USP Lab Manual

Unix System Programming And Compiler Design Laboratory ( 10CSL68 )

Lab Manual Program 1: Write a C/C++ POSIX compliant program to check the following limits: (i) No. of clock ticks (ii) Max. no. of child processes (iii) Max. path length (iv) Max. no. of characters in a file name (v) Max. no. of open files/ process #define _POSIX_SOURCE #include #include #include #include using namespace std; int main() { long ret; if((ret=pathconf("/",_PC_PATH_MAX))==-1) { perror("pathconf"); return -1; } else cout<<"Maximum Path Length = "<
Dept of CSE, PESIT Bangalore South Campus.

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Unix System Programming And Compiler Design Laboratory ( 10CSL68 ) cout<<"chown restricted option is: "<<_POSIX_CHOWN_RESTRICTED<
Program 3 :Consider the last 100 bytes as a region. Write a C/C++ program to check whether the region is locked or not. If the region is locked, print pid of the process which has locked. If the region is not locked, lock the region with an exclusive lock, read the last 50 bytes and unlock the region. #include #include #include #include #include #include using namespace std; int main(int argc, char** argv) { int fd; struct flock fLock; char buf[80]; if((fd=open(argv[1],O_RDWR))==-1) { perror("open"); Dept of CSE, PESIT Bangalore South Campus.

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Unix System Programming And Compiler Design Laboratory ( 10CSL68 ) return -1; } //Set lock parameters fLock.l_type=F_WRLCK; fLock.l_whence=SEEK_END; fLock.l_start=-100; fLock.l_len=100;

/* Attempt to set an exclusive lock on a File */ while(fcntl(fd,F_SETLK,&fLock)==-1) { /* Set Lock Fails, find out who had locked the file */ while((fcntl(fd,F_GETLK,&fLock)!=-1)) { cout << endl << argv[1] << " is Locked by the Process " << fLock.l_pid << " from " << fLock.l_start << " for " << fLock.l_len << " bytes for " << (fLock.l_type==F_WRLCK?"write":"read") << endl; return 1; } } cout << "\nLock aquired on the File " << argv[1] << " by process with ID " << getpid() << endl; sleep(30); lseek(fd,-50,SEEK_END); if(read(fd,buf,50)==-1) { perror("read"); } else { cout << "\nReading 50 bytes from file\n"; cout << buf; cout << endl; } fLock.l_type = F_UNLCK; fLock.l_whence = SEEK_SET; fLock.l_start = 0; fLock.l_len = 0; if(fcntl(fd,F_SETLKW,&fLock)==-1) perror("fcntl"); else cout << endl << argv[1] << " unlocked by process " << getpid() << endl; return 0; }


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Program 4 :Write a C/C++ program which demonstrates interprocess communication between a reader process and a writer process. Use mkfifo, open, read, write and close APIs in your program. /*File

: reader_ipcomm.c

*/

#include #include #include #include #include #include #include #include #define FIFO_NAME "MY_FIFO" int main(void) { char s[300]; int num, fd; // mknod(FIFO_NAME, S_IFIFO|0666, 0); mkfifo(FIFO_NAME, S_IFIFO|S_IRWXU|S_IRWXG|S_IRWXO); printf("Waiting for Writers... \n"); fd=open(FIFO_NAME, O_RDONLY); printf("Got a Writer...\n"); do { if((num=read(fd,s,300))==-1) { perror("read"); } else { s[num]='\0'; printf("Receiver:Read %d bytes: \"%s\" \n",num,s); } }while(num>0); return 0; }

