shell. The contents
are:
smsh.c:
/** smsh1.c small-shell version 1
** first really useful version after prompting shell
** this one parses the command line into strings
** uses fork, exec, wait, and ignores signals
**/
#include
#include
#include
#include
#include "smsh.h"
#define DFL_PROMPT "> "
int main()
{
char *cmdline, *prompt, **arglist;
int result;
void setup();
prompt = DFL_PROMPT ;
setup();
while ( (cmdline = next_cmd(prompt, stdin)) !=
NULL ){
if ( (arglist = splitline(cmdline)) !=
NULL ){
result = execute(arglist);
freelist(arglist);
}
free(cmdline);
}
return 0;
}
void setup()
/*
* purpose: initialize shell
* returns: nothing. calls fatal() if trouble
*/
{
signal(SIGINT, SIG_IGN);
signal(SIGQUIT, SIG_IGN);
}
void fatal(char *s1,
char *s2, int n)
{
fprintf(stderr,"Error: %s,%s\n", s1, s2);
exit(n);
}
smsh.h:
#define YES 1
#define NO 0
char *next_cmd();
char **splitline(char *);
void freelist(char **);
void *emalloc(size_t);
void *erealloc(void *,
size_t);
int execute(char **);
void fatal(char *,
char *, int );
int process();
execute.c:
/* execute.c - code used by small shell to execute commands
*/
#include
#include
#include
#include
#include
int execute(char *argv[])
/*
* purpose: run a program passing it arguments
* returns: status returned via wait, or -1 on error
* errors: -1 on fork() or wait() errors
*/
{
int pid ;
int child_info = -1;
if ( argv[0] == NULL ) /*
nothing succeeds */
return 0;
if ( (pid = fork()) == -1 )
perror("fork");
else if ( pid == 0 ){
signal(SIGINT, SIG_DFL);
signal(SIGQUIT, SIG_DFL);
execvp(argv[0], argv);
perror("cannot execute command");
exit(1);
}
else {
if ( wait(&child_info) == -1 )
perror("wait");
}
return child_info;
}
splitline.c:
/* splitline.c - commmand reading and parsing functions for
smsh
*
* char *next_cmd(char *prompt, FILE *fp) - get next command
* char **splitline(char *str); - parse a string
*/
#include
#include
#include
#include "smsh.h"
char * next_cmd(char *prompt,
FILE *fp)
/*
* purpose: read next command line from fp
* returns: dynamically allocated string holding command line
* errors: NULL at EOF (not really an error)
* calls fatal from emalloc()
* notes: allocates space in BUFSIZ chunks.
*/
{
char *buf ; /* the buffer */
int bufspace = 0; /* total size */
int pos = 0; /* current position */
int c; /* input char */
printf("%s", prompt); /* prompt user */
while( ( c = getc(fp)) != EOF ) {
/* need space? */
if( pos+1 >= bufspace ){ /* 1 for \0 */
if ( bufspace == 0 ) /* y: 1st time */
buf = emalloc(BUFSIZ);
else /* or expand */
buf = erealloc(buf,bufspace+BUFSIZ);
bufspace += BUFSIZ; /* update size */
}
/* end of command? */
if ( c == '\n' )
break;
/* no, add to buffer */
buf[pos++] = c;
}
if ( c == EOF && pos == 0 ) /* EOF and
no input */
return NULL; /* say so */
buf[pos] = '\0';
return buf;
}
/**
** splitline ( parse a line into an array of strings )
**/
#define is_delim(x) ((x)==' '||(x)=='\t')
char ** splitline(char
*line)
/*
* purpose: split a line into array of white-space separated
tokens
* returns: a NULL-terminated array of pointers to copies of the
tokens
* or NULL if line if no tokens on the line
* action: traverse the array, locate strings, make copies
* note: strtok() could work, but we may want to add quotes
later
*/
{
char *newstr();
char **args ;
int spots = 0; /* spots in table */
int bufspace = 0; /* bytes in table */
int argnum = 0; /* slots used */
char *cp = line; /* pos in string */
char *start;
int len;
if ( line == NULL ) /* handle
special case */
return NULL;
args = emalloc(BUFSIZ); /* initialize array */
bufspace = BUFSIZ;
spots = BUFSIZ/sizeof(char
*);
while( *cp != '\0' )
{
while ( is_delim(*cp) ) /* skip leading spaces
*/
cp++;
if ( *cp == '\0' ) /* quit at end-o-string
*/
break;
/* make sure the array has room (+1 for NULL) */
if ( argnum+1 >= spots ){
args = erealloc(args,bufspace+BUFSIZ);
bufspace += BUFSIZ;
spots += (BUFSIZ/sizeof(char
*));
}
/* mark start, then find end of word */
start = cp;
len = 1;
while (*++cp != '\0' &&
!(is_delim(*cp)) )
len++;
args[argnum++] = newstr(start, len);
}
args[argnum] = NULL;
return args;
}
/*
* purpose: constructor for strings
* returns: a string, never NULL
*/
char *newstr(char *s,
int l)
{
char *rv = emalloc(l+1);
rv[l] = '\0';
strncpy(rv, s, l);
return rv;
}
void
freelist(char **list)
/*
* purpose: free the list returned by splitline
* returns: nothing
* action: free all strings in list and then free the list
*/
{
char **cp = list;
while( *cp )
free(*cp++);
free(list);
}
void * emalloc(size_t n)
{
void *rv ;
if ( (rv = malloc(n)) == NULL
)
fatal("out of memory","",1);
return rv;
}
void * erealloc(void *p,
size_t n)
{
void *rv;
if ( (rv = realloc(p,n)) ==
NULL )
fatal("realloc() failed","",1);
return rv;
}
QUESTION 1:
- The Contents Of The File Are C Sources That Implement A Simple Shell The Contents Are Smsh C Smsh1 C Small Shell 1 (280.52 KiB) Viewed 68 times