NAME

dirname - return the directory portion of a pathname

SYNOPSIS

dirname string

DESCRIPTION

The string operand shall be treated as a pathname, as defined in XBD Pathname. The string string shall be converted to the name of the directory containing the filename corresponding to the last pathname component in string, performing actions equivalent to the following steps in order:

1. If string is //, skip steps 2 to 5.

2. If string consists entirely of <slash> characters, string shall be set to a single <slash> character. In this case, skip steps 3 to 8.

3. If there are any trailing <slash> characters in string, they shall be removed.

4. If there are no <slash> characters remaining in string, string shall be set to a single <period> character. In this case, skip steps 5 to 8.

5. If there are any trailing non- <slash> characters in string, they shall be removed.

6. If the remaining string is //, it is implementation-defined whether steps 7 and 8 are skipped or processed.

7. If there are any trailing <slash> characters in string, they shall be removed.

8. If the remaining string is empty, string shall be set to a single <slash> character.

The resulting string shall be written to standard output.

OPTIONS

None.

OPERANDS

The following operand shall be supported:

string

A string.

STDIN

Not used.

INPUT FILES

None.

ENVIRONMENT VARIABLES

The following environment variables shall affect the execution of dirname:

LANG

Provide a default value for the internationalization variables that are unset or null. (See XBD Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.)

LC_ALL

If set to a non-empty string value, override the values of all the other internationalization variables.

LC_CTYPE

Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multi-byte characters in arguments).

LC_MESSAGES

Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.

NLSPATH

^[XSI] Determine the location of message catalogs for the processing of LC_MESSAGES.

ASYNCHRONOUS EVENTS

Default.

STDOUT

The dirname utility shall write a line to the standard output in the following format:

"%s\n", <resulting string>

STDERR

The standard error shall be used only for diagnostic messages.

OUTPUT FILES

None.

EXTENDED DESCRIPTION

None.

EXIT STATUS

The following exit values shall be returned:

 0

Successful completion.

>0

An error occurred.

CONSEQUENCES OF ERRORS

Default.

APPLICATION USAGE

The definition of pathname specifies implementation-defined behavior for pathnames starting with two <slash> characters. Therefore, applications shall not arbitrarily add <slash> characters to the beginning of a pathname unless they can ensure that there are more or less than two or are prepared to deal with the implementation-defined consequences.

EXAMPLES

Command	Results
dirname /	/
dirname //	/ or //
dirname /a/b/	/a
dirname //a//b//	//a
dirname	Unspecified
dirname a	. ($? = 0)
dirname ""	. ($? = 0)
dirname /a	/
dirname /a/b	/a
dirname a/b	a

See also the examples for the basename utility.

RATIONALE

The dirname utility originated in System III. It has evolved through the System V releases to a version that matches the requirements specified in this description in System V Release 3. 4.3 BSD and earlier versions did not include dirname.

The behaviors of basename and dirname in this volume of POSIX.1-2008 have been coordinated so that when string is a valid pathname:

$(basename -- "string")

would be a valid filename for the file in the directory:

$(dirname -- "string")

This would not work for the versions of these utilities in early proposals due to the way processing of trailing <slash> characters was specified. Consideration was given to leaving processing unspecified if there were trailing <slash> characters, but this cannot be done; XBD Pathname allows trailing <slash> characters. The basename and dirname utilities have to specify consistent handling for all valid pathnames.

FUTURE DIRECTIONS

None.

SEE ALSO

Parameters and Variables, basename

XBD Pathname, Environment Variables

CHANGE HISTORY

First released in Issue 2.

Issue 7

POSIX.1-2008, Technical Corrigendum 1, XCU/TC1-2008/0083 [192,430], XCU/TC1-2008/0084 [192], and XCU/TC1-2008/0085 [192] are applied.