expr.c

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/*
 * The expr and test commands.
 *
 * Copyright (C) 1989 by Kenneth Almquist.  All rights reserved.
 * This file is part of ash, which is distributed under the terms specified
 * by the Ash General Public License.  See the file named LICENSE.
 */


#define main exprcmd

#include "bltin.h"
#include "operators.h"
#include <sys/types.h>
#include <sys/stat.h>

#ifndef S_ISLNK
#define lstat           stat
#define S_ISLNK(mode)   (0)
#endif

#define STACKSIZE 12
#define NESTINCR 16

/* data types */
#define STRING 0
#define INTEGER 1
#define BOOLEAN 2


/*
 * This structure hold a value.  The type keyword specifies the type of
 * the value, and the union u holds the value.  The value of a boolean
 * is stored in u.num (1 = TRUE, 0 = FALSE).
 */

struct value {
      int type;
      union {
            char *string;
            long num;
      } u;
};


struct operator {
      short op;                 /* which operator */
      short pri;                /* priority of operator */
};


struct filestat {
      int op;                   /* OP_FILE or OP_LFILE */
      char *name;               /* name of file */
      int rcode;                /* return code from stat */
      struct stat stat;         /* status info on file */
};


extern char *match_begin[10];   /* matched string */
extern short match_length[10];  /* defined in regexp.c */
extern short number_parens;     /* number of \( \) pairs */


#ifdef __STDC__
int expr_is_false(struct value *);
void expr_operator(int, struct value *, struct filestat *);
int lookup_op(char *, char *const*);
char *re_compile(char *);       /* defined in regexp.c */
int re_match(char *, char *);   /* defined in regexp.c */
long atol(const char *);
#else
int expr_is_false();
void expr_operator();
int lookup_op();
char *re_compile();     /* defined in regexp.c */
int re_match(); /* defined in regexp.c */
long atol();
#endif



main(argc, argv)  char **argv; {
      char **ap;
      char *opname;
      char c;
      char *p;
      int print;
      int nest;         /* parenthises nesting */
      int op;
      int pri;
      int skipping;
      int binary;
      struct operator opstack[STACKSIZE];
      struct operator *opsp;
      struct value valstack[STACKSIZE + 1];
      struct value *valsp;
      struct filestat fs;

      INITARGS(argv);
      c = **argv;
      print = 1;
      if (c == 't')
            print = 0;
      else if (c == '[') {
            if (! equal(argv[argc - 1], "]"))
                  error("missing ]");
            argv[argc - 1] = NULL;
            print = 0;
      }
      ap = argv + 1;
      fs.name = NULL;

      /*
       * We use operator precedence parsing, evaluating the expression
       * as we parse it.  Parentheses are handled by bumping up the
       * priority of operators using the variable "nest."  We use the
       * variable "skipping" to turn off evaluation temporarily for the
       * short circuit boolean operators.  (It is important do the short
       * circuit evaluation because under NFS a stat operation can take
       * infinitely long.)
       */

      nest = 0;
      skipping = 0;
      opsp = opstack + STACKSIZE;
      valsp = valstack;
      if (*ap == NULL) {
            valstack[0].type = BOOLEAN;
            valstack[0].u.num = 0;
            goto done;
      }
      for (;;) {
            opname = *ap++;
            if (opname == NULL)
syntax:           error("syntax error");
            if (opname[0] == '(' && opname[1] == '\0') {
                  nest += NESTINCR;
                  continue;
            } else if (*ap && (op = lookup_op(opname, unary_op)) >= 0) {
                  if (opsp == &opstack[0])
overflow:               error("Expression too complex");
                  --opsp;
                  opsp->op = op;
                  opsp->pri = op_priority[op] + nest;
                  continue;

