SETMODE(3)

SETMODE(3) | 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 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

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 *.

January 4, 2009 | NetBSD 9.5