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 August 7, 2022 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 EXAMPLES 64 char result[MAXPATHLEN]; 65 char *path = abs2rel("/usr/src/sys", "/usr/local/lib", result, MAXPATHLEN); 66 67yields: 68 69 path == "../../src/sys" 70 71Similarly, 72 73 path1 = abs2rel("/usr/src/sys", "/usr", result, MAXPATHLEN); 74 path2 = abs2rel("/usr/src/sys", "/usr/src/sys", result, MAXPATHLEN); 75 76yields: 77 78 path1 == "src/sys" 79 path2 == "." 80.Sh ERRORS 81The 82.Fn abs2rel 83function may fail and set the external variable 84.Va errno 85to indicate the error. 86.Bl -tag -width Er 87.It Bq Er EINVAL 88The 89.Fa base 90directory isn't an absolute path name or the 91.Fa size 92argument is zero. 93.It Bq Er ERANGE 94The 95.Fa size 96argument is greater than zero but smaller than the length of the pathname plus 1. 97 98.Sh SEE ALSO 99.Xr rel2abs 3 100.Sh AUTHORS 101.An Shigio Yamaguchi (shigio@tamacom.com) 102.Sh BUGS 103If the 104.Fa base 105directory includes symbolic links, 106the 107.Fn abs2rel 108function produces the wrong path. 109For example, if '/sys' is a symbolic link to '/usr/src/sys', 110 111 char *path = abs2rel("/usr/local/lib", "/sys", result, MAXPATHLEN); 112 113yields: 114 115 path == "../usr/local/lib" /* It's wrong!! */ 116 117You should convert the base directory into a real path in advance. 118.Pp 119 120 path = abs2rel("/sys/kern", realpath("/sys", resolvedname), result, MAXPATHLEN); 121 122yields: 123 124 path == "../../../sys/kern" /* It's correct but ... */ 125 126That is correct, but a little redundant. 127If you wish get the simple answer 'kern', do the following. 128 129 path = abs2rel(realpath("/sys/kern", r1), realpath("/sys", r2), 130 result, MAXPATHLEN); 131 132The 133.Fn realpath 134function assures correct result, but don't forget that 135.Fn realpath 136requires that all but the last component of the path exist. 137