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PROLOG
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.
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 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:
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 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.
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.
The following sections are informative.
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; 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.
FUTURE DIRECTIONS
None.
SEE ALSO
Section 2.5, Parameters and Variables, basename
The Base Definitions volume of POSIX.1‐2008, Section 3.267, Pathname, Chapter 8, Environment Variables
COPYRIGHT
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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https://www.kernel.org/doc/man-pages/reporting_bugs.html .