IEEE/The Open Group
This manual page is part of the POSIX Programmer’s Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
dirname — return the directory portion of a pathname
The string operand shall be treated as a pathname, as defined in the Base Definitions volume of POSIX.1-2008, Section 3.267, 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:
The resulting string shall be written to standard output.
|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 following operand shall be supported:
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 the Base Definitions volume of POSIX.1-2008, Section 8.2, 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||Determine the location of message catalogs for the processing of LC_MESSAGES.|
The dirname utility shall write a line to the standard output in the following format:
"%s\n", <resulting string>
The standard error shall be used only for diagnostic messages.
The following exit values shall be returned:
|>0||An error occurred.|
CONSEQUENCES OF ERRORS
The following sections are informative.
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.
|dirname //||/ or //|
|dirname a||. ($? = 0)|
|dirname ""||. ($? = 0)|
See also the examples for the basename utility.
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; the Base Definitions volume of POSIX.1-2008, Section 3.267, Pathname allows trailing <slash> characters. The basename and dirname utilities have to specify consistent handling for all valid pathnames.
Section 2.5, Parameters and Variables, basename
The Base Definitions volume of POSIX.1-2008, Section 3.267, Pathname, Chapter 8, Environment Variables
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html .
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