NAME
getmode
, setmode
— modify mode bits
LIBRARY
library “libc”
SYNOPSIS
#include
<unistd.h>
void *
setmode
(const
char *mode_str);
mode_t
getmode
(const
void *set, mode_t
mode);
DESCRIPTION
Thesetmode
()
function accepts a string representation of a file mode change, compiles it to
binary form, and returns an abstract representation 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 represent 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 duplicated 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 specified for the library
routines malloc(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
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 *.