/* $Id: envvar.c,v 1.3 2002/03/02 21:02:21 sverrehu Exp $ */ /************************************************************************** * * FILE envvar.c * * DESCRIPTION Routines to expand environment-variables into strings. * Will understand both $ENV and ${ENV} -type variables. * * WRITTEN BY Sverre H. Huseby * * CREATED 1995-10-03 * **************************************************************************/ #include #include #include #include "envvar.h" #ifndef NULL #define NULL 0 #endif /************************************************************************** * * * P R I V A T E F U N C T I O N S * * * **************************************************************************/ /*------------------------------------------------------------------------- * * NAME strDel * * FUNCTION Delete characters from a string. * * INPUT s the string to delete characters from. * idx index of first character to delete. * n number of characters to delete. * * OUTPUT s string with characters deleted. * * DESCRIPTION Deletes characters from a string by moving following * characters back. * */ static void strDel(char *s, int idx, int n) { int l; char *p; if (idx >= (l = strlen(s))) return; if (idx + n > l) n = l - idx; s += idx; p = s + n; do { *s++ = *p; } while (*p++); } /*------------------------------------------------------------------------- * * NAME strIns * * FUNCTION Insert a string into a string. * * INPUT s the string to insert into. * ins the string to insert. * idx index of where to insert the string. * max max length of s, including '\0'. * * OUTPUT s string with characters inserted. * * DESCRIPTION The insertion will be done even if the string gets to * long, but characters will be sacrificed at the end of s. * The string is always '\0'-terminated. * */ static void strIns(char *s, const char *ins, int idx, int max) { int l, li, move; char *p1, *p2; if (idx > (l = strlen(s))) idx = l; li = strlen(ins); move = l - idx + 2; /* include '\0' in move */ p1 = s + l; p2 = p1 + li; while (p2 >= s + max) { --p1; --p2; --move; } while (move-- > 0) *p2-- = *p1--; p1 = s + idx; if (idx + li >= max) li = max - idx - 1; while (li--) *p1++ = *ins++; s[max - 1] = '\0'; } /*------------------------------------------------------------------------- * * NAME findEnvVar * * FUNCTION Find first environment variable in a string. * * INPUT s the string to scan. * * OUTPUT len length of variable, including $ and { }. * * RETURNS Pointer to the $ that introduces the variable, or NULL * if no variable is found. * * DESCRIPTION Searches for matches like $NAME and ${NAME}, where NAME is * a sequence of characters, digits and underscores, of which * the first can not be a digit. * * NOTE This function will only return `legal' variables. There * may be $'s in the string that are not followed by what * is considered a legal variable name introducer. Such * occurrences are skipped. * */ static char * findEnvVar(const char *s, int *len) { int brace = 0; char *ret = NULL; const char *next; if (!s) return NULL; while (*s) { next = s + 1; if (*s == '$' && (isalpha(*next) || *next == '_' || *next == '{')) { ret = (char *) s++; if (*s == '{') { brace = 1; ++s; } while (*s && (isalnum(*s) || *s == '_')) ++s; *len = s - ret; if (brace) { if (*s == '}') { ++*len; break; } ret = NULL; } else break; } ++s; } return ret; } /*------------------------------------------------------------------------- * * NAME getEnv * * FUNCTION Look up environment variable. * * INPUT name name of environment variable to look up. This * may include $ and { }. * * RETURNS The variable contents, or "" if not found. * */ static const char * getEnv(const char *name) { static char *empty = ""; char *ret, *tmp, *p, *p2; if ((tmp = strdup(name)) == NULL) return empty; /* better than no test at all. */ p = tmp; if (*p == '$') ++p; if (*p == '{') { ++p; if ((p2 = strchr(p, '}')) != NULL) *p2 = '\0'; } if ((ret = getenv(p)) == NULL) ret = empty; free(tmp); return ret; } /************************************************************************** * * * P U B L I C F U N C T I O N S * * * **************************************************************************/ /*------------------------------------------------------------------------- * * NAME envExpand * * FUNCTION Expand environment variables in a string. * * SYNOPSIS #include "envvar.h" * int envExpand(char *s, int max); * * INPUT s string to expand environment variables in. * max max length of string, including '\0'. * * OUTPUT s the string with environment variables expanded. * * RETURNS Number of changes done. * * NOTES A non-existing variable is substituted with the empty * string. * */ int envExpand(char *s, int max) { char *var, *s2, save; const char *env; int len, ret = 0; s2 = s; while ((var = findEnvVar(s2, &len)) != NULL) { ++ret; save = var[len]; var[len] = '\0'; env = getEnv(var); var[len] = save; strDel(s, var - s, len); strIns(s, env, var - s, max); s2 = var + strlen(env); } return ret; } /*------------------------------------------------------------------------- * * NAME envDupExpand * * FUNCTION Expand environment variables into a new string. * * SYNOPSIS #include "envvar.h" * char *envDupExpand(const char *s, int extra); * * INPUT s string to expand environment variables in. * extra number of extra bytes to allocate in the * string, in addition to the string contents * and the terminating '\0'. * * RETURNS A dynamically allocated string with environment * variables expanded. * Use free() to deallocate the buffer when it is no * longer needed. * NULL is returned if there is not enough memory. * * NOTES A non-existing variable is substituted with the empty * string. * */ char * envDupExpand(const char *s, int extra) { char *var, *ret, save; const char *env, *s2; int len, slen, elen, bufflen; /* * calculate length needed. */ s2 = s; slen = strlen(s); bufflen = slen + 1 + extra; while ((var = findEnvVar(s2, &len)) != NULL) { save = var[len]; var[len] = '\0'; env = getEnv(var); var[len] = save; elen = strlen(env); /* need to make a buffer the maximum possible size, else we * may get trouble while expanding. */ bufflen += len > elen ? len : elen; s2 = var + len; } if (bufflen < slen + 1) bufflen = slen + 1; if ((ret = malloc(bufflen)) == NULL) return ret; /* * now do the real expansion. */ strcpy(ret, s); envExpand(ret, bufflen - extra); return ret; }