BASENAME(1P) POSIX Programmer's Manual BASENAME(1P)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.
NAMEbasename — return non-directory portion of a pathname
SYNOPSISbasename string [suffix]
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 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
2. If string is "//", it is implementation-defined whether steps 3 to
6 are skipped or processed.
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
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 charac‐
ters remaining in string, and is identical to a suffix of the char‐
acters 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 base‐
LANG Provide a default value for the internationalization vari‐
ables that are unset or null. (See the Base Definitions vol‐
ume of POSIX.1‐2008, Section 8.2, Internationalization Vari‐
ables 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).
Determine the locale that should be used to affect the format
and contents of diagnostic messages written to standard
NLSPATH Determine the location of message catalogs for the processing
The basename utility shall write a line to the standard output in the
"%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 starting with two <slash> characters. Therefore, applica‐
tions 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.
If the string string is a valid pathname:
$(basename -- "string")
produces a filename that could be used to open the file named by string
in the directory returned by:
$(dirname -- "string")
If the string string is not a valid pathname, the same algorithm is
used, but the result need not be a valid filename. The basename utility
is not expected to make any judgements about the validity of string as
a pathname; it just follows the specified algorithm to produce a result
The following shell script compiles /usr/src/cmd/cat.c and moves the
output to a file named cat in the current directory when invoked with
the argument /usr/src/cmd/cat or with the argument /usr/src/cmd/cat.c:
c99 -- "$(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 pathname:
$(basename -- "string")
would be a valid filename for the file in the directory:
$(dirname -- "string")
This would not work for the early proposal versions of these utilities
due to the way it specified handling of trailing <slash> characters.
Since the definition of pathname specifies implementation-defined
behavior for pathnames starting with two <slash> characters, this vol‐
ume of POSIX.1‐2008 specifies similar implementation-defined behavior
for the basename and dirname utilities.
Section 2.5, Parameters and Variables, dirname
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 Electri‐
cal 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 .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the source
files to man page format. To report such errors, see https://www.ker‐
IEEE/The Open Group 2013 BASENAME(1P)