Script started on Wed Oct 23 12:33:49 2024
mweeks@air:Desktop$ ls pope*
popen_example.c
mweeks@air:Desktop$ gcc popen_example.c
mweeks@air:Desktop$ cat popen_example.c 
/* 
  Example of the popen/pclose command (process I/O).
  Get a list of files using the popen command.

  -MCW, Sept 2024
*/

#include <stdio.h>
#include <stdlib.h>     // defines "system", "exit"

#define BUFFER_SIZE 1024

int main (int argc, char *argv[]) {

  // myProcess is a stream that we will read from.
  // This is like reading input from the user, except that
  // the input is coming from a different "file".
  FILE *myProcess;
  // buffer is a place to store text. 
  // Instead of reading from the stream 1 char at a time, we 
  // read many of them, defined as BUFFER_SIZE above.
  char buffer[BUFFER_SIZE];
  int count = 0;

  printf("Here is a list of all files that end with .c\n");

  // List all files in the current dir that end with .c 
  // Open the stream
  myProcess = popen("ls *.c", "r");  // "r" for read
  // Always check to see if the command worked.
  if (myProcess == NULL) {
    // It did not work, so quit.
    printf("Error: ls *.c command failed\n");
    exit(1);
  }

  // Read up to BUFFER_SIZE-1 chars.
  fgets(buffer, BUFFER_SIZE, myProcess);
  // Check for end-of-file
  while (!feof(myProcess)) {
    count++;
    // Print it out
    // Notice that there is no \n since one is in the buffer
    printf("File %d is %s", count, buffer); 
    // get the next line
    fgets(buffer, BUFFER_SIZE, myProcess);
  }
  // Close the stream
  pclose(myProcess);


  return 0;
}
mweeks@air:Desktop$ ./a.out
Here is a list of all files that end with .c
File 1 is popen_example.c
mweeks@air:Desktop$ ./a.out
Here is a list of all files that end with .c
File 1 is fopen_example.c
File 2 is popen_example.c
mweeks@air:Desktop$ echo $? 
0
mweeks@air:Desktop$ echo $? 
0
mweeks@air:Desktop$ RV=$?
mweeks@air:Desktop$ echo $RV
0
mweeks@air:Desktop$ cd csc3320/programs/
mweeks@air:programs$ cd C_ch9
mweeks@air:C_ch9$ cat myexit.c
#include <stdio.h>
#include <stdlib.h> /* needed for exit */

int main() {
  printf("I am going to exit with status code 42\n");
  exit(42);
}
mweeks@air:C_ch9$ gcc myexit.c -o myexit
mweeks@air:C_ch9$ echo $?
0
mweeks@air:C_ch9$ ./myexit
I am going to exit with status code 42
mweeks@air:C_ch9$ echo $?
42
mweeks@air:C_ch9$ vi call_myexit.bash
mweeks@air:C_ch9$ ls -l call_myexit.bash 
-rw-r--r--  1 mweeks  staff  259 Oct 23 12:54 call_myexit.bash
mweeks@air:C_ch9$ chmod 700 call_myexit.bash 
mweeks@air:C_ch9$ ls -l call_myexit.bash 
-rwx------  1 mweeks  staff  259 Oct 23 12:54 call_myexit.bash
mweeks@air:C_ch9$ cat call_myexit.bash
#!/bin/bash
#
# This calls a program, and based on the return code, 
# issues an error or not.
# -MCW
#

