Linux编程实践教程》之Shell编程二

《Unix/Linux编程实践教程》第九章将第八章所编的shell做进一步的完善，包括：1）加入命令行解析，方便用户在一行里输完命令和所有参数2）加入if..else..控制语句3）加入局部变量和环境变量对于上章后面的练习题（解决SIGINT信号杀死shell的BUG），本章也给出了解决方案,简单流程如下：在shell中忽略SIGINT和SIGQUIT，在子进程中对恢复信号的默认操作。相关阅读：《Unix/Linux编程实践教程》之Shell编程一 http://www.linuxidc.com/Linux/2012-12/75690.htm《Unix/Linux编程实践教程》之Shell编程二 http://www.linuxidc.com/Linux/2012-12/75691.htm《Unix/Linux编程实践教程》之管道 http://www.linuxidc.com/Linux/2012-12/75692.htmUnix/Linux编程实践教程【高清PDF中文版+附录光盘+代码】：http://www.linuxidc.com/Linux/2011-08/41374.htm代码如下，一共4个文件：smsh.h:1: #defineYES12: #defineNO03: 4: char*next_cmd（）;5: char**splitline（char *）;6: voidfreelist（char **）;7: void*emalloc（size_t）;8: void*erealloc（void *, size_t）;9: intexecute（char **）; 10: voidfatal（char *, char *, int ）; 11:12: intprocess（）;smsh1.c:1: /**smsh1.csmall-shell version 12:**first really useful version after prompting shell3:**this one parses the command line into strings4:**uses fork, exec, wait, and ignores signals5:**/6: 7: #include<stdio.h>8: #include<stdlib.h>9: #include<unistd.h> 10: #include<signal.h> 11: #include"smsh.h" 12:13: #defineDFL_PROMPT"> " 14:15: int main（） 16: { 17: char*cmdline, *prompt, **arglist; 18: intresult; 19: voidsetup（）; 20:21: prompt = DFL_PROMPT ; 22: setup（）; 23:24: while （（cmdline = next_cmd（prompt, stdin））！= NULL ）{ 25: if （（arglist = splitline（cmdline））！= NULL）{ 26: result = execute（arglist）; 27: freelist（arglist）; 28: } 29: free（cmdline）; 30: } 31: return 0; 32: } 33:34: void setup（） 35: /* 36:* purpose: initialize shell 37:* returns: nothing. calls fatal（） if trouble 38:*/ 39: { 40: signal（SIGINT,SIG_IGN）; 41: signal（SIGQUIT, SIG_IGN）; 42: } 43:44: void fatal（char *s1, char *s2, int n） 45: { 46: fprintf（stderr,"Error: %s,%s/n", s1, s2）; 47: exit（n）; 48: } 49:50: splitline.c:1: /* splitline.c - commmand reading and parsing functions for smsh2:*3:*char *next_cmd（char *prompt, FILE *fp） - get next command4:*char **splitline（char *str）; - parse a string5: 6:*/7: 8: #include<stdio.h>9: #include<stdlib.h> 10: #include<string.h> 11: #include"smsh.h" 12:13: char * next_cmd（char *prompt, FILE *fp） 14: /* 15:* purpose: read next command line from fp 16:* returns: dynamically allocated string holding command line 17:*errors: NULL at EOF （not really an error） 18:*calls fatal from emalloc（） 19:* notes: allocates space in BUFSIZ chunks. 20:*/ 21: { 22: char*buf ; /* the buffer*/ 23: intbufspace = 0;/* total size*/ 24: intpos = 0;/* current position*/ 25: intc;/* input char*/ 26:27: printf（"%s", prompt）;/* prompt user*/ 28: while（（ c = getc（fp））！= EOF ） { 29:30: /* need space？ */ 31: if（ pos+1 >= bufspace ）{/* 1 for /0*/ 32: if （ bufspace == 0 ）/* y: 1st time*/ 33: buf = emalloc（BUFSIZ）; 34: else/* or expand*/ 35: buf = erealloc（buf,bufspace+BUFSIZ）; 36: bufspace += BUFSIZ;/* update size*/ 37: } 38:39: /* end of command？ */ 40: if （ c == "/n" ） 41: break; 42:43: /* no, add to buffer */ 44: buf[pos++] = c; 45: } 46: if （ c == EOF && pos == 0 ）/* EOF and no input*/ 47: return NULL;/* say so*/ 48: buf[pos] = "/0"; 49: return buf; 50: } 51:52: /** 53:**splitline （ parse a line into an array of strings ） 54:**/ 55: #defineis_delim（x）（（x）==" "||（x）=="/t"） 56:57: char ** splitline（char *line） 58: /* 59:* purpose: split a line into array of white-space separated tokens 60:* returns: a NULL-terminated array of pointers to copies of the tokens 61:*or NULL if line if no tokens on the line 62:*action: traverse the array, locate strings, make copies 63:*note: strtok（） could work, but we may want to add quotes later 64:*/ 65: { 66: char*newstr（）; 67: char**args ; 68: intspots = 0;/* spots in table*/ 69: intbufspace = 0;/* bytes in table*/ 70: intargnum = 0;/* slots used*/ 71: char*cp = line;/* pos in string*/ 72: char*start; 73: intlen; 74:75: if （ line == NULL ）/* handle special case*/ 76: return NULL; 77:78: args = emalloc（BUFSIZ）;/* initialize array*/ 79: bufspace = BUFSIZ; 80: spots= BUFSIZ/sizeof（char *）; 81:82: while（ *cp ！= "/0" ） 83: { 84: while （ is_delim（*cp））/* skip leading spaces*/ 85: cp++; 86: if （ *cp == "/0" ）/* quit at end-o-string*/ 87: break; 88:89: /* make sure the array has room （+1 for NULL） */ 90: if （ argnum+1 >= spots ）{ 91: args = erealloc（args,bufspace+BUFSIZ）; 92: bufspace += BUFSIZ; 93: spots += （BUFSIZ/sizeof（char *））; 94: } 95:96: /* mark start, then find end of word */ 97: start = cp; 98: len = 1; 99: while （*++cp ！= "/0" && ！（is_delim（*cp）））100: len++;101: args[argnum++] = newstr（start, len）;102: }103: args[argnum] = NULL;104: return args;105: }106: 107: /*108:* purpose: constructor for strings109:* returns: a string, never NULL110:*/111: char *newstr（char *s, int l）112: {113: char *rv = emalloc（l+1）;114: 115: rv[l] = "/0";116: strncpy（rv, s, l）;117: return rv;118: }119: 120: void 121: freelist（char **list）122: /*123:* purpose: free the list returned by splitline124:* returns: nothing125:*action: free all strings in list and then free the list126:*/127: {128: char**cp = list;129: while（ *cp ）130: free（*cp++）;131: free（list）;132: }133: 134: void * emalloc（size_t n）135: {136: void *rv ;137: if （（rv = malloc（n）） == NULL ）138: fatal（"out of memory","",1）;139: return rv;140: }141: void * erealloc（void *p, size_t n）142: {143: void *rv;144: if （（rv = realloc（p,n）） == NULL ）145: fatal（"realloc（） failed","",1）;146: return rv;147: }148: 149: execute.c:1: /* execute.c - code used by small shell to execute commands */2: 3: #include<stdio.h>4: #include<stdlib.h>5: #include<unistd.h>6: #include<signal.h>7: #include8: 9: int execute（char *argv[]） 10: /* 11:* purpose: run a program passing it arguments 12:* returns: status returned via wait, or -1 on error 13:*errors: -1 on fork（） or wait（） errors 14:15:*/ 16: { 17: intpid ; 18: intchild_info = -1; 19:20: if （ argv[0] == NULL ）/* nothing succeeds*/ 21: return 0; 22:23: if （（pid = fork（））== -1 ） 24: perror（"fork"）; 25: else if （ pid == 0 ）{ 26: signal（SIGINT, SIG_DFL）; 27: signal（SIGQUIT, SIG_DFL）; 28: execvp（argv[0], argv）; 29: perror（"cannot execute command"）; 30: exit（1）; 31: } 32: else { 33: if （ wait（&child_info） == -1 ） 34: perror（"wait"）; 35: } 36: return child_info; 37: } 38: