{ "mode": "man", "parameter": "MHSHOW", "section": "1mh", "url": "https://www.chedong.com/phpMan.php/man/MHSHOW/1mh/json", "generated": "2026-05-30T07:09:20Z", "synopsis": "mhshow [-help] [-version] [+folder] [msgs] [-file file] [-part number] ... [-type content]\n... [-prefer content] ... [-noprefer] [-concat | -noconcat] [-textonly | -notextonly]\n[-inlineonly | -noinlineonly] [-header | -noheader] [-form formfile] [-markform form‐\nfile] [-rcache policy] [-wcache policy] [-check | -nocheck]", "sections": { "NAME": { "content": "mhshow - display nmh MIME messages\n", "subsections": [] }, "SYNOPSIS": { "content": "mhshow [-help] [-version] [+folder] [msgs] [-file file] [-part number] ... [-type content]\n... [-prefer content] ... [-noprefer] [-concat | -noconcat] [-textonly | -notextonly]\n[-inlineonly | -noinlineonly] [-header | -noheader] [-form formfile] [-markform form‐\nfile] [-rcache policy] [-wcache policy] [-check | -nocheck]\n", "subsections": [] }, "DESCRIPTION": { "content": "The mhshow command displays contents of a MIME (multi-media) message, or collection of mes‐\nsages.\n\nmhshow manipulates multi-media messages as specified in RFC 2045 to RFC 2049. Currently\nmhshow only supports encodings in message bodies, and does not support the encoding of mes‐\nsage headers as specified in RFC 2047.\n\nBy default, mhshow will display only the text parts of a message that are not marked as at‐\ntachments. This behavior can be changed by the -notextonly and -noinlineonly switches. In\naddition, by using the -part, -type, and -prefer switches, you may limit and reorder the set\nof parts to be displayed, based on part number and/or content type. The inclusion of any", "subsections": [ { "name": "-part -type -textonly -inlineonly.", "content": "The -header switch controls whether mhshow will print a message separator header before each\nmessage that it displays. The header format can be controlled using -headerform, to specify\na file containing mh-format(5) instructions. A copy of the built-in default headerform can\nbe found in /etc/nmh/mhshow.header, for reference. In addition to the normal set of mh-for‐\nmat(5) instructions, a \"%{folder}\" escape provides a string representing the current folder.\n\nBy default, mhshow will concatenate all content under one pager. If you want each part to be\ndisplayed separately, you can override the default behavior with -noconcat.\n\nThe -file file switch directs mhshow to use the specified file as the source message, rather\nthan a message from a folder. If you specify this file as “-”, then mhshow will accept the\nsource message on the standard input. Note that the file, or input from standard input,\nshould be a validly formatted message, just like any other nmh message. It should not be in\nmail drop format (to convert a file in mail drop format to a folder of nmh messages, see\ninc(1)).\n\nThe -part switch can be given (one or more times) to restrict the set of subparts that will\nbe displayed. (Obviously with no -part switches, all parts will be considered.) If a -part\nswitch specifies a specific subpart (i.e., a \"leaf\" in the tree of MIME parts), then that\npart will always be displayed. If a -part switch references a multipart/alternative part,\nthen (in the absence of a -type switch) only the default subpart of that multipart will be\ndisplayed.\n\nA part specification consists of a series of numbers separated by dots. For example, in a\nmultipart content containing three parts, these would be named as 1, 2, and 3, respectively.\nIf part 2 was also a multipart content containing two parts, these would be named as 2.1 and\n2.2, respectively. Note that the -part switch is effective only for messages containing a\nmultipart content. If a message has some other kind of content, or if the part is itself an‐\nother multipart content, the -part switch will not prevent the content from being acted upon.\n\nThe -type switch can also be used to restrict (or, when used in conjunction with -part, to\nfurther restrict) the display of parts according to content type. One or more -type switches\npart will only select the first match from a multipart/alternative, even if there is more\nthan one subpart that matches (one of) the given content type(s).\n\nUsing either -part or -type switches alone will cause either switch to select the part(s)\nthey match. Using them together will select only the part(s) matched by both (sets of)\nswitches. In other words, the result is the intersection, and not the union, of their sepa‐\nrate match results.\n\nA content specification consists of a content type and a subtype. The initial list of “stan‐\ndard” content types and subtypes can be found in RFC 2046.\n\nA list of commonly used contents is briefly reproduced here:\n\nType Subtypes\n---- --------\ntext plain, enriched\nmultipart mixed, alternative, digest, parallel\nmessage rfc822, partial, external-body\napplication octet-stream, postscript\nimage jpeg, gif, png\naudio basic\nvideo mpeg\n\nA legal MIME message must contain a subtype specification.