/*File

#include #include #include #include #include

: writer_ipcomm.c */


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Unix System Programming And Compiler Design Laboratory ( 10CSL68 ) #include #include #include #define FIFO_NAME "MY_FIFO" int main(void) { char s[300]; int num, fd; // mknod(FIFO_NAME, S_IFIFO|0666, 0); mkfifo(FIFO_NAME, S_IFIFO|S_IRWXU|S_IRWXG|S_IRWXO); printf("Waiting for Readers... \n"); fd=open(FIFO_NAME, O_WRONLY); printf("Got a Reader... type Something: \n"); while(gets(s), !feof(stdin)) { if((num=write(fd,s,strlen(s)))==-1) { perror("write"); } else { printf("Writer: wrote %d bytes \n",num); } } return 0; }

Program 5a :Write a C / C++ program to emulate the unix ln command #include #include #include #include #include int main(int argc, char* argv[]) { int i,flag,rcode; char f1[256],f2[256],err[256]; if(argc<3) { printf("Syntax error:\n Usage Syntax: ./mylink [-s] file1 file2 \n"); return 0; } flag=strcmp(argv[1],"-s"); if(flag!=0) { Dept of CSE, PESIT Bangalore South Campus.

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Unix System Programming And Compiler Design Laboratory ( 10CSL68 ) { strcpy(f1,argv[1]); strcpy(f2,argv[2]); } rcode=link(f1,f2); if(rcode==0) { printf("Link Successfully created\n"); }

else { printf("Link creation failed: %d\n", errno); printf("error number is : %d \n", errno); strcpy(err, strerror(errno)); perror("ln"); puts(err); } } else { strcpy(f1,argv[2]); strcpy(f2,argv[3]); rcode=symlink(f1,f2); if(rcode==0) { printf("\n Soft link created successsfully \n"); } else { printf("Link creation failed: %d\n", errno); strcpy(err, strerror(errno)); puts(err); } } return 0; }

Program 5b :#include #include int main(char* argv[], int argc, char* envp[]) { int index=0; while(envp[index]) { printf("%s \n",envp[index++]);


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Unix System Programming And Compiler Design Laboratory ( 10CSL68 ) } return 0; }

Program 6 :Write a C/C++ program to illustrate the race condition. #include #include #include #include #include #include

static void charatatime(char *); int main() { pid_t pid, pid2; if((pid=fork())<0) { perror("fork"); return -1; } else if (pid==0) { charatatime("\n output from child \n"); } else { charatatime("\n output from parent \n"); } exit(0); } static void charatatime(char * str) { char *ptr; int c; setbuf(stdout, NULL); for(ptr=str; c=*ptr++;) { putc(c,stdout); } }

Program 7 :Dept of CSE, PESIT Bangalore South Campus.

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Write a C/C++ program that creates a zombie and then calls system to execute the ps command to verify that the process is zombie. #include #include #include #include #include int main() { pid_t pid,retpid; char cmd[50]; printf("Parent Process with process id %d starts...\n",getpid()); if((pid=fork())==-1) { perror("fork"); return -1; } else if(pid==0) { printf("Child Process Created\n"); printf("Child Pid:%d Parent Pid:%d\n",getpid(),getppid()); sleep(5); _exit(0); } else { sleep(20); printf("Parent Process Resumes Its Execution,,,,\n"); } return 0; }

Program 8 :Write a C/C++ program to avoid zombie process by forking twice. #include #include #include #include #include

int main() { pid_t pid1,pid2; printf("Parent process P starts... PID : %d \n", getpid());


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Unix System Programming And Compiler Design Laboratory ( 10CSL68 ) if((pid1=fork())==-1) //create P1 { perror("fork"); return -1; } else if(pid1==0) { printf("Child process P1 starts... PID : %d \n", getpid()); if((pid2=fork())==-1) { perror("fork"); return -1; } else if(pid2==0) { printf("Grand child P2 created... PID: %d \n", getpid()); sleep(10); } else //P1 exits leaving P2 orphan { exit(0); } } waitpid(pid1, NULL,0); sleep(10); return 0; }

Program 9 :Write a C/C++ program to implement the system function. #include #include #include int mysystem(const char* stringcmd) { int status; pid_t pid; if (stringcmd==NULL) { return 1; } if((pid=fork())==-1) { perror("fork"); status=-1; } else if (pid==0) { execl("/bin/sh","sh","-c", stringcmd, (char*)0); status=0; }