    ./myexit
    if [ $? != 0 ]
    then
      echo "  Error -- the last command failed"
      exit 1
    else
      echo "  The command worked"
    fi


mweeks@air:C_ch9$ ./call_myexit.bash 
I am going to exit with status code 42
  Error -- the last command failed
mweeks@air:C_ch9$ cd ..
mweeks@air:programs$ cd C_ch13
mweeks@air:C_ch13$ ls
a.out			ch13_6.c		string_example.c
ch13_3.c		ch13_7.c		string_example2.c
ch13_4.c		ch13_8.c		test_string1.c
ch13_5.c		ch13_9.c		test_string2.c
mweeks@air:C_ch13$ grep strcpy *.c
ch13_4.c:        strncpy(str1, strcpy(str2, "abcd"), 4);
ch13_4.c:        char *strcpy(char * dest, const char * src); 
ch13_8.c:      strcpy(q,p); 
ch13_9.c:    strcpy(s1,"computer"); 
ch13_9.c:          strcpy(s2,"science"); 
string_example.c:    // strcpy -> strncpy
string_example.c:    // strcpy
string_example.c:    //strcpy(date1, date2);
string_example2.c:    // strcpy -> strncpy
string_example2.c:    // strcpy
string_example2.c:    //strcpy(date1, date2);
mweeks@air:C_ch13$ cat ch13_4.c
#include <stdio.h>

int main(){
    char str1[5]; char str2[] = "abcd";
        strncpy(str2, "abcd", 4); 
        strncpy(str1, str2, 4); 
        strncpy(str1, strcpy(str2, "abcd"), 4);
        char *strcpy(char * dest, const char * src); 

}
mweeks@air:C_ch13$ cp ch13_4.c ch13_4b.c
mweeks@air:C_ch13$ vi ch13_4b.c
mweeks@air:C_ch13$ cat ch13_4b.c
#include <stdio.h>
//#include <string.h>

int main(){
  char str1[5]; char str2[] = "abcd";
  //        strncpy(str2, "abcd", 4); 
  strncpy(str1, str2, 4); 
  //    strncpy(str1, strcpy(str2, "abcd"), 4);
  //    char *strcpy(char * dest, const char * src); 
  printf("str1 is [%s]\n", str1);

  return 0;
}
mweeks@air:C_ch13$ gcc ch13_4b.c
ch13_4b.c:7:3: warning: implicitly declaring library function 'strncpy' with
      type 'char *(char *, const char *, unsigned long)'
      [-Wimplicit-function-declaration]
  strncpy(str1, str2, 4); 
  ^
ch13_4b.c:7:3: note: include the header <string.h> or explicitly provide a
      declaration for 'strncpy'
1 warning generated.
mweeks@air:C_ch13$ vi ch13_4b.c
mweeks@air:C_ch13$ gcc ch13_4b.c
mweeks@air:C_ch13$ cat ch13_4b.c
#include <stdio.h>
#include <string.h>

int main(){
  char str1[5]; char str2[] = "abcd";
  //        strncpy(str2, "abcd", 4); 
  strncpy(str1, str2, 4); 
  //    strncpy(str1, strcpy(str2, "abcd"), 4);
  //    char *strcpy(char * dest, const char * src); 
  printf("str1 is [%s]\n", str1);

  return 0;
}
mweeks@air:C_ch13$ ./a.out
str1 is [abcd]
mweeks@air:C_ch13$ cp ch13_4b.c ch13_4c.c
mweeks@air:C_ch13$ vi ch13_4c.c
mweeks@air:C_ch13$ cat ch13_4c.c
#include <stdio.h>
#include <string.h>

int main(){
  char str1[5]; char str2[] = "abcd";

  strncpy(str1, "abcd", 4); 
  //strncpy(str1, str2, 4); 
  printf("str1 is [%s]\n", str1);

