.\" $OpenBSD: vis.3,v 1.29 2012/01/16 04:10:36 guenther Exp $ .\" .\" Copyright (c) 1989, 1991, 1993 .\" The Regents of the University of California. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .Dd $Mdocdate: January 16 2012 $ .Dt VIS 3 .Os .Sh NAME .Nm vis , .Nm strvis , .Nm strnvis , .Nm strvisx .Nd visually encode characters .Sh SYNOPSIS .Fd #include .Fd #include .Ft char * .Fn vis "char *dst" "int c" "int flag" "int nextc" .Ft int .Fn strvis "char *dst" "const char *src" "int flag" .Ft int .Fn strnvis "char *dst" "const char *src" "size_t dstsize" "int flag" .Ft int .Fn strvisx "char *dst" "const char *src" "size_t srclen" "int flag" .Sh DESCRIPTION The .Fn vis function copies into .Fa dst a string which represents the character .Fa c . If .Fa c needs no encoding, it is copied in unaltered. The string is NUL-terminated and a pointer to the end of the string is returned. The maximum length of any encoding is four characters (not including the trailing NUL); thus, when encoding a set of characters into a buffer, the size of the buffer should be four times the number of characters encoded, plus one for the trailing NUL. The .Fa flag parameter is used for altering the default range of characters considered for encoding and for altering the visual representation. The additional character, .Fa nextc , is only used when selecting the .Dv VIS_CSTYLE encoding format (explained below). .Pp The .Fn strvis , .Fn strnvis and .Fn strvisx functions copy into .Fa dst a visual representation of the string .Fa src . .Pp The .Fn strvis function encodes characters from .Fa src up to the first NUL, into a buffer .Fa dst (which must be at least 4 * srclen + 1 long). .Pp The .Fn strnvis function encodes characters from .Fa src up to the first NUL or the end of the buffer .Fa dst , as indicated by .Fa dstsize . .Pp The .Fn strvisx function encodes exactly .Fa srclen characters from .Fa src into a buffer .Fa dst (which must be at least 4 * srclen + 1 long). This is useful for encoding a block of data that may contain NULs. .Pp All three forms NUL-terminate .Fa dst , except for .Fn strnvis when .Fa dstsize is zero, in which case .Fa dst is not touched. .Fn strvis and .Fn strvisx return the number of characters in .Fa dst (not including the trailing NUL). .Fn strnvis returns the length that .Fa dst would become if it were of unlimited size (similar to .Xr snprintf 3 or .Xr strlcpy 3 ) . This can be used to detect truncation but it also means that the return value of .Fn strnvis must not be used without checking it against .Fa dstsize . .Pp The encoding is a unique, invertible representation composed entirely of graphic characters; it can be decoded back into the original form using the .Xr unvis 3 or .Xr strunvis 3 functions. .Pp There are two parameters that can be controlled: the range of characters that are encoded, and the type of representation used. By default, all non-graphic characters except space, tab, and newline are encoded (see .Xr isgraph 3 ) . The following flags alter this: .Bl -tag -width VIS_WHITEX .It Dv VIS_ALL Encode all characters, whether visible or not. .It Dv VIS_GLOB Also encode magic characters recognized by .Xr glob 3 .Pf ( Ql * , .Ql \&? , .Ql \&[ ) and .Ql # . .It Dv VIS_SP Also encode space. .It Dv VIS_TAB Also encode tab. .It Dv VIS_NL Also encode newline. .It Dv VIS_WHITE Synonym for .Dv VIS_SP | VIS_TAB | VIS_NL . .It Dv VIS_SAFE Only encode .Dq unsafe characters. These are control characters which may cause common terminals to perform unexpected functions. Currently this form allows space, tab, newline, backspace, bell, and return -- in addition to all graphic characters -- unencoded. .El .Pp There are three forms of encoding. All forms use the backslash .Ql \e character to introduce a special sequence; two backslashes are used to represent a real backslash. These are the visual formats: .Bl -tag -width VIS_CSTYLE .It (default) Use an .Ql M to represent meta characters (characters with the 8th bit set), and use a caret .Ql ^ to represent control characters (see .Xr iscntrl 3 ) . The following formats are used: .Bl -tag -width xxxxx .It Dv \e^C Represents the control character .Ql C . Spans characters .Ql \e000 through .Ql \e037 , and .Ql \e177 (as .Ql \e^? ) . .It Dv \eM-C Represents character .Ql C with the 8th bit set. Spans characters .Ql \e241 through .Ql \e376 . .It Dv \eM^C Represents control character .Ql C with the 8th bit set. Spans characters .Ql \e200 through .Ql \e237 , and .Ql \e377 (as .Ql \eM^? ) . .It Dv \e040 Represents .Tn ASCII space. .It Dv \e240 Represents Meta-space. .It Dv \e-C Represents character .Ql C . Only used with .Dv VIS_ALL . .El .Pp .It Dv VIS_CSTYLE Use C-style backslash sequences to represent standard non-printable characters. The following sequences are used to represent the indicated characters: .Bd -unfilled -offset indent .Li \ea Tn - BEL No (007) .Li \eb Tn - BS No (010) .Li \ef Tn - NP No (014) .Li \en Tn - NL No (012) .Li \er Tn - CR No (015) .Li \es Tn - SP No (040) .Li \et Tn - HT No (011) .Li \ev Tn - VT No (013) .Li \e0 Tn - NUL No (000) .Ed .Pp When using this format, the .Fa nextc parameter is looked at to determine if a NUL character can be encoded as .Ql \e0 instead of .Ql \e000 . If .Fa nextc is an octal digit, the latter representation is used to avoid ambiguity. .It Dv VIS_OCTAL Use a three digit octal sequence. The form is .Ql \eddd where .Ar d represents an octal digit. .El .Pp There is one additional flag, .Dv VIS_NOSLASH , which inhibits the doubling of backslashes and the backslash before the default format (that is, control characters are represented by .Ql ^C and meta characters as .Ql M-C ) . With this flag set, the encoding is ambiguous and non-invertible. .Sh SEE ALSO .Xr unvis 1 , .Xr vis 1 , .Xr snprintf 3 , .Xr strlcpy 3 , .Xr unvis 3 .Sh HISTORY The .Fn vis , .Fn strvis and .Fn strvisx functions first appeared in .Bx 4.4 . The .Fn strnvis function first appeared in .Ox 2.9 . The .Dv VIS_ALL flag first appeared in .Ox 4.9 .