BASENAME(1)                POSIX Programmer's Manual               BASENAME(1)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NAME
       basename -- return non-directory portion of a pathname

SYNOPSIS
       basename string [[suffix]]

DESCRIPTION
       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.

OPTIONS
       None.

OPERANDS
       The following operands shall be supported:

       string    A string.

       suffix    A string.

STDIN
       Not used.

INPUT FILES
       None.

ENVIRONMENT VARIABLES
       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.

ASYNCHRONOUS EVENTS
       Default.

STDOUT
       The basename 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
       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
       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.

RATIONALE
       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
       volume of POSIX.1-2017 specifies similar implementation-defined
       behavior for the basename and dirname utilities.

FUTURE DIRECTIONS
       None.

SEE ALSO
       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()

COPYRIGHT
       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 .

       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.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                          BASENAME(1)
