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envz_add(3) Library Functions Manual envz_add(3)


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


Standard C library (libc, -lc)


#include <envz.h>
error_t envz_add(char **restrict envz, size_t *restrict envz_len,
               const char *restrict name, const char *restrict value);
char *envz_entry(const char *restrict envz, size_t envz_len,
               const char *restrict name);
char *envz_get(const char *restrict envz, size_t envz_len,
               const char *restrict name);
error_t envz_merge(char **restrict envz, size_t *restrict envz_len,
               const char *restrict envz2, size_t envz2_len,
               int override);
void envz_remove(char **restrict envz, size_t *restrict envz_len,
               const char *restrict name);
void envz_strip(char **restrict envz, size_t *restrict 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 (envzenvz_len) and returns the entry if found, or NULL if not.

envz_get() looks for name in the envz vector (envzenvz_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 (an integer type), and return 0 for success, and ENOMEM if an allocation error occurs.


For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value
envz_add (), envz_entry (), envz_get (), envz_merge (), envz_remove (), envz_strip () Thread safety MT-Safe


These functions are a GNU extension.


#include <envz.h>
#include <stdio.h>
#include <stdlib.h>
main(int argc, char *argv[], char *envp[])

char *str;
size_t e_len = 0;
for (size_t 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);



2023-02-05 Linux man-pages 6.03