            } else {
                  valsp->type = STRING;
                  valsp->u.string = opname;
                  valsp++;
            }
            for (;;) {
                  opname = *ap++;
                  if (opname == NULL) {
                        if (nest != 0)
                              goto syntax;
                        pri = 0;
                        break;
                  }
                  if (opname[0] != ')' || opname[1] != '\0') {
                        if ((op = lookup_op(opname, binary_op)) < 0)
                              goto syntax;
                        op += FIRST_BINARY_OP;
                        pri = op_priority[op] + nest;
                        break;
                  }
                  if ((nest -= NESTINCR) < 0)
                        goto syntax;
            }
            while (opsp < &opstack[STACKSIZE] && opsp->pri >= pri) {
                  binary = opsp->op;
                  for (;;) {
                        valsp--;
                        c = op_argflag[opsp->op];
                        if (c == OP_INT) {
                              if (valsp->type == STRING)
                                    valsp->u.num = atol(valsp->u.string);
                              valsp->type = INTEGER;
                        } else if (c >= OP_STRING) { /* OP_STRING or OP_FILE */
                              if (valsp->type == INTEGER) {
                                    p = stalloc(32);
#ifdef SHELL
                                    fmtstr(p, 32, "%d", valsp->u.num);
#else
                                    sprintf(p, "%d", valsp->u.num);
#endif
                                    valsp->u.string = p;
                              } else if (valsp->type == BOOLEAN) {
                                    if (valsp->u.num)
                                          valsp->u.string = "true";
                                    else
                                          valsp->u.string = "";
                              }
                              valsp->type = STRING;
                              if (c >= OP_FILE
                               && (fs.op != c
                                   || fs.name == NULL
                                   || ! equal(fs.name, valsp->u.string))) {
                                    fs.op = c;
                                    fs.name = valsp->u.string;
                                    if (c == OP_FILE) {
                                        fs.rcode = stat(valsp->u.string,
                                                                &fs.stat);
                                    } else {
                                        fs.rcode = lstat(valsp->u.string,
                                                                &fs.stat);
                                    }
                              }
                        }
                        if (binary < FIRST_BINARY_OP)
                              break;
                        binary = 0;
                  }
                  if (! skipping)
                        expr_operator(opsp->op, valsp, &fs);
                  else if (opsp->op == AND1 || opsp->op == OR1)
                        skipping--;
                  valsp++;              /* push value */
                  opsp++;               /* pop operator */
            }
            if (opname == NULL)
                  break;
            if (opsp == &opstack[0])
                  goto overflow;
            if (op == AND1 || op == AND2) {
                  op = AND1;
                  if (skipping || expr_is_false(valsp - 1))
                        skipping++;
            }
            if (op == OR1 || op == OR2) {
                  op = OR1;
                  if (skipping || ! expr_is_false(valsp - 1))
                        skipping++;
            }
            opsp--;
            opsp->op = op;
            opsp->pri = pri;
      }
done:
      if (print) {
            if (valstack[0].type == STRING)
                  printf("%s\n", valstack[0].u.string);
            else if (valstack[0].type == INTEGER)
                  printf("%ld\n", valstack[0].u.num);
            else if (valstack[0].u.num != 0)
                  printf("true\n");
      }
      return expr_is_false(&valstack[0]);
}


int
expr_is_false(val)
      struct value *val;
      {
      if (val->type == STRING) {
            if (val->u.string[0] == '\0')
                  return 1;
      } else {  /* INTEGER or BOOLEAN */
            if (val->u.num == 0)
                  return 1;
      }
      return 0;
}


/*
 * Execute an operator.  Op is the operator.  Sp is the stack pointer;
 * sp[0] refers to the first operand, sp[1] refers to the second operand
 * (if any), and the result is placed in sp[0].  The operands are converted
 * to the type expected by the operator before expr_operator is called.
 * Fs is a pointer to a structure which holds the value of the last call
 * to stat, to avoid repeated stat calls on the same file.
 */

void
expr_operator(op, sp, fs)
      int op;
      struct value *sp;
      struct filestat *fs;
      {
      int i;
      struct stat st1, st2;