  return 0;
}
mweeks@air:C_ch13$ gcc ch13_4c.c
mweeks@air:C_ch13$ ./a.out
str1 is [abc]
mweeks@air:C_ch13$ vi ch13_4c.c
mweeks@air:C_ch13$ gcc ch13_4c.c
mweeks@air:C_ch13$ ./a.out
str1 is [abcd]
str[0] = 97 a
str[1] = 98 b
str[2] = 99 c
str[3] = 100 d
str[4] = 16 
mweeks@air:C_ch13$ mv ch13_4c.c ch13_4c_bad.c
mweeks@air:C_ch13$ cp ch13_4c_bad.c ch13_4c_good.c
mweeks@air:C_ch13$ vi ch13_4c_good.c
mweeks@air:C_ch13$ cpp ch13_4c_good.c
# 1 "ch13_4c_good.c"
# 1 "<built-in>" 1
# 1 "<built-in>" 3
# 360 "<built-in>" 3
# 1 "<command line>" 1
# 1 "<built-in>" 2
# 1 "ch13_4c_good.c" 2
# 1 "/usr/include/stdio.h" 1 3 4
# 22 "/usr/include/stdio.h" 3 4
[Thousands of lines deleted] 
  __builtin___strncpy_chk (str1,  "abcd", 4, __builtin_object_size (str1, 2 > 1 ? 1 : 0)); 
  
  //__builtin___strncpy_chk (str1,  str2, 4, __builtin_object_size (str1, 2 > 1 ? 1 : 0)); 
  printf("str1 is [%s]\n", str1);

  for (int i=0; i<strlen(str1); i++) {
    printf("str[%d] = %d %c\n", i, str1[i], str1[i]);
  }

  return 0;
}

20 errors generated.
mweeks@air:C_ch13$ vi ch13_4c_good.c
mweeks@air:C_ch13$ cpp ch13_4c_good.c
mweeks@air:C_ch13$ which cpp
/usr/bin/cpp
mweeks@air:C_ch13$ gcc ch13_4c_good.c
mweeks@air:C_ch13$ ./a.out
str1 is [abcd]
str[0] = 97 a
str[1] = 98 b
str[2] = 99 c
str[3] = 100 d
mweeks@air:C_ch13$ cpp ch13_4c_good.c
[Lines deleted]
mweeks@air:C_ch13$ vi ch13_4c_good.c
mweeks@air:C_ch13$ gcc ch13_4c_good.c
mweeks@air:C_ch13$ ./a.out
str1 is [abcd]
str[0] = 97 a
str[1] = 98 b
str[2] = 99 c
str[3] = 100 d
mweeks@air:C_ch13$ cat ch13_4c_good.c
#include <stdio.h>
#include <string.h>

int main(){
  char str1[5] = {0};
;  char str2[] = "abcd";

  strncpy(str1, "abcd", 4); 
  
  //strncpy(str1, str2, 4); 
  printf("str1 is [%s]\n", str1);

  for (int i=0; i<strlen(str1); i++) {
    printf("str[%d] = %d %c\n", i, str1[i], str1[i]);
  }

  return 0;
}
mweeks@air:C_ch13$ cp ch13_4c_good.c ch13_4d.c
mweeks@air:C_ch13$ vi ch13_4d.c 
mweeks@air:C_ch13$ gcc ch13_4d.c
mweeks@air:C_ch13$ cat ch13_4d.c
#include <stdio.h>
#include <string.h>

int main(){
  char str1[100] = {0};
  //char str2[] = "abcd";

  strncpy(str1, "abcd", 4); 
  strncat(str1, "efg", 7); 
 
  //strncpy(str1, str2, 4); 
  printf("str1 is [%s]\n", str1);

  for (int i=0; i<strlen(str1); i++) {
    printf("str[%d] = %d %c\n", i, str1[i], str1[i]);
  }

  return 0;
}
mweeks@air:C_ch13$ ./a.out
str1 is [abcdefg]
str[0] = 97 a
str[1] = 98 b
str[2] = 99 c
str[3] = 100 d
str[4] = 101 e
str[5] = 102 f
str[6] = 103 g
mweeks@air:C_ch13$ cp ch13_4d.c ch13_4e.c
mweeks@air:C_ch13$ vi ch13_4e.c
mweeks@air:C_ch13$ gcc ch13_4e.c
mweeks@air:C_ch13$ cat ch13_4e.c
#include <stdio.h>
#include <string.h>

int main(){
  char str1[100] = {0};
  //char str2[] = "abcd";

  strncpy(str1, "abcd", 4); 
  strncat(str1, "efg", 7); 
 
