struct cmd*
parseexec(char **ps, char *es)
{
char *q, *eq;
int tok, argc;
struct execcmd *cmd;
struct cmd *ret;
ret = execcmd();
cmd = (struct execcmd*)ret;
argc = 0;
ret = parseredirs(ret, ps, es);
while(!peek(ps, es, "|")){
if((tok=gettoken(ps, es, &q, &eq)) == 0)
break;
if(tok != 'a') {
fprintf(stderr, "syntax error\n");
exit(-1);
}
cmd->argv[argc] = mkcopy(q, eq);
argc++;
if(argc >= MAXARGS) {
fprintf(stderr, "too many args\n");
exit(-1);
}
ret = parseredirs(ret, ps, es);
}
cmd->argv[argc] = 0;
return ret;
}
struct cmd*
parseredirs(struct cmd *cmd, char **ps, char *es)
{
int tok;
char *q, *eq;
while(peek(ps, es, "<>")){
tok = gettoken(ps, es, 0, 0);
if(gettoken(ps, es, &q, &eq) != 'a') {
fprintf(stderr, "missing file for redirection\n");
exit(-1);
}
switch(tok){
case '<':
cmd = redircmd(cmd, mkcopy(q, eq), '<');
break;
case '>':
cmd = redircmd(cmd, mkcopy(q, eq), '>');
break;
}
}
return cmd;
}
/*
按字面意思理解应该是分析重定向行为的函数
*/
struct cmd*
parseredirs(struct cmd *cmd, char **ps, char *es)
{
int tok;
char *q, *eq;
while(peek(ps, es, "<>")){ //去掉前导空白符，并且判断该字符串的首字符是否是<>中的一种
tok = gettoken(ps, es, 0, 0); //如果存在 <> 符号，那么定位这个 <> 符号左面的那个指令 如 $， ps
if(gettoken(ps, es, &q, &eq) != 'a') {
fprintf(stderr, "missing file for redirection\n");
exit(-1);
}
switch(tok){
case '<':
cmd = redircmd(cmd, mkcopy(q, eq), '<');
break;
case '>':
cmd = redircmd(cmd, mkcopy(q, eq), '>');
break;
}
}
return cmd;
}