man-pages/man3/basename.3

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.TH DIRNAME 3  2000-12-14 "GNU" "Linux Programmer's Manual"
.SH NAME
dirname, basename \- Parse pathname components
.SH SYNOPSIS
.nf
.B #include <libgen.h>
.sp
.BI "char *dirname(char *" path );
.br
.BI "char *basename(char *" path );
.fi
.SH DESCRIPTION
Warning: there are two different functions
.BR basename ()
- see below.
.LP
The functions
.BR dirname ()
and
.BR basename ()
break a null-terminated pathname string into directory 
and filename components.  
In the usual case, 
.BR dirname ()
returns the string up to, but not including, the final '/', and
.BR basename ()
returns the component following the final '/'.
Trailing '/' characters are not counted as part of the pathname.
.PP
If 
.I path
does not contain a slash,
.BR dirname ()
returns the string "." while
.BR basename ()
returns a copy of
.IR path .
If 
.I path
is the string "/", then both
.BR dirname ()
and 
.BR basename ()
return the string "/".
If 
.I path
is a NULL pointer or points to an empty string, then both
.BR dirname ()
and
.BR basename ()
return the string ".".
.PP
Concatenating the string returned by
.BR dirname (),
a "/", and the string returned by 
.BR basename ()
yields a complete pathname.
.PP
Both 
.BR dirname ()
and
.BR basename ()
may modify the contents of 
.IR path , 
so a copy should be passed when calling one of these functions.
(Because either function may return a pointer to some part of
.IR path ,
the copy should not be freed until the pointer returned by
the function is no longer required.)
Furthermore, 
.BR dirname ()
and
.BR basename ()
may return pointers to statically allocated memory
which may be overwritten by subsequent calls.
.PP
The following list of examples (taken from SUSv2)
shows the strings returned by 
.BR dirname ()
and
.BR basename ()
for different paths:
.sp
.nf
.B 
path  		dirname		basename
"/usr/lib"	"/usr"		"lib"
"/usr/"		"/"  		"usr"
"usr"		"."  		"usr"
"/"  		"/"  		"/"
"."  		"."  		"."
".."  		"."  		".."
.fi
.SH EXAMPLE
.RS
.nf
char *dirc, *basec, *bname, *dname;
char *path = "/etc/passwd";

dirc = strdup(path);
basec = strdup(path);
dname = dirname(dirc);
bname = basename(basec);
printf("dirname=%s, basename=%s\\n", dname, bname);
.fi
.RE
.SH "RETURN VALUE"
Both 
.BR dirname ()
and
.BR basename ()
return pointers to null-terminated strings.
.SH NOTES
There are two different versions of
.BR basename ()
- the POSIX version described above, and the GNU version, which one gets
after
.br
.nf

.B "    #define _GNU_SOURCE"
.br
.B "    #include <string.h>"

.fi
The GNU version never modifies its argument, and returns the
empty string when
.I path
has a trailing slash, and in particular also when it is "/".
There is no GNU version of
.BR dirname ().
.LP
With glibc, one gets the POSIX version of
.BR basename ()
when <libgen.h> is included, and the GNU version otherwise.
.SH BUGS
In the glibc implementation of the POSIX versions of these functions
they modify their argument, and segfault when called with a static string
like "/usr/".
Before glibc 2.2.1, the glibc version of
.BR dirname ()
did not correctly handle pathnames with trailing '/' characters,
and generated a segfault if given a NULL argument.
.SH "CONFORMING TO"
POSIX.1-2001
.SH "SEE ALSO"
.BR basename (1),
.BR dirname (1),
.BR feature_test_macros (7)