO!$(B1 $B$OI8=`=PNO!$(B2 $B$OI8=`%(%i!<=PNO$G$"$k$H$7$F=hM}$r9T$&!%(B

execve $B$O%W%m%0%i%`$re=q$-$7$=$N%W%m%0%i%`$N(B main $B4X?t$+$i$NB0@-$OJQ99$7$J$$!%(B $B$=$3$G%U%!%$%k%G%#%9%/%j%W%?(B 0 $B$N@h$r%U%!%$%k$K$7$F$7$^$C$F$+$i(B execve $B$r8F$V$H!$(Bexecve $B$K$h$C$F5/F0$5$l$k%W%m%0%i%`$,I8=`F~NO$O$=$N%U%!%$%k$K$J$C$F$7$^$&!%(B $B=>$C$F!$I8=`F~NO$+$i$NFI$_9~$_$r9T$&$H!$$=$N%U%!%$%k$NFbMF$,FI$_9~$^$l$k$3$H$K$J$k!%(B $B$^$?!$%U%!%$%k%G%#%9%/%j%W%?(B 1 $B$N@h$r%U%!%$%k$K$7$F$7$^$C$F$+$i(B execve $B$r8F$V$H!$(Bexecve $B$K$h$C$F5/F0$5$l$k%W%m%0%i%`$,I8=`=PNO$X$N=q$-9~$_$O!$$=$N%U%!%$%k$X$N=q$-9~$_$H$J$k!%(B

$B%U%!%$%k$NF~=PNO$N$?$a$N%U%!%$%k%G%#%9%/%j%W%?$NCM$H$7$F(B 0, 1, 2 $B$r;HMQ$9$k$K$O!$%U%!%$%k%G%#%9%/%j%W%?$NIU$1BX$($r$7$F$/$l$k%7%9%F%`%3!<%k(B dup, dup2 $B$r8F$V!%(B $B$I$A$i$b;XDj$5$l$?%U%!%$%k%G%#%9%/%j%W%?$NJ#@=$r:n@.$9$k!%(B $B8F=P$78e$O!$8E$$%U%!%$%k%G%#%9%/%j%W%?$b(B dup, dup2 $B$K$h$C$F:n@.$5$l$??7$7$$%U%!%$%k%G%#%9%/%j%W%?$b!$F1$8$b$N$H$7$F;HMQ$G$-$k>uBV$K$J$C$F$$$k!%(B $B8E$$%U%!%$%k%G%#%9%/%j%W%?$,ITMW$G$"$l$P(B close $B$7$J$1$l$P!$8E$$%U%!%$%k%G%#%9%/%j%W%?$OM-8z$J>uBV$K$J$C$F$$$k!%(B $B8E$$%U%!%$%k%G%#%9%/%j%W%?$r(B close $B$7$F$b!$?7$7$$%U%!%$%k%G%#%9%/%j%W%?$OM-8z$J$^$^$G$"$k!%(B

int dup(int oldfd);
int dup2(int oldfd, int newfd);

dup $B$O%U%!%$%k%G%#%9%/%j%W%?$H$7$F;HMQ$5$l$F$$$J$$:G>.$NCM$r;HMQ$7!$(Bdup2 $B$O(B newfd $B$H$7$F;XDj$5$l$?CM$r;HMQ$9$k$H$$$&E@$@$1$,0[$J$k!%(B

dup2 $B$r;HMQ$7$?%j%@%$%l%/%7%g%s$N@_Dj$r?^<($9$k$H!$0J2<$N$h$&$K$J$k!%(B

$B%U%!%$%k$r%*!<%W%s$7!$!JNc$($P!K%U%!%$%k%G%#%9%/%j%W%?(B 3 $B$rF@$k!%(B
$BI8=`F~NO!J%U%!%$%k%G%#%9%/%j%W%?(B 0$B!K$r%/%m!<%:$9$k!%(B
dup2 $B$K$h$j!$%U%!%$%k%G%#%9%/%j%W%?(B 3 $B$NJ#@=$r%U%!%$%k%G%#%9%/%j%W%?(B 0 $B$H$7$F:n@.$9$k!%(B
$B%U%!%$%k%G%#%9%/%j%W%?(B 3 $B$r%/%m!<%:$9$k$3$H$K$h$j!$%U%!%$%k$O%U%!%$%k%G%#%9%/%j%W%?(B 0 $B$+$i$N$_%"%/%;%9$G$-$k$h$&$K$J$k!%(B

