man3/basename.3

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  25 .\" Created, 14 Dec 2000 by Michael Kerrisk
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  27 .TH BASENAME 3  2019-03-06 "GNU" "Linux Programmer's Manual"
  28 .SH NAME
  29 basename, dirname \- parse pathname components
  30 .SH SYNOPSIS
  31 .nf
  32 .B #include <libgen.h>
  33 .PP
  34 .BI "char *dirname(char *" path );
  35 .PP
  36 .BI "char *basename(char *" path );
  37 .fi
  38 .SH DESCRIPTION
  39 Warning: there are two different functions
  40 .BR basename ()
  41 - see below.
  42 .PP
  43 The functions
  44 .BR dirname ()
  45 and
  46 .BR basename ()
  47 break a null-terminated pathname string into directory
  48 and filename components.
  49 In the usual case,
  50 .BR dirname ()
  51 returns the string up to, but not including, the final \(aq/\(aq, and
  52 .BR basename ()
  53 returns the component following the final \(aq/\(aq.
  54 Trailing \(aq/\(aq characters are not counted as part of the pathname.
  55 .PP
  56 If
  57 .I path
  58 does not contain a slash,
  59 .BR dirname ()
  60 returns the string "." while
  61 .BR basename ()
  62 returns a copy of
  63 .IR path .
  64 If
  65 .I path
  66 is the string "/", then both
  67 .BR dirname ()
  68 and
  69 .BR basename ()
  70 return the string "/".
  71 If
  72 .I path
  73 is a null pointer or points to an empty string, then both
  74 .BR dirname ()
  75 and
  76 .BR basename ()
  77 return the string ".".
  78 .PP
  79 Concatenating the string returned by
  80 .BR dirname (),
  81 a "/", and the string returned by
  82 .BR basename ()
  83 yields a complete pathname.
  84 .PP
  85 Both
  86 .BR dirname ()
  87 and
  88 .BR basename ()
  89 may modify the contents of
  90 .IR path ,
  91 so it may be desirable to pass a copy when calling one of
  92 these functions.
  93 .PP
  94 These functions may return pointers to statically allocated memory
  95 which may be overwritten by subsequent calls.
  96 Alternatively, they may return a pointer to some part of
  97 .IR path ,
  98 so that the string referred to by
  99 .I path
 100 should not be modified or freed until the pointer returned by
 101 the function is no longer required.
 102 .PP
 103 The following list of examples (taken from SUSv2)
 104 shows the strings returned by
 105 .BR dirname ()
 106 and
 107 .BR basename ()
 108 for different paths:
 109 .RS
 110 .TS
 111 lb lb lb
 112 l l l l.
 113 path            dirname basename
 114 /usr/lib        /usr    lib
 115 /usr/           /       usr
 116 usr             .       usr
 117 /               /       /
 118 \&.             .       .
 119 \&..            .       ..
 120 .TE
 121 .RE
 122 .SH RETURN VALUE
 123 Both
 124 .BR dirname ()
 125 and
 126 .BR basename ()
 127 return pointers to null-terminated strings.
 128 (Do not pass these pointers to
 129 .BR free (3).)
 130 .SH ATTRIBUTES
 131 For an explanation of the terms used in this section, see
 132 .BR attributes (7).
 133 .TS
 134 allbox;
 135 lbw21 lb lb
 136 l l l.
 137 Interface       Attribute       Value
 138 T{
 139 .BR basename (),
 140 .BR dirname ()
 141 T}      Thread safety   MT-Safe
 142 .TE
 143 .SH CONFORMING TO
 144 POSIX.1-2001, POSIX.1-2008.
 145 .SH NOTES
 146 There are two different versions of
 147 .BR basename ()
 148 - the POSIX version described above, and the GNU version, which one gets
 149 after
 150 .PP
 151 .in +4n
 152 .EX
 153 .BR "    #define _GNU_SOURCE" "         /* See feature_test_macros(7) */"
 154 .B "    #include <string.h>"
 155 .EE
 156 .in
 157 .PP
 158 The GNU version never modifies its argument, and returns the
 159 empty string when
 160 .I path
 161 has a trailing slash, and in particular also when it is "/".
 162 There is no GNU version of
 163 .BR dirname ().
 164 .PP
 165 With glibc, one gets the POSIX version of
 166 .BR basename ()
 167 when
 168 .I <libgen.h>
 169 is included, and the GNU version otherwise.
 170 .SH BUGS
 171 In the glibc implementation,
 172 the POSIX versions of these functions modify the
 173 .I path
 174 argument, and segfault when called with a static string
 175 such as "/usr/".
 176 .PP
 177 Before glibc 2.2.1, the glibc version of
 178 .BR dirname ()
 179 did not correctly handle pathnames with trailing \(aq/\(aq characters,
 180 and generated a segfault if given a NULL argument.
 181 .SH EXAMPLE
 182 The following code snippet demonstrates the use of
 183 .BR basename ()
 184 and
 185 .BR dirname ():
 186 .in +4n
 187 .EX
 188 char *dirc, *basec, *bname, *dname;
 189 char *path = "/etc/passwd";
 190
 191 dirc = strdup(path);
 192 basec = strdup(path);
 193 dname = dirname(dirc);
 194 bname = basename(basec);
 195 printf("dirname=%s, basename=%s\en", dname, bname);
 196 .EE
 197 .in
 198 .SH SEE ALSO
 199 .BR basename (1),
 200 .BR dirname (1)