1.\" 2.\" Copyright (c) 1997 Shigio Yamaguchi. All rights reserved. 3.\" Copyright (c) 1999 Tama Communications Corporation. All rights reserved. 4.\" 5.\" Redistribution and use in source and binary forms, with or without 6.\" modification, are permitted provided that the following conditions 7.\" are met: 8.\" 1. Redistributions of source code must retain the above copyright 9.\" notice, this list of conditions and the following disclaimer. 10.\" 2. Redistributions in binary form must reproduce the above copyright 11.\" notice, this list of conditions and the following disclaimer in the 12.\" documentation and/or other materials provided with the distribution. 13.\" 14.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 15.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 16.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 17.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 18.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 19.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 20.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 21.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 22.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 23.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 24.\" SUCH DAMAGE. 25.\" 26.\" $FreeBSD$ 27.\" 28.Dd Dec 15, 1997" 29.Dt ABS2REL 3 30.Os 31.Sh NAME 32.Nm abs2rel 33.Nd make a relative path name from an absolute path name 34.Sh SYNOPSIS 35.Ft "char *" 36.Fn abs2rel "const char *path" "const char *base" "char *result" "size_t size" 37.Sh DESCRIPTION 38The 39.Fn abs2rel 40function makes a relative path name from an absolute path name 41.Fa path 42based on a directory 43.Fa base 44and copies the resulting path name into the memory referenced by 45.Fa result . 46The 47.Fa result 48argument must refer to a buffer capable of storing at least 49.Fa size 50characters. 51 52The resulting path name may include symbolic links. 53The 54.Fn abs2rel 55function doesn't check whether or not any path exists. 56.Sh "RETURN VALUES" 57The 58.Fn abs2rel 59function returns relative path name on success. 60If an error occurs, 61it returns 62.Dv NULL . 63.Sh ERRORS 64The 65.Fn abs2rel 66function may fail and set the external variable 67.Va errno 68to indicate the error. 69.Bl -tag -width Er 70.It Bq Er EINVAL 71The 72.Fa base 73directory isn't an absolute path name or the 74.Fa size 75argument is zero. 76.It Bq Er ERANGE 77The 78.Fa size 79argument is greater than zero but smaller than the length of the pathname plus 1. 80.Sh EXAMPLE 81 char result[MAXPATHLEN]; 82 char *path = abs2rel("/usr/src/sys", "/usr/local/lib", result, MAXPATHLEN); 83 84yields: 85 86 path == "../../src/sys" 87 88Similarly, 89 90 path1 = abs2rel("/usr/src/sys", "/usr", result, MAXPATHLEN); 91 path2 = abs2rel("/usr/src/sys", "/usr/src/sys", result, MAXPATHLEN); 92 93yields: 94 95 path1 == "src/sys" 96 path2 == "." 97 98.Sh BUGS 99If the 100.Fa base 101directory includes symbolic links, 102the 103.Fn abs2rel 104function produces the wrong path. 105For example, if '/sys' is a symbolic link to '/usr/src/sys', 106 107 char *path = abs2rel("/usr/local/lib", "/sys", result, MAXPATHLEN); 108 109yields: 110 111 path == "../usr/local/lib" /* It's wrong!! */ 112 113You should convert the base directory into a real path in advance. 114.Pp 115 116 path = abs2rel("/sys/kern", realpath("/sys", resolvedname), result, MAXPATHLEN); 117 118yields: 119 120 path == "../../../sys/kern" /* It's correct but ... */ 121 122That is correct, but a little redundant. If you wish get the simple 123answer 'kern', do the following. 124 125 path = abs2rel(realpath("/sys/kern", r1), realpath("/sys", r2), 126 result, MAXPATHLEN); 127 128The 129.Fn realpath 130function assures correct result, but don't forget that 131.Fn realpath 132requires that all but the last component of the path exist. 133.Sh "SEE ALSO" 134.Xr rel2abs 3 135.Sh AUTHORS 136Shigio Yamaguchi (shigio@tamacom.com) 137