$B%W%m%0%i%`Nc(B

$B0J2<$O!$Bh(B1$B0z?t$K;XDj$5$l$?%U%!%$%k$r!$(Bwc $B$NI8=`F~NO$H$9$k%W%m%0%i%`$G$"$k!%(B 14$B!A(B19$B9TL\$GBh(B1$B0z?t$K;XDj$5$l$?%U%!%$%k$r(B open $B$9$k=hM}$r9T$C$F$$$k!%(B 21$B9TL\$G%U%!%$%k%G%#%9%/%j%W%?(B 0 $B$r%/%m!<%:$7!$:FMxMQ2DG=$J>uBV$K$7$F$$$k!%(B 22$B9TL\$G(B dup2 $B$r8F$S=P$7!$(B14$B9TL\$G%*!<%W%s$7$?%U%!%$%k$r%U%!%$%k%G%#%9%/%j%W%?(B 0 $B$+$i$b%"%/%;%9$G$-$k$h$&$K$7$F$$$k!%(B 23$B9TL\$G(B14$B9TL\$N%*!<%W%s$GuBV$K$J$k!%(B 25$B9TL\$G(B execlp $B$r8F$S!$(Bwc $B$r5/F0$7$F$$$k!%(B $B%U%!%$%k%G%#%9%/%j%W%?(B 0 $B$O(B14$B9TL\$G%*!<%W%s$7$?%U%!%$%k$H$D$J$,$C$F$$$k$?$a!$(Bwc $B$NI8=`F~NO$O$=$N%U%!%$%k$+$iFI$_9~$^$l$k$3$H$K$J$k!%(B

     1  #include <stdio.h>
     2  #include <fcntl.h>
     3
     4  void
     5  main(int argc, char *argv[])
     6  {
     7          int file_fd;
     8
     9          if (argc != 2) {
    10                  printf("Usage: %s file_name\n", argv[0]);
    11                  exit(1);
    12          }
    13
    14          file_fd = open(argv[1], O_RDONLY);
    15          if (file_fd < 0) {
    16                  perror("open");
    17                  close(file_fd);
    18                  exit(1);
    19          }
    20
    21          close(0);
    22          dup2(file_fd, 0);
    23          close(file_fd);
    24
    25          execlp("wc", "wc", NULL);
    26  }

$B0J2<$O!$>e5-%W%m%0%i%`$N

% ./a.out a.txt 
     38      38     374
%

$B%Q%$%W(B

$B35MW(B

$B%7%'%k$G%3%^%s%I$rl9g!$%Q%$%W5!G=$rMQ$$$k$3$H$G!$$"$k%3%^%s%I$N=PNO$rJL$N%3%^%s%I$NF~NO$H$9$k$3$H$,$G$-$k!%(B $BNc$($P0J2<$N$h$&$K(B ls $B$N7k2L$r(B wc $B$NF~NO$K$9$k$3$H$K$h$C$F!$8=:_$N%G%#%l%/%H%j$K$"$k%U%!%$%k$d%G%#%l%/%H%j$N?t$r?t$($k$3$H$,$G$-$k!%(B $B0J2<$NNc$G$O(B .c $B$G=*$o$k(BC$B%W%m%0%i%`%U%!%$%k$N?t$r?t$($F$$$k!%(B

% ls *.c | wc 
     38      38     374
%

$B%Q%$%W$r$b$&>/$7>\$7$/8+$F$_$k$H!$2

$B$3$N%Q%$%W$r$NDL$j(B pipe $B%7%9%F%`%3!<%k$G$"$k!%(B

int pipe(int filedes[2]);

