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.
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 volume of POSIX.1‐2017,
Section 3.271,
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 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 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.
None.
The following operands shall be supported:
- string
- A string.
- suffix
- A string.
Not used.
None.
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
POSIX.1‐2017, 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.
Default.
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.
None.
None.
The following exit values shall be returned:
- 0
- Successful completion.
- >0
- An error occurred.
Default.
The following sections are informative.
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.
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 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
/usr/src/cmd/cat.c:
c99 -- "$(dirname -- "$1")/$(basename -- "$1" .c).c" &&
mv a.out "$(basename -- "$1" .c)"
The EXAMPLES section of the
basename() function (see the System
Interfaces volume of POSIX.1‐2017,
basename()) includes a
table showing examples of the results of processing several sample pathnames
by the
basename() and
dirname() functions and by the
basename and
dirname utilities.
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 <slash> characters.
Since the definition of
pathname specifies implementation-defined
behavior for pathnames starting with two <slash> characters, this volume
of POSIX.1‐2017 specifies similar implementation-defined behavior for
the
basename and
dirname utilities.
None.
Section 2.5,
Parameters and Variables,
dirname
The Base Definitions volume of POSIX.1‐2017,
Section 3.271,
Pathname,
Chapter 8,
Environment Variables
The System Interfaces volume of POSIX.1‐2017,
basename(),
dirname()
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1-2017, Standard for Information Technology -- Portable Operating
System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018
Edition, Copyright (C) 2018 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 .
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https://www.kernel.org/doc/man-pages/reporting_bugs.html .