\n\nTo specify a content, regardless of its subtype, just use the name of the content, e.g., “au‐\ndio”. To specify a specific subtype, separate the two with a slash, e.g., “audio/basic”.\nNote that regardless of the values given to the -type switch, a multipart content (of any\nsubtype listed above) is always acted upon. Further note that if the -type switch is used,\nand it is desirable to act on a message/external-body content, then the -type switch must be\nused twice: once for message/external-body and once for the content externally referenced.\n\nIn the absence of -prefer, mhshow will select the \"best\" displayable subpart from multi‐\npart/alternative content. The -prefer switch can be used (one or more times, in order of as‐\ncending preference) to let MH know which content types from a multipart/alternative MIME part\nare preferred by the user, in order to override the default selection for display. For exam‐\nple, mail is often sent containing both plaintext and HTML-formatted versions of the same\ncontent, and the HTML version is usually indicated to be the \"best\" format for viewing. Us‐\ning “-prefer text/plain” will cause the plaintext version to be displayed if possible, but\nstill allow display of the HTML part if there is no plaintext subpart available. Using\n“-prefer text/plain -prefer image/png” would add a preference for PNG images, which might or\nmight not ever appear in the same multipart/alternative section with text/plain. Implementa‐\ntion note: RFC 2046 requires that the subparts of a multipart/alternative be ordered accord‐\ning to \"faithfulness to the original content\", and MH by default selects the subpart ranked\nmost \"faithful\" by that ordering. The -prefer switch reorders the alternative parts (only\ninternally, never changing the message file) to move the user's preferred part(s) to the\n\"most faithful\" position. Thus, when viewed by mhlist, the ordering of multipart/alternative\nparts will appear to change when invoked with or without various -prefer switches. Since the\nlast of multiple -prefer options \"wins\", a -prefer on the command line will override any in a\nprofile entry.\n\nThe -noprefer switch will cancel any previous -prefer switches.\n" }, { "name": "Unseen Sequence", "content": "If the profile entry “Unseen-Sequence” is present and non-empty, then mhshow will remove each\nof the messages shown from each sequence named by the profile entry.\n" }, { "name": "Checking the Contents", "content": "The -check switch tells mhshow to check each content for an integrity checksum. If a content\nhas such a checksum (specified as a Content-MD5 header field), then mhshow will attempt to\nverify the integrity of the content.\n" }, { "name": "Showing the Contents", "content": "The headers of each message are displayed with the mhlproc (usually mhl), using the standard\nformat file, mhl.headers. You may specify an alternative format file with the -form formfile\nswitch. If the format file mhl.null is specified, then the display of the message headers is\nsuppressed.\n\nNext, the contents are extracted from the message and are stored in a temporary file. Usu‐\nally, the name of the temporary file is the word “mhshow” followed by a string of characters.\nOccasionally, the method used to display a content (described next), requires that the file\nend in a specific suffix. For example, the soffice command (part of the StarOffice package)\ncan be used to display Microsoft Word content, but it uses the suffix to determine how to\ndisplay the file. If no suffix is present, the file is not correctly loaded. Similarly,\nolder versions of the gs command append a “.ps” suffix to the filename if one was missing.\nAs a result, these cannot be used to read the default temporary file.\n\nTo get around this, your profile can contain lines of the form:\n\nmhshow-suffix-/: \n\nor\n\nmhshow-suffix-: \n\nto specify a suffix which can be automatically added to the temporary file created for a spe‐\ncific content type. For example, the following lines might appear in your profile:\n\nmhshow-suffix-text: .txt\nmhshow-suffix-application/msword: .doc\nmhshow-suffix-application/PostScript: .ps\n\nto automatically append a suffix to the temporary files.\n\nThe method used to display the different contents in the messages bodies will be determined\nby a “display string”. To find the display string, mhshow will first search your profile for\nan entry of the form:\n\nmhshow-show-/\n\nIf this isn't found, mhshow will search for an entry of the form:\n\nmhshow-show-\n\nto determine the display string.\n\nIf a display string is found, any escapes (given below) will be expanded. The result will be\nexecuted under “/bin/sh”, with the standard input set to the content.