pipe $B%7%9%F%`%3!<%k$r8F$V$H!$F~NO$H=PNO$=$l$>$l$N8}!J%U%!%$%k%G%#%9%/%j%W%?!K$r;}$D%Q%$%W$,(B1$BK\:n$i$l$k!%(B $B%U%!%$%k%G%#%9%/%j%W%?$O!$>e5-$NNc$@$H(B filedes $BG[Ns$K3JG<$5$l!$(Bfiledes[0] $B$,%Q%$%W$N=P8}!$(Bfiledes[1] $B$,%Q%$%W$NF~8}$N%U%!%$%k%G%#%9%/%j%W%?$K$J$k!%(B $B$3$N4X78$O!$%U%!%$%k%G%#%9%/%j%W%?(B 0 $B$,I8=`F~NO!$%U%!%$%k%G%#%9%/%j%W%?(B 1 $B$,I8=`=PNO$G$"$k$3$H$HBPHf$5$;$k$H$o$+$j$d$9$$!%(B $BB($A!$(Bfiledes[0] $B$+$iFI$_!$(Bfiledes[1] $B$K=q$/!%(B

$B%W%m%;%94V$N%Q%$%W$N:n@.$r?^<($9$k$H0J2<$N$h$&$K$J$k!%(B

pipe $B%7%9%F%`%3!<%k$r8F$V$H!$F~NO$H=PNO$=$l$>$l$N8}!J%U%!%$%k%G%#%9%/%j%W%?!K$r;}$D%Q%$%W$,(B1$BK\:n$i$l$k!%(B
$B$3$N>uBV$G(B fork $B$r8F$V$H!$%Q%$%W!JF~=PNO$N8}!K$,N>J}$H$b6&M-$5$l$?>uBV$K$J$k!%(B
$B0lJ}$N%W%m%;%9$,F~NO$r!$$b$&0lJ}$,=PNO$N8}$rJD$8$k$H!$%W%m%;%9$+$i%W%m%;%9$X%G!<%?$rAw$l$k!J%W%m%;%94VDL?.!K>uBV$K$J$k!%(B

$B%W%m%0%i%`Nc(B

$B0J2<$N(B$B%W%m%0%i%`(B$B$O!$%Q%$%W$r:n@.$7$?8e(B fork $B$r$7!$;R%W%m%;%9$+$i?F%W%m%;%9$XJ8;zNs$rAw$k%W%m%0%i%`$G$"$k!%(B

     1  #include <stdio.h>
     2
     3  int pipe_fd[2];
     4
     5  void
     6  do_child()
     7  {
     8          char    *p = "Hello, dad!!\n";
     9
    10          printf("this is child.\n");
    11
    12          close(pipe_fd[0]);
    13
    14          while (*p) {
    15                  if (write(pipe_fd[1], p, 1) < 0) {
    16                          perror("write");
    17                          exit(1);
    18                  }
    19                  p++;
    20          }
    21  }
    22
    23  void
    24  do_parent()
    25  {
    26          char    c;
    27          int     count, status;
    28
    29          printf("this is parent.\n");
    30
    31          close(pipe_fd[1]);
    32
    33          while ((count = read(pipe_fd[0], &c, 1)) > 0) {
    34                  putchar(c);
    35          }
    36
    37          if (count < 0) {
    38                  perror("read");
    39                  exit(1);
    40          }
    41
    42          if (wait(&status) < 0) {
    43                  perror("wait");
    44                  exit(1);
    45          }
    46  }
    47
    48  main()
    49  {
    50          int child;
    51
    52          if (pipe(pipe_fd) < 0) {
    53                  perror("pipe");
    54                  exit(1);
    55          }
    56
    57          if ((child = fork()) < 0) {
    58                  perror("fork");
    59                  exit(1);
    60          }
    61
    62          if (child)
    63                  do_parent();
    64          else
    65                  do_child();
    66  }

52$B9TL\$G%Q%$%W$r:n@.$7$?8e!$(B57$B9TL\$G(B fork $B$r$7$F$$$k!%(B
$B;R%W%m%;%9$O(B12$B9TL\$G%Q%$%W$N=P8}$r%/%m!<%:$7!$?F%W%m%;%9$O(B31$B9TL\$G%Q%$%W$NF~8}$r%/%m!<%:$9$k!%(B
$B;R%W%m%;%9$OJ8;zNs$r%Q%$%W$K=q$-9~$_!J(B14$B!A(B20$B9TL\!K!$?F%W%m%;%9$O$=$l$r%Q%$%W$+$iFI$_=P$9!J(B33$B!A(B35$B9TL\!K!%(B