      switch (op) {
      case NOT:
            sp->u.num = expr_is_false(sp);
            sp->type = BOOLEAN;
            break;
      case ISREAD:
            i = 04;
            goto permission;
      case ISWRITE:
            i = 02;
            goto permission;
      case ISEXEC:
            i = 01;
permission:
            if (fs->stat.st_uid == geteuid())
                  i <<= 6;
            else if (fs->stat.st_gid == getegid())
                  i <<= 3;
            goto filebit;       /* true if (stat.st_mode & i) != 0 */
      case ISFILE:
            i = S_IFREG;
            goto filetype;
      case ISDIR:
            i = S_IFDIR;
            goto filetype;
      case ISCHAR:
            i = S_IFCHR;
            goto filetype;
      case ISBLOCK:
            i = S_IFBLK;
            goto filetype;
      case ISFIFO:
#ifdef S_IFIFO
            i = S_IFIFO;
            goto filetype;
#else
            goto false;
#endif
filetype:
            if ((fs->stat.st_mode & S_IFMT) == i && fs->rcode >= 0) {
true:
                  sp->u.num = 1;
            } else {
false:
                  sp->u.num = 0;
            }
            sp->type = BOOLEAN;
            break;
      case ISSETUID:
            i = S_ISUID;
            goto filebit;
      case ISSETGID:
            i = S_ISGID;
            goto filebit;
      case ISSTICKY:
            i = S_ISVTX;
filebit:
            if (fs->stat.st_mode & i && fs->rcode >= 0)
                  goto true;
            goto false;
      case ISSIZE:
            sp->u.num = fs->rcode >= 0? fs->stat.st_size : 0L;
            sp->type = INTEGER;
            break;
      case ISLINK1:
      case ISLINK2:
            if (S_ISLNK(fs->stat.st_mode) && fs->rcode >= 0)
                  goto true;
            fs->op = OP_FILE;   /* not a symlink, so expect a -d or so next */
            goto false;
      case NEWER:
            if (stat(sp->u.string, &st1) != 0) {
                  sp->u.num = 0;
            } else if (stat((sp + 1)->u.string, &st2) != 0) {
                  sp->u.num = 1;
            } else {
                  sp->u.num = st1.st_mtime >= st2.st_mtime;
            }
            sp->type = INTEGER;
            break;
      case ISTTY:
            sp->u.num = isatty(sp->u.num);
            sp->type = BOOLEAN;
            break;
      case NULSTR:
            if (sp->u.string[0] == '\0')
                  goto true;
            goto false;
      case STRLEN:
            sp->u.num = strlen(sp->u.string);
            sp->type = INTEGER;
            break;
      case OR1:
      case AND1:
            /*
             * These operators are mostly handled by the parser.  If we
             * get here it means that both operands were evaluated, so
             * the value is the value of the second operand.
             */
            *sp = *(sp + 1);
            break;
      case STREQ:
      case STRNE:
            i = 0;
            if (equal(sp->u.string, (sp + 1)->u.string))
                  i++;
            if (op == STRNE)
                  i = 1 - i;
            sp->u.num = i;
            sp->type = BOOLEAN;
            break;
      case EQ:
            if (sp->u.num == (sp + 1)->u.num)
                  goto true;
            goto false;
      case NE:
            if (sp->u.num != (sp + 1)->u.num)
                  goto true;
            goto false;
      case GT:
            if (sp->u.num > (sp + 1)->u.num)
                  goto true;
            goto false;
      case LT:
            if (sp->u.num < (sp + 1)->u.num)
                  goto true;
            goto false;
      case LE:
            if (sp->u.num <= (sp + 1)->u.num)
                  goto true;
            goto false;
      case GE:
            if (sp->u.num >= (sp + 1)->u.num)
                  goto true;
            goto false;
      case PLUS:
            sp->u.num += (sp + 1)->u.num;
            break;
      case MINUS:
            sp->u.num -= (sp + 1)->u.num;
            break;
      case TIMES:
            sp->u.num *= (sp + 1)->u.num;
            break;
      case DIVIDE:
            if ((sp + 1)->u.num == 0)
                  error("Division by zero");
            sp->u.num /= (sp + 1)->u.num;
            break;
      case REM:
            if ((sp + 1)->u.num == 0)
                  error("Division by zero");
            sp->u.num %= (sp + 1)->u.num;
            break;
      case MATCHPAT:
            {
                  char *pat;

                  pat = re_compile((sp + 1)->u.string);
                  if (re_match(pat, sp->u.string)) {
                        if (number_parens > 0) {
                              sp->u.string = match_begin[1];
                              sp->u.string[match_length[1]] = '\0';
                        } else {
                              sp->u.num = match_length[0];
                              sp->type = INTEGER;
                        }
                  } else {
                        if (number_parens > 0) {
                              sp->u.string[0] = '\0';
                        } else {
                              sp->u.num = 0;
                              sp->type = INTEGER;
                        }
                  }
            }
            break;
      }
}


int
lookup_op(name, table)
      char *name;
      char *const*table;
      {
      register char *const*tp;
      register char const *p;
      char c = name[1];

      for (tp = table ; (p = *tp) != NULL ; tp++) {
            if (p[1] == c && equal(p, name))
                  return tp - table;
      }
      return -1;
}

---