Section (3) envz_add

Linux manual pages Section 3  


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


#include <envz.h>
error_t 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);
error_t envz_merge( char **envz,
  size_t *envz_len,
  const char *envz2,
  size_t envz2_len,
  int override);
void envz_remove( char **envz,
  size_t *envz_len,
  const char *name);
void 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 _zsingle_quotesz_=_zsingle_quotesz_ is considered to be the value. If there is no _zsingle_quotesz_=_zsingle_quotesz_, the value is taken to be NULL. (While the value in case of a trailing _zsingle_quotesz_=_zsingle_quotesz_ 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 _zsingle_quotesz_=_zsingle_quotesz_ 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.


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. Handle with care.


#include <stdio.h>
#include <stdlib.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);
, str);
    str = envz_get(*envp, e_len, HOME);
, str);




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  Copyright 2002 walter harms (

Distributed under GPL

based on the description in glibc source and infopages

Corrections and additions, aeb