CS 25200: Systems Programming. Lecture 16: Wildcards

Transcription

1 CS 25200: Systems Programming Lecture 16: Wildcards Dr. Jef Turkstra 2018 Dr. Jeffrey A. Turkstra 1

2 Announcements Updated test cases available 2018 Dr. Jeffrey A. Turkstra 2

3 Lecture 16 Executor review Termination Wildcards 2018 Dr. Jeffrey A. Turkstra 3

4 Executor Parent process sets up all piping and redirection before forking children Children inherit redirections Parent must save original fds and restore them stderr should be the same for all processes $ A b c d > out < in 2018 Dr. Jeffrey A. Turkstra 4

5 execute() { //save in/out int tmpin = dup(0); int tmpout = dup(1); //set the initial input int fdin; if (infile) { fdin = open(infile,...); else { // Use default input fdin = dup(tmpin); int ret; int fdout; for (i = 0; i < numsimplecommands; i++) { //redirect input dup2(fdin, 0); close(fdin); //setup output if (i == numsimplecommands - 1){ // Last simple command if (outfile){ fdout = open(outfile,...); else { // Use default output fdout = dup(tmpout); 2018 Dr. Jeffrey A. Turkstra 5

6 else { // Not last simple command //create pipe int fdpipe[2]; pipe(fdpipe); fdout = fdpipe[1]; fdin = fdpipe[0]; // if/else // Redirect output dup2(fdout,1); close(fdout); // Create child process ret = fork(); if (ret == 0) { execvp(scmd[i].args[0], scmd[i].args); perror( execvp ); exit(1); // for //restore in/out defaults dup2(tmpin,0); dup2(tmpout,1); close(tmpin); close(tmpout); if (!background) { // Wait for last command waitpid(ret, NULL,0 ); // execute 2018 Dr. Jeffrey A. Turkstra 6

7 exit() and _exit() void exit(int status) cause normal process termination All atexit() and on_exit() registered functions are exectued In reverse order stdio streams are fushed and closed tmpfle() fles are removed void _exit(int status) terminate the process immediately fds still closed 2018 Dr. Jeffrey A. Turkstra 7

8 Shell strategy notes Remember, fdin tracks the input for the next command Will either be the input fle fd (for the frst command) or fdpipe[0] Example only handles pipes and input/output redirection Have to handle stderr redirection Applies to all processes Also have to handle the append cases 2018 Dr. Jeffrey A. Turkstra 8

9 Shell Final Command Table ls -al aab aaa grep me In:dft Out:flee Err:dft Lexer Parser shell.l shell.y wildcards env vars executor ls -al a* grep me > flee <ls> <-al> <a*> <PIPE> <grep> <me> <GREAT> <flee> Command Table ls -al a* grep me In:dft Out:flee Err:dft 2018 Dr. Jeffrey A. Turkstra 9

10 Wildcards Allow us to perform actions on more than one fle at a time Also called fle globbing Do not confuse with regular expressions 2018 Dr. Jeffrey A. Turkstra 10

11 Standard wildcards $ man 7 glob?: any single character DSCN00??.JPG *: any number of characters, including zero a*a *.c t*.log [ ]: a range m[a-d]m m[0-7]n { : or relationship no spaces allowed cp {*.doc,*.pdf ~ [!]: anything not in the range \: escape character 2018 Dr. Jeffrey A. Turkstra 11

12 Our shell Only need to worry about * and? Implement the simple case frst Add a function to shell.y to do the expansion 2018 Dr. Jeffrey A. Turkstra 12

13 shell.y Before argument: WORD { Command::_currentSimpleCommand->insertArgument($1); ; After argument: WORD { expandwildcardsifnecessary($1); ; 2018 Dr. Jeffrey A. Turkstra 13

14 POSIX Regular expressions int regcomp(regex_t *preg, const char *regex, int cfags) Compiles the regular expression into a form that regexec() can use Completes the passed regex_t Finite state automata int regexec(const regex_t *preg, const char *string, size_t nmatch, regmatch_t pmatch[], int efags) Do the actual comparison typedef struct { regoff_t rm_so; regoff_t rm_eo; regmatch_t; 2018 Dr. Jeffrey A. Turkstra 14

