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NAME |LIBRARY |SYNOPSIS |DESCRIPTION |RETURN VALUE |ATTRIBUTES |STANDARDS |HISTORY |NOTES |SEE ALSO |COLOPHON | |
getenv(3) Library Functions Manualgetenv(3)getenv, secure_getenv - get an environment variable
Standard C library (libc,-lc)
#include <stdlib.h>char *getenv(const char *name);char *secure_getenv(const char *name); Feature Test Macro Requirements for glibc (seefeature_test_macros(7)):secure_getenv(): _GNU_SOURCE
Thegetenv() function searches the environment list to find the environment variablename, and returns a pointer to the correspondingvalue string. The GNU-specificsecure_getenv() function is just likegetenv() except that it returns NULL in cases where "secure execution" is required. Secure execution is required if one of the following conditions was true when the program run by the calling process was loaded: • the process's effective user ID did not match its real user ID or the process's effective group ID did not match its real group ID (typically this is the result of executing a set-user- ID or set-group-ID program); • the effective capability bit was set on the executable file; or • the process has a nonempty permitted capability set. Secure execution may also be required if triggered by some Linux security modules. Thesecure_getenv() function is intended for use in general- purpose libraries to avoid vulnerabilities that could occur if set-user-ID or set-group-ID programs accidentally trusted the environment.
Thegetenv() function returns a pointer to the value in the environment, or NULL if there is no match.
For an explanation of the terms used in this section, seeattributes(7). ┌──────────────────────────────────┬───────────────┬─────────────┐ │Interface│Attribute│Value│ ├──────────────────────────────────┼───────────────┼─────────────┤ │getenv(),secure_getenv() │ Thread safety │ MT-Safe env │ └──────────────────────────────────┴───────────────┴─────────────┘
getenv() C11, POSIX.1-2008.secure_getenv() GNU.
getenv() POSIX.1-2001, C89, C99, SVr4, 4.3BSD.secure_getenv() glibc 2.17.
The strings in the environment list are of the formname=value. As typically implemented,getenv() returns a pointer to a string within the environment list. The caller must take care not to modify this string, since that would change the environment of the process. The implementation ofgetenv() is not required to be reentrant. The string pointed to by the return value ofgetenv() may be statically allocated, and can be modified by a subsequent call togetenv(),putenv(3),setenv(3), orunsetenv(3). The "secure execution" mode ofsecure_getenv() is controlled by theAT_SECUREflag contained in the auxiliary vector passed from the kernel to user space.
clearenv(3),getauxval(3),putenv(3),setenv(3),unsetenv(3),capabilities(7),environ(7)
This page is part of theman-pages (Linux kernel and C library user-space interface documentation) project. Information about the project can be found at ⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report for this manual page, see ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩. This page was obtained from the tarball man-pages-6.15.tar.gz fetched from ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on 2025-08-11. If you discover any rendering problems in this HTML version of the page, or you believe there is a better or more up- to-date source for the page, or you have corrections or improvements to the information in this COLOPHON (which isnot part of the original manual page), send a mail to man-pages@man7.orgLinux man-pages 6.15 2025-05-17getenv(3)Pages that refer to