---
name: "setmode"
section: "3"
platform: "linux"
package: "libbsd-dev"
version: "0.8.3-1"
release: "Debian 9 (Stretch)"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/setmode"
---

# setmode(3)

modify mode bits

## NAME

**getmode**, **setmode** – modify mode bits

## LIBRARY

library “libbsd”

## SYNOPSIS

**#include \<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)](/chmod/1.md), 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)](/umask/2.md), 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, 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)](/malloc/3.md) or [strtol(3)](/strtol/3.md). In addition, **setmode**() will fail and set *errno* to:

- \[EINVAL\]

  The *mode* argument does not represent a valid mode.

## SEE ALSO

[chmod(1)](/chmod/1.md), [stat(2)](/stat/2.md), [umask(2)](/umask/2.md), [malloc(3)](/malloc/3.md)

## HISTORY

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

## BUGS

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