  //strncpy(str1, str2, 4); 
  printf("str1 is [%s]\n", str1);

  for (int i=0; i<strlen(str1); i++) {
    printf("str[%d] = %d %c\n", i, str1[i], str1[i]);
  }

  if (strncmp(str1, "Abcdefg", 7))
    printf("Equal\n");
  else
    printf("Not Equal\n");


  return 0;
}
mweeks@air:C_ch13$ ./a.out
str1 is [abcdefg]
str[0] = 97 a
str[1] = 98 b
str[2] = 99 c
str[3] = 100 d
str[4] = 101 e
str[5] = 102 f
str[6] = 103 g
Equal
mweeks@air:C_ch13$ man strncmp
mweeks@air:C_ch13$ cp ch13_4e.c ch13_4e_bad.c
mweeks@air:C_ch13$ vi ch13_4e.c
mweeks@air:C_ch13$ cat ch13_4e.c
#include <stdio.h>
#include <string.h>

int main(){
  char str1[100] = {0};
  //char str2[] = "abcd";

  strncpy(str1, "abcd", 4); 
  strncat(str1, "efg", 7); 
 
  //strncpy(str1, str2, 4); 
  printf("str1 is [%s]\n", str1);

  for (int i=0; i<strlen(str1); i++) {
    printf("str[%d] = %d %c\n", i, str1[i], str1[i]);
  }

  if (strncmp(str1, "abcdefg", 7) == 0)
    printf("Equal\n");
  else
    printf("Not Equal\n");


  return 0;
}
mweeks@air:C_ch13$ gcc ch13_4e.c
mweeks@air:C_ch13$ ./a.out
str1 is [abcdefg]
str[0] = 97 a
str[1] = 98 b
str[2] = 99 c
str[3] = 100 d
str[4] = 101 e
str[5] = 102 f
str[6] = 103 g
Equal
mweeks@air:C_ch13$ 
mweeks@air:C_ch13$ 
mweeks@air:C_ch13$ man strnlen
mweeks@air:C_ch13$ xxd a.out
00000000: cffa edfe 0700 0001 0300 0080 0200 0000  ................
00000010: 0f00 0000 0005 0000 8500 2000 0000 0000  .......... .....
00000020: 1900 0000 4800 0000 5f5f 5041 4745 5a45  ....H...__PAGEZE
00000030: 524f 0000 0000 0000 0000 0000 0000 0000  RO..............
[Many lines deleted]
000021f0: 6d68 5f65 7865 6375 7465 5f68 6561 6465  mh_execute_heade
00002200: 7200 5f6d 6169 6e00 5f5f 5f73 7461 636b  r._main.___stack
00002210: 5f63 686b 5f66 6169 6c00 5f5f 5f73 7461  _chk_fail.___sta
00002220: 636b 5f63 686b 5f67 7561 7264 005f 5f5f  ck_chk_guard.___
00002230: 7374 726e 6361 745f 6368 6b00 5f5f 5f73  strncat_chk.___s
00002240: 7472 6e63 7079 5f63 686b 005f 6d65 6d73  trncpy_chk._mems
00002250: 6574 005f 7072 696e 7466 005f 7374 726c  et._printf._strl
00002260: 656e 005f 7374 726e 636d 7000 6479 6c64  en._strncmp.dyld
00002270: 5f73 7475 625f 6269 6e64 6572 0000 0000  _stub_binder....
00002280: 0000 0000                                ....
mweeks@air:C_ch13$ man xxd
mweeks@air:C_ch13$ 
mweeks@air:C_ch13$ exit
exit

Script done on Wed Oct 23 13:45:50 2024