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.Dd August 7, 2022 27.Dt ABS2REL 3 28.Os 29.Sh NAME 30.Nm abs2rel 31.Nd make a relative path name from an absolute path name 32.Sh SYNOPSIS 33.Ft "char *" 34.Fn abs2rel "const char *path" "const char *base" "char *result" "size_t size" 35.Sh DESCRIPTION 36The 37.Fn abs2rel 38function makes a relative path name from an absolute path name 39.Fa path 40based on a directory 41.Fa base 42and copies the resulting path name into the memory referenced by 43.Fa result . 44The 45.Fa result 46argument must refer to a buffer capable of storing at least 47.Fa size 48characters. 49 50The resulting path name may include symbolic links. 51The 52.Fn abs2rel 53function doesn't check whether or not any path exists. 54.Sh "RETURN VALUES" 55The 56.Fn abs2rel 57function returns relative path name on success. 58If an error occurs, 59it returns 60.Dv NULL . 61.Sh EXAMPLES 62 char result[MAXPATHLEN]; 63 char *path = abs2rel("/usr/src/sys", "/usr/local/lib", result, MAXPATHLEN); 64 65yields: 66 67 path == "../../src/sys" 68 69Similarly, 70 71 path1 = abs2rel("/usr/src/sys", "/usr", result, MAXPATHLEN); 72 path2 = abs2rel("/usr/src/sys", "/usr/src/sys", result, MAXPATHLEN); 73 74yields: 75 76 path1 == "src/sys" 77 path2 == "." 78.Sh ERRORS 79The 80.Fn abs2rel 81function may fail and set the external variable 82.Va errno 83to indicate the error. 84.Bl -tag -width Er 85.It Bq Er EINVAL 86The 87.Fa base 88directory isn't an absolute path name or the 89.Fa size 90argument is zero. 91.It Bq Er ERANGE 92The 93.Fa size 94argument is greater than zero but smaller than the length of the pathname plus 1. 95 96.El 97.Sh SEE ALSO 98.Xr rel2abs 3 99.Sh AUTHORS 100.An Shigio Yamaguchi (shigio@tamacom.com) 101.Sh BUGS 102If the 103.Fa base 104directory includes symbolic links, 105the 106.Fn abs2rel 107function produces the wrong path. 108For example, if '/sys' is a symbolic link to '/usr/src/sys', 109 110 char *path = abs2rel("/usr/local/lib", "/sys", result, MAXPATHLEN); 111 112yields: 113 114 path == "../usr/local/lib" /* It's wrong!! */ 115 116You should convert the base directory into a real path in advance. 117.Pp 118 119 path = abs2rel("/sys/kern", realpath("/sys", resolvedname), result, MAXPATHLEN); 120 121yields: 122 123 path == "../../../sys/kern" /* It's correct but ... */ 124 125That is correct, but a little redundant. 126If you wish get the simple answer 'kern', do the following. 127 128 path = abs2rel(realpath("/sys/kern", r1), realpath("/sys", r2), 129 result, MAXPATHLEN); 130 131The 132.Fn realpath 133function assures correct result, but don't forget that 134.Fn realpath 135requires that all but the last component of the path exist. 136