$B$3$N%W%m%0%i%`$r%3%s%Q%$%k

% ./a.out 
this is parent.
this is child.
Hello, dad!!.
%

$B>e5-$N%W%m%0%i%`$r(B dup2 $B$r;HMQ$7!$I8=`F~=PNO$r%Q%$%W$G@\B3$9$k$H0J2<$N$h$&$K$J$k!%(B $B%Q%$%W$NITMW$J=PF~8}$N%/%m!<%:!J(B12, 30$B9TL\!K$H!$(Bdup2 $B$K$h$k%j%@%$%l%/%7%g%s$N$?$a$N%/%m!<%:!J(B14, 16, 32, 34$B9TL\!K$H!$$?$/$5$s%/%m!<%:$r8F$VI,MW$,$"$k!%(B

     1  #include <stdio.h>
     2
     3  int pipe_fd[2];
     4
     5  void
     6  do_child()
     7  {
     8          char    *p = "Hello, dad!!\n";
     9
    10          printf("this is child\n");
    11
    12          close(pipe_fd[0]);
    13
    14          close(1);
    15          dup2(pipe_fd[1], 1);
    16          close(pipe_fd[1]);
    17
    18          while (*p)
    19                  putchar(*p++);
    20  }
    21
    22  void
    23  do_parent()
    24  {
    25          char    c;
    26          int     count, status;
    27
    28          printf("this is parent\n");
    29
    30          close(pipe_fd[1]);
    31
    32          close(0);
    33          dup2(pipe_fd[0], 0);
    34          close(pipe_fd[0]);
    35
    36          while ((c = getchar()) != EOF)
    37                  putchar(c);
    38
    39          if (wait(&status) < 0) {
    40                  perror("wait");
    41                  exit(1);
    42          }
    43  }
    44
    45  main()
    46  {
    47          int child;
    48
    49          if (pipe(pipe_fd) < 0) {
    50                  perror("pipe");
    51                  exit(1);
    52          }
    53
    54          if ((child = fork()) < 0) {
    55                  perror("fork");
    56                  exit(1);
    57          }
    58
    59          if (child)
    60                  do_parent();
    61          else
    62                  do_child();
    63  }

$B%W%m%;%9$N:n@.$H/$J$/$H$b!$(Bfork$B$H(Bexecve$B$,J,$+$l$F$$$k$3$H$K$h$j!$%j%@%$%l%/%7%g%s$d%Q%$%W$,4JC1$K

$B$=$NB>$N%W%m%;%9A`:n$N$?$a$N%7%9%F%`%3!<%k!$%i%$%V%i%j4X?t(B

$B%W%m%;%96/@)=*N;(B

$BDL>o%W%m%;%9$r=*N;$9$k$?$a$K;HMQ$5$l$k(B kill $B%3%^%s%I$O!$(Bkill $B%7%9%F%`%3!<%k$r8F$V$3$H$G\$7$/=R$Y$k!%(B

int kill(pid_t pid, int sig);

$B%a%b%jNN0h3NJ](B

$BF0E*%a%b%jNN0h3NJ]$N$?$a$K$O!$DL>o%i%$%V%i%j4X?t$G$"$k(Bmalloc$BKt$O(Bcalloc$B$r;HMQ$9$k!%(B malloc $B$K$h$j3NJ]$5$l$kNN0h$N=i4|CM$OITDj$G$"$k!%(B calloc $B$O3NJ]$7$?NN0h$r(B 0 $B$K=i4|2=$9$k!%(B $BF0E*$J%a%b%jNN0h$O3NJ]$H3+J|$r7+$jJV$9$3$H$,B?$$!%(B $B$=$N$?$a!$(Bmalloc$BKt$O(Bcalloc$B$O2?$i$+$N%"%k%4%j%:%`$rMQ$$$F8zN($h$/%a%b%jNN0h$N:FMxMQ$r2DG=$K$7$F$$$k!%(B

