getusershell, setusershell, endusershell - get permitted user shells
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
Since glibc 2.21:
In glibc 2.19 and 2.20:
_DEFAULT_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)
Up to and including glibc 2.19:
_BSD_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)
The getusershell() function returns the next line from the file /etc/shells, opening the file if necessary. The line should contain the pathname of a valid user shell. If /etc/shells does not exist or is unreadable, getusershell() behaves as if /bin/sh and /bin/csh were listed in the file.
The setusershell() function rewinds /etc/shells.
The endusershell() function closes /etc/shells.
The getusershell() function returns NULL on end-of-file.
For an explanation of the terms used in this section, see attributes(7).
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