DIRNAME(P) POSIX Programmer's Manual DIRNAME(P)
dirname - return the directory portion of a pathname
The string operand shall be treated as a pathname, as defined in the Base Definitions vol-
ume of IEEE Std 1003.1-2001, Section 3.266, 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.
The following operand shall be supported:
string A string.
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 IEEE Std 1003.1-2001, Section 8.2, Inter-
nationalization 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 interna-
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 argu-
Determine the locale that should be used to affect the format and contents of diag-
nostic messages written to standard error.
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 Successful completion.
>0 An error occurred.
CONSEQUENCES OF ERRORS
The following sections are informative.
The definition of pathname specifies implementation-defined behavior for pathnames start-
ing with two slash characters. Therefore, applications shall not arbitrarily add slashes
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 / /
dirname // / or //
dirname /a/b/ /a
dirname //a//b// //a
dirname a . ($? = 0)
dirname "" . ($? = 0)
dirname /a /
dirname /a/b /a
dirname a/b a
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 IEEE Std 1003.1-2001 have been
coordinated so that when string is a valid pathname:
would be a valid filename for the file in the directory:
This would not work for the versions of these utilities in early proposals due to the way
processing of trailing slashes was specified. Consideration was given to leaving process-
ing unspecified if there were trailing slashes, but this cannot be done; the Base Defini-
tions volume of IEEE Std 1003.1-2001, Section 3.266, Pathname allows trailing slashes. The
basename and dirname utilities have to specify consistent handling for all valid path-
basename() , Parameters and Variables
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by
the Institute of Electrical and Electronics Engineers, Inc and The Open Group. 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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 DIRNAME(P)