BASENAME(P) POSIX Programmer's Manual BASENAME(P)
basename - return non-directory portion of a pathname
basename string [suffix]
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 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:
1. 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.
2. If string is "//" , it is implementation-defined whether steps 3 to 6 are skipped or
3. If string consists entirely of slash characters, string shall be set to a single slash
character. In this case, skip steps 4 to 6.
4. If there are any trailing slash characters in string, they shall be removed.
5. 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.
6. 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 operands shall be supported:
string A string.
suffix A string.
The following environment variables shall affect the execution of basename:
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 basename 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.
If the string string is a valid pathname:
produces a filename that could be used to open the file named by string in the directory
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 /usr/src/cmd/cat.c:
c99 $(dirname "$1")/$(basename "$1" .c).c
mv a.out $(basename "$1" .c)
The behaviors of basename and dirname have been coordinated so that when string is a valid
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.
Parameters and Variables , dirname()
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 BASENAME(P)