this page:clearenv(3), getauxval(3), libsystemd(3), libudev(3), pmgetconfig(3), putenv(3), sd-bus(3), sd_bus_add_match(3), sd_bus_add_node_enumerator(3), sd_bus_add_object(3), sd_bus_add_object_manager(3), sd_bus_attach_event(3), sd_bus_call(3), sd_bus_call_method(3), sd_bus_can_send(3), sd_bus_close(3), sd_bus_creds_get_pid(3), sd_bus_creds_new_from_pid(3), sd_bus_default(3), sd_bus_emit_signal(3), sd_bus_enqueue_for_read(3), sd_bus_error(3), sd_bus_error_add_map(3), sd-bus-errors(3), sd_bus_get_current_handler(3), sd_bus_get_fd(3), sd_bus_get_name_creds(3), sd_bus_get_name_machine_id(3), sd_bus_interface_name_is_valid(3), sd_bus_is_open(3), sd_bus_list_names(3), sd_bus_message_append(3), sd_bus_message_append_array(3), sd_bus_message_append_basic(3), sd_bus_message_append_string_memfd(3), sd_bus_message_append_strv(3), sd_bus_message_at_end(3), sd_bus_message_copy(3), sd_bus_message_dump(3), sd_bus_message_get_cookie(3), sd_bus_message_get_monotonic_usec(3), sd_bus_message_get_signature(3), sd_bus_message_get_type(3), sd_bus_message_new(3), sd_bus_message_new_method_call(3), sd_bus_message_new_method_error(3), sd_bus_message_new_signal(3), sd_bus_message_open_container(3), sd_bus_message_read(3), sd_bus_message_rewind(3), sd_bus_message_seal(3), sd_bus_message_sensitive(3), sd_bus_message_set_destination(3), sd_bus_message_set_expect_reply(3), sd_bus_message_skip(3), sd_bus_message_verify_type(3), sd_bus_negotiate_fds(3), sd_bus_new(3), sd_bus_path_encode(3), sd_bus_pending_method_calls(3), sd_bus_process(3), sd_bus_query_sender_creds(3), sd_bus_reply_method_error(3), sd_bus_reply_method_return(3), sd_bus_request_name(3), sd_bus_send(3), sd_bus_set_address(3), sd_bus_set_close_on_exit(3), sd_bus_set_connected_signal(3), sd_bus_set_description(3), sd_bus_set_exit_on_disconnect(3), sd_bus_set_fd(3), sd_bus_set_method_call_timeout(3), sd_bus_set_property(3), sd_bus_set_sender(3), sd_bus_set_server(3), sd_bus_set_watch_bind(3), sd_bus_slot_get_bus(3), sd_bus_slot_ref(3), sd_bus_slot_set_description(3), sd_bus_slot_set_destroy_callback(3), sd_bus_slot_set_floating(3), sd_bus_slot_set_userdata(3), sd_bus_start(3), sd_bus_track_add_name(3), sd_bus_track_new(3), sd_bus_wait(3), sd-daemon(3), sd-device(3), sd_device_get_syspath(3), sd-event(3), sd_event_add_child(3), sd_event_add_defer(3), sd_event_add_inotify(3), sd_event_add_io(3), sd_event_add_memory_pressure(3), sd_event_add_signal(3), sd_event_add_time(3), sd_event_exit(3), sd_event_get_fd(3), sd_event_new(3), sd_event_now(3), sd_event_run(3), sd_event_set_signal_exit(3), sd_event_set_watchdog(3), sd_event_source_get_event(3), sd_event_source_get_pending(3), sd_event_source_set_description(3), sd_event_source_set_destroy_callback(3), sd_event_source_set_enabled(3), sd_event_source_set_exit_on_failure(3), sd_event_source_set_floating(3), sd_event_source_set_prepare(3), sd_event_source_set_priority(3), sd_event_source_set_ratelimit(3), sd_event_source_set_userdata(3), sd_event_source_unref(3), sd_event_wait(3), sd_get_seats(3), sd-hwdb(3), sd_hwdb_get(3), sd_hwdb_new(3), sd-id128(3), sd_id128_get_machine(3), sd_id128_randomize(3), sd_id128_to_string(3), sd-journal(3), sd_journal_add_match(3), sd_journal_print(3), sd-json(3), sd_listen_fds(3), sd-login(3), sd_login_monitor_new(3), sd_machine_get_class(3), sd_notify(3), sd_path_lookup(3), sd_seat_get_active(3), sd_session_is_active(3), sd_uid_get_state(3), sd-varlink(3), sd_varlink_push_fd(3), sd_varlink_send(3), sd_varlink_set_description(3), sd_watchdog_enabled(3), setenv(3), tzset(3), attributes(7), environ(7)
HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |