The string operand shall be treated as a pathname, as defined in the Base
Definitions volume of IEEE Std 1003.1-2001, Section 3.266,
Pathname. The string string shall be converted to the filename
corresponding to the last pathname component in string and then the
suffix string suffix, if present, shall be removed. This shall be done
by performing actions equivalent to the following steps in order:
If string is a null string, it is unspecified
whether the resulting string is '.' or a null string. In either
case, skip steps 2 through 6.
If string is "//" , it is
implementation-defined whether steps 3 to 6 are skipped or processed.
If string consists entirely of slash characters,
string shall be set to a single slash character. In this case, skip
steps 4 to 6.
If there are any trailing slash characters in
string, they shall be removed.
If there are any slash characters remaining in
string, the prefix of string up to and including the last
slash character in string shall be removed.
If the suffix operand is present, is not identical
to the characters remaining in string, and is identical to a suffix
of the characters remaining in string, the suffix suffix
shall be removed from string. Otherwise, string is not
modified by this step. It shall not be considered an error if
suffix is not found in string.
The resulting string shall be written to standard output.
The following environment variables shall affect the execution of
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, Internationalization
Variables for the precedence of internationalization variables used to
determine the values of locale categories.)
If set to a non-empty string value, override the values of
all the other internationalization variables.
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).
Determine the locale that should be used to affect the
format and contents of diagnostic messages written to standard error.
Determine the location of message catalogs for the
processing of LC_MESSAGES.
The definition of pathname specifies implementation-defined behavior for
pathnames starting 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
produces a filename that could be used to open the file named by string
in the directory returned by:
If the string string is not a valid pathname, the same algorithm is used,
but the result need not be a valid filename. The basename utility is
not expected to make any judgements about the validity of string as a
pathname; it just follows the specified algorithm to produce a result string.
The following shell script compiles /usr/src/cmd/cat.c and moves the
output to a file named cat in the current directory when invoked with
the argument /usr/src/cmd/cat or with the argument
The behaviors of basename and dirname 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 early proposal versions of these utilities due to
the way it specified handling of trailing slashes.
Since the definition of pathname specifies implementation-defined
behavior for pathnames starting with two slash characters, this volume of
IEEE Std 1003.1-2001 specifies similar implementation-defined
behavior for the basename and dirname utilities.
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 original
Standard can be obtained online at http://www.opengroup.org/unix/online.html