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setmode(3)

January 4, 2009
Aliases: getmode(3), getmode(3)

libbsd-dev

utility functions from BSD systems - development files

libbsd-devel

Development files for libbsd

NAME

getmode, setmode - modify mode bits

LIBRARY


.Lb libbsd

SYNOPSIS


.In bsd/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 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.
The value returned from setmode is obtained from malloc and should be returned to the system with free when the program is done with it, generally after a call to getmode.

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, Am]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.

HISTORY

The getmode and setmode functions first appeared in BSD 4.4 .

BUGS

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