malloc, calloc $B$G3NJ]$7$?NN0h$,ITMW$K$J$C$?$i!$(Bfree $B$K$h$j3+J|$9$k!%(B malloc, calloc $B$GNN0h3NJ]$r$7$F!$ITMW$K$J$C$F$b3+J|$7$J$$$^$^$GJ|CV$7$F$*$/$H!$:G=*E*$K$O;HMQ2DG=$J%a%b%jNL$rD6$($F!$%W%m%0%i%`$O0J>e=*N;$7$F$7$^$&!%(B $BFC$K!$3NJ]$7$?NN0h$X$N%]%$%s%?$r<:$C$F$7$^$$3+J|$G$-$J$/$J$C$F$7$^$&%P%0$O%a%b%j!<%j!<%/$H8F$P$l!$H/8+$7Fq$$%P%0$N0l$D$G$"$k!%(B

void *calloc(size_t nmemb, size_t size);
void *malloc(size_t size);
void free(void *ptr);
void *realloc(void *ptr, size_t size);

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int  brk(void *end_data_segment);
void *sbrk(ptrdiff_t increment);

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FILE *popen(const char *command, const char *type);
int pclose(FILE *stream);
int system (const char * string);

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int nice(int inc);
int getrlimit(int resource, struct rlimit *rlim);
int getrusage(int who, struct rusage *usage);
int setrlimit(int resource, const struct rlimit *rlim);
int ptrace(int request, int pid, int addr, int data);

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% ./a.out 
environ:        0xbfffe8dc
argv:           0xbfffe8d4
stack:          0xbfffe867
bss:            0x080496e8
data:           0x080495f0
% ./a.out 
environ:        0xbfffe6dc
argv:           0xbfffe6d4
stack:          0xbfffe667
bss:            0x080496e8
data:           0x080495f0
% ./a.out 
environ:        0xbfffe7dc
argv:           0xbfffe7d4
stack:          0xbfffe767
bss:            0x080496e8
data:           0x080495f0
%

$BN}=,LdBj!J#2#5!K(B

$B0J2<$N%W%m%0%i%`$r%3%s%Q%$%k!$

     1  #include <stdio.h>
     2
     3  main()
     4  {
     5          fork();
     6          fork();
     7          fork();
     8          printf("hello\n");
     9  }

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     1  #include <stdio.h>
     2  #include <stdlib.h>
     3
     4  main()
     5  {
     6          system("ls *.c | wc");
     7  }

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% ./if-then-else "test 1 -eq 1" "echo yes" "echo no" 
yes
% ./if-then-else "test 1 -eq 2" "echo yes" "echo no" 
no
%

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% ./if-then-else test 1 -eq 1 then echo yes else echo no

$BN}=,LdBj!J#2#9!K(B

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% ./a.out 30 
0A1B2C3D4E5F6G7H8I9J0K1L2M3N4O5P6Q7R8S9T0U1V2W3X4Y5Z6A7B8C9D
%

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     1  #include <stdio.h>
     2
     3  int pipe_fd[2];
     4
     5  void
     6  do_parent()
     7  {
     8          char    *p = "Hello, my kid.";
     9          int     status;
    10
    11          printf("this is parent.\n");
    12
    13          close(pipe_fd[0]);
    14
    15          while (*p) {
    16                  if (write(pipe_fd[1], p, 1) < 0) {
    17                          perror("write");
    18                          exit(1);
    19                  }
    20                  p++;
    21          }
    22
    23          if (wait(&status) < 0) {
    24                  perror("wait");
    25                  exit(1);
    26          }
    27  }
    28
    29  void
    30  do_child()
    31  {
    32          char    c;
    33          int     count;
    34
    35          printf("this is child.\n");
    36
    37          close(pipe_fd[1]);
    38
    39          while ((count = read(pipe_fd[0], &c, 1)) > 0) {
    40                  putchar(c);
    41          }
    42          putchar('\n');
    43
    44          if (count < 0) {
    45                  perror("read");
    46                  exit(1);
    47          }
    48  }
    49
    50  main()
    51  {
    52          int child;
    53
    54          if (pipe(pipe_fd) < 0) {
    55                  perror("pipe");
    56                  exit(1);
    57          }
    58
    59          if ((child = fork()) < 0) {
    60                  perror("fork");
    61                  exit(1);
    62          }
    63
    64          if (child)
    65                  do_parent();
    66          else
    67                  do_child();
    68  }

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