umask

Synopsis

$umask(<mask>)

Technical

Sets EPIC's process-wide file creation mask and returns the previous mask. The first function word is parsed as an integer using base-zero conversion: use a leading zero for octal permission notation, for example 077. Bare 77 is decimal, not octal. Additional words are ignored.

The mask specifies permission bits to remove from newly created files and directories. With ordinary Unix mode handling, the resulting mode is requested_mode & ~mask, not arithmetic subtraction. The system uses only the low nine permission bits (0777). Default ACLs can alter creation behavior; see the system umask interface.

Practical

Use this function to control permissions for future file creation by EPIC and newly launched child processes. It does not change existing file permissions or affect chmod's explicit permission changes. It is not limited to EPIC's built-in file functions.

For example, 077 normally reduces a requested directory mode of 0777 to 0700, and a requested regular-file mode of 0666 to 0600. It cannot add execute bits absent from the requested mode.

Returns and restrictions

The previous mask as a decimal integer, not an octal string. For example, previous mask 077 is returned as 63. Preserve that return value if you intend to restore the mask later.

Missing input returns empty without changing the mask; there is no query-only form. Nonnumeric input becomes zero and therefore clears the mask. Numeric prefixes are accepted, and parsing overflow or narrowing to C int is not reported. Use a valid permission mask. There are no options, settings, or server requirements.

Examples

$umask(077)    Set the creation mask to octal 077; return the previous mask in decimal.
$umask(002)    Normally allow directory mode 0775 and file mode 0664 when requested as 0777/0666.
$umask()       Return empty without changing the mask.

These expressions change the process mask when evaluated; their returned value is not the resulting file mode.

Source

Handler: source/functions.c. Argument and return conversion: include/functions.h.