setmode(3) - NetBSD Manual Pages

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SETMODE(3)              NetBSD Library Functions Manual             SETMODE(3)


NAME

     getmode, setmode -- modify mode bits


LIBRARY

     Standard C Library (libc, -lc)


SYNOPSIS

     #include <unistd.h>

     void *
     setmode(const char *mode_str);

     mode_t
     getmode(const void *set, mode_t mode);


DESCRIPTION

     The setmode() function accepts a string representation of a file mode
     change, compiles it to binary form, and returns an abstract representa-
     tion that may be passed to getmode().  The string may be an numeric
     (octal) or symbolic string of the form accepted by chmod(1), and may rep-
     resent either an exact mode to set or a change to make to the existing
     mode.

     The getmode() function adjusts the file permission bits given by mode
     according to the compiled change representation set, and returns the
     adjusted mode.  While only the permission bits are altered, other parts
     of the file mode, particularly the type, may be examined.

     Because some of the possible symbolic values are defined relative to the
     file creation mask, setmode() may call umask(2), temporarily changing the
     mask.  If this occurs, the file creation mask will be restored before
     setmode() returns.  If the calling program changes the value of its file
     creation mask after calling setmode(), setmode() must be called again to
     recompile the mode string if getmode() is to modify future file modes
     correctly.

     If the mode passed to setmode() is invalid, setmode() returns NULL.


EXAMPLES

     The effects of the shell command `chmod a+x myscript.sh' can be dupli-
     cated as follows:

           const char *file = "myscript.sh";
           struct stat st;
           mode_t newmode;

           stat(file, &st);
           newmode = getmode(setmode("a+x"), st.st_mode);
           chmod(file, newmode);


ERRORS

     The setmode() function may fail and set errno for any of the errors spec-
     ified for the library routines reallocarr(3) or strtol(3).  In addition,
     setmode() will fail and set errno to:

     [EINVAL]           The mode argument does not represent a valid mode.


SEE ALSO

     chmod(1), stat(2), umask(2), malloc(3)


HISTORY

     The getmode() and setmode() functions first appeared in 4.4BSD.


BUGS

     Each call to setmode allocates a small amount of memory that there is no
     correct way to free.

     The type of set should really be some opaque struct type used only by
     these functions rather than void *.

NetBSD 10.1                     March 12, 2022                     NetBSD 10.1