15 void regfree(regex_t *preg) regex_t s contain dynamically allocated memory You have to free it or you ll have a memory leak Even have to free before reusing! Does not free the regex_t itself 2018 Dr. Jeffrey A. Turkstra 15

16 Implementation Simple case void expandwildcardsifnecessary(char *arg) { // return if arg does not contain wildcard(s) if (arg has neither * or? ) { // strchr() might help Command::_currentSimpleCommand>insertArguments(arg); return; 2018 Dr. Jeffrey A. Turkstra 16

17 Implementation // 1. Convert wildcard to regular expression // Convert * ->.* //? ->. //. -> \. and others you need // Also add ^ at the beginning and $ at the end to match // the beginning ant the end of the word. // Allocate enough space for regular expression char *reg = (char*) malloc(2*strlen(arg)+10); char *a = arg; char *r = reg; *r = ^ ; r++; // match beginning of line while (*a) { if (*a == * ) { *r=. ; r++; *r= * ; r++; else if (*a ==? ) { *r=. ; r++; else if (*a ==. ) { *r= \\ ; r++; *r=. ; r++; else { *r=*a; r++; a++; *r= $ ; r++; *r=0;// match end of line and add null char 2018 Dr. Jeffrey A. Turkstra 17

18 Implementation // 2. compile regular expression. See lab3-src/regular.cc char *expbuf = regcomp(reg,... ); if (expbuf == NULL) { perror( compile ); return; // 3. List directory and add as arguments the entries // that match the regular expression DIR *dir = opendir(. ); if (dir == NULL) { perror( opendir ); return; 2018 Dr. Jeffrey A. Turkstra 18

19 Implementation struct dirent * ent; while ((ent = readdir(dir))!= NULL) { // Check if name matches if (regexec(ent->d_name, expbuf) ==0 ) { // Add argument Command::_currentSimpleCommand insertargument(strdup(ent d_name)); closedir(dir); 2018 Dr. Jeffrey A. Turkstra 19

20 Note! Previous code is incomplete and contains errors Only intended as a starting point 2018 Dr. Jeffrey A. Turkstra 20

21 Sorting Entries generated from a wildcard are presented in sorted order by most shells E.g., $ echo * Your shell should too 2018 Dr. Jeffrey A. Turkstra 21

22 Sorting struct dirent * ent; int maxentries = 20; int nentries = 0; char **array = (char**) malloc(maxentries*sizeof(char*)); while ((ent = readdir(dir))!= NULL) { // Check if name matches if (regexec(ent->d_name, expbuf)) { if (nentries == maxentries) { maxentries *= 2; array = realloc(array, maxentries*sizeof(char*)); assert(array!=null); array[nentries]= strdup(ent->d_name); nentries++; closedir(dir); sortarraystrings(array, nentries); // Add arguments for (int i = 0; i < nentries; i++) { Command::_currentSimpleCommand->insertArgument( strdup(ent->insertargument(array[i])); free(array); // What s wrong here? 2018 Dr. Jeffrey A. Turkstra 22

23 Dot fles Sometimes called hidden fles.,..,.login,.bashrc, etc Not included in directory listings Unless -a Not matched by wildcards Unless frst character of pattern is Dr. Jeffrey A. Turkstra 23

24 if (regexec (...) ) { if (ent->d_name[0] ==. ) { if (arg[0] ==. ) add filename to arguments; else { add ent->d_name to arguments 2018 Dr. Jeffrey A. Turkstra 24

25 Subdirectory wildcards Wildcards match directories in a pattern as well E.g. echo /e*/a*/b*/*.conf 2018 Dr. Jeffrey A. Turkstra 25

26 Rabbit holes /usr/lib/a* /usr/lib/aa /usr/lib/abb /usr/l*/a* /usr/local/a* /usr/local/axz /usr/local/a12 /u*/l*/a* /u/l*/a* /u/loc/a* /u/loc/aq /u/loc/ar /u/lll/a* /u/lll/apple /u/lll/atp /unix/l*/a* /unix/134/a* /unix/134/abcd /unix/134/a45 /unix/lll/a* /unix/lll/ab /unix/lll/ap Dr. Jeffrey A. Turkstra 26

27 Questions? 2018 Dr. Jeffrey A. Turkstra 27