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ENVZ_ADD (3) | C library functions | Unix Manual Pages | :man


envz_add, envz_entry, envz_get, envz_merge, envz_remove, envz_strip - environment string support




"#include <envz.h>"


"envz_add(char **"envz", size_t *"envz_len,

"const char *"name", const char *"value);

"char *"

"envz_entry(const char *"envz", size_t *"envz_len", const char *"name);

"char *"

"envz_get(const char *"envz", size_t *"envz_len", const char *"name);


"envz_merge(char **"envz", size_t *"envz_len,

"const char *"envz2", size_t "envz2_len", int "override);


"envz_remove(char **"envz", size_t *"envz_len", const char *"name);


"envz_strip(char **"envz", size_t *"envz_len);


These functions are glibc-specific.

An argz vector is a pointer to a character buffer together with a length, see argz_add(3). An envz vector is a special argz vector, namely one where the strings have the form "name=value". Everything after the first ’=’ is considered to be the value. If there is no ’=’, the value is taken to be NULL. (While the value in case of a trailing ’=’ is the empty string "".)

These functions are for handling envz vectors.

envz_add() adds the string " name = value " (in case value is non-NULL) or " name " (in case value is NULL) to the envz vector (*envz,*envz_len) and updates *envz and *envz_len. If an entry with the same name existed, it is removed.

envz_entry() looks for name in the envz vector (envz,envz_len) and returns the entry if found, or NULL if not.

envz_get() looks for name in the envz vector (envz,envz_len) and returns the value if found, or NULL if not. (Note that the value can also be NULL, namely when there is an entry for name without ’=’ sign.)

envz_merge() adds each entry in envz2 to *envz, as if with envz_add(). If override is true, then values in envz2 will supersede those with the same name in *envz, otherwise not.

envz_remove() removes the entry for name from (*envz,*envz_len) if there was one.

envz_strip removes all entries with value NULL.


All envz functions that do memory allocation have a return type of error_t, and return 0 for success, and ENOMEM if an allocation error occurs.


#include <stdio.h>
#include <envz.h>
main(int argc, char *argv[], char *envp[]) {
int i, e_len = 0;
char *str;

for (i=0; envp[i] != NULL; i++)
e_len += strlen(envp[i]) + 1;

str = envz_entry(*envp, e_len, "HOME");
printf("%s\n", str);
str = envz_get(*envp, e_len, "HOME");
printf("%s\n", str);
return 0;


These functions are a GNU extension. Handle with care.



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