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Unix System Programming And Compiler Design Laboratory ( 10CSL68 ) else { while(waitpid(pid, &status,0)==-1) { perror("waitpid"); return -1; } } return status; } int main() { int status; char cmd[10]; do{ printf("My Shell>"); gets(cmd); if((status=mysystem(cmd))<0) printf("Error\n"); return -1; }while(strcmp(cmd,"exit")); return 0; }

Program 10 :Write a C/C++ program to set up a real-time clock interval timer using the alarm API. #include #include #include #include #include

void alarm_handler (int signum) { printf("\n Timer Hit! \n"); } void func(int duration) { struct itimerval delay; int ret; signal(SIGALRM, alarm_handler); delay.it_value.tv_sec=duration; delay.it_value.tv_usec=0; delay.it_interval.tv_sec=0; delay.it_interval.tv_usec=0; ret=setitimer(ITIMER_REAL, &delay, NULL); if(ret) {


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Unix System Programming And Compiler Design Laboratory ( 10CSL68 ) perror("setitimer"); return; } pause(); } int main() { int dur; printf("\n Enter duration for alarm \n"); scanf("%d", &dur); func(dur); return 0; }

Program 11 :Write a C program to implement the syntax-directed definition of “if E then S1” and “if E then S1 else S2”. #include #include #include char input[60], stmt[3][60]; int cur,len,i,j; void gen() { int L1=101,L2=102,L3=103; printf("if %s goto %d \n", stmt[0],L1); printf("\n goto %d \n", L2); printf("%d : %s \n", L1,stmt[1]); if(cur<3) { printf("%d : STOP \n",L2); } else { printf("goto %d \n",L3); printf("%d : %s \n", L2, stmt[2]); printf("%d : STOP \n",L3); } }

int main() { printf("format of if statement \n example: \n"); printf("if (a
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Unix System Programming And Compiler Design Laboratory ( 10CSL68 ) printf("Enter the statement \n"); gets(input); len=strlen(input); int index=0; for(i=0;i
Program 12 :Write a yacc program that accepts a regular expression as input and produce its parse tree as output. %{ #include #include #include #include #define max 100 int getreindex(const char *); signed char productions[max][max]; int count=0,i,j; char temp[max+max],temp2[max+max]; %} %token ALPHABET %left '|' %left '.' %nonassoc '*''+' %% S :re'\n' { printf("this is the rightmost derivation--\n"); for(i=count-1;i>=0;--i) { if(i==count-1) { printf("\nre-->"); strcpy(temp,productions[i]); printf("%s",productions[i]); } else { printf("\n-->");


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Unix System Programming And Compiler Design Laboratory ( 10CSL68 ) j=getreindex(temp); temp[j]='\0'; sprintf(temp2,"%s%s%s",temp,productions[i],(temp+j+2)); printf("%s",temp2); strcpy(temp,temp2); } } printf("\n"); exit(0); }

re: ALPHABET { temp[0]=yylval;temp[1]='\0'; strcpy(productions[count++],temp); } |'('re')' {strcpy(productions[count++],"(re)");} |re'*' {strcpy(productions[count++],"re*");} |re'+' {strcpy(productions[count++],"re+");} |re'|'re {strcpy(productions[count++],"re|re");} |re'.'re {strcpy(productions[count++],"re.re");} ; %% int main(int argc,char **argv) { yyparse(); return 0; } yylex() { signed char ch=getchar(); yylval=ch; if(isalpha(ch)) return ALPHABET; return ch; } yyerror() { fprintf(stderr,"invalid regular expression!\n"); exit(1); } int getreindex(const char *str) { int i=strlen(str)-1; for(;i>=0;i--) if(str[i]=='e' && str[i-1]=='r') return i-1; }


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