\n\nThe display string may contain the following escapes:\n\n%a Insert parameters from Content-Type field\n%{parameter} Insert the parameter value from the Content-Type field\n%f Insert filename containing content\n%F %f, and stdin is terminal not content\n%l display listing prior to displaying content\n%s Insert content subtype\n%d Insert content description\n%% Insert the character %\n\nmhshow will execute at most one display string at any given time, and wait for the current\ndisplay string to finish execution before executing the next display string.\n\nThe {parameter} escape is typically used in a command line argument that should only be\npresent if it has a non-null value. It is highly recommended that the entire escape be\nwrapped in double quotes. Shell parameter expansion can construct the argument only when it\nis non-null, e.g.,\n\nmhshow-show-text/html: charset=\"%{charset}\";\nw3m ${charset:+-I $charset} -T text/html %F\n\nThat example also shows the use of indentation to signify continuation: the two text lines\ncombine to form a single entry. Note that when dealing with text that has been converted in‐\nternally by iconv(3), the “charset” parameter will reflect the target character set of the\ntext, rather than the original character set in the message.\n\nNote that if the content being displayed is multipart, but not one of the subtypes listed\nabove, then the f- and F-escapes expand to multiple filenames, one for each subordinate con‐\ntent. Furthermore, stdin is not redirected from the terminal to the content.\n\nIf a display string is not found, mhshow behaves as if these profile entries were supplied\nand supported:\n\nmhshow-show-text/plain: %lmoreproc %F\nmhshow-show-message/rfc822: %lshow -file %F\n\nNote that “moreproc” is not supported in user profile display strings.\n\nIf a subtype of type text doesn't have a profile entry, it will be treated as text/plain.\n\nmhshow has default methods for handling multipart messages of subtype mixed, alternative,\nparallel, and digest. Any unknown subtype of type multipart (without a profile entry), will\nbe treated as multipart/mixed.\n\nIf none of these apply, then mhshow will check to see if the message has an applica‐\ntion/octet-stream content with parameter “type=tar”. If so, mhshow will use an appropriate\ncommand. If not, mhshow will complain.\n\nExample entries might be:\n\nmhshow-show-audio/basic: raw2audio 2>/dev/null | play\nmhshow-show-image: xv %f\nmhshow-show-application/PostScript: lpr -Pps\n\nIf an f- or F-escape is not quoted with single quotes, its expansion will be wrapped with\nsingle quotes.\n\nFinally, mhshow will process each message serially -- it won't start showing the next message\nuntil all the commands executed to display the current message have terminated.\n" }, { "name": "Showing Alternate Character Sets", "content": "If mhshow was built with iconv(3), then all text/plain parts of the message(s) will be dis‐\nplayed using the character set of the current locale. See the mhparam(1) man page for how to\ndetermine whether your nmh installation includes iconv(3) support. To convert text parts\nother than text/plain, or if mhshow was not built with iconv, an external program can be\nused, as described next.\n\nBecause a content of type text might be in a non-ASCII character set, when mhshow encounters\na “charset” parameter for this content, it checks if your terminal can display this character\nset natively. mhshow checks this by examining the current character set defined by the lo‐\ncale(1) environment variables. If the value of the locale character set is equal to the\nvalue of the charset parameter, then mhshow assumes it can display this content without any\nadditional setup. If the locale is not set properly, mhshow will assume a value of “US-\nASCII”. If the character set cannot be displayed natively, then mhshow will look for an en‐\ntry of the form:\n\nmhshow-charset-\n\nwhich should contain a command creating an environment to render the character set. This\ncommand string should containing a single “%s”, which will be filled-in with the command to\ndisplay the content.\n\nExample entries might be:\n\nmhshow-charset-iso-8859-1: xterm -fn '-*-*-medium-r-normal-*-*-120-*-*-c-*-iso8859-*' -e\n%s\n\nor\n\nmhshow-charset-iso-8859-1: '%s'\n\nThe first example tells mhshow to start xterm and load the appropriate character set for that\nmessage content. The second example tells mhshow that your pager (or other program handling\nthat content type) can handle that character set, and that no special processing is needed\nbeforehand.\n\nNote that many pagers strip off the high-order bit, or have problems displaying text with the\nhigh-order bit set. However, the pager less has support for single-octet character sets.\nFor example, messages encoded in the ISO-8859-1 character set can be viewed using less, with\nthese environment variable settings:\n\nLESSCHARSET latin1\nLESS -f\n\nThe first setting tells less to use the ISO-8859-1 definition to determine whether a charac‐\nter is “normal”, “control“, or “binary”. The second setting tells less not to warn you if it\nencounters a file that has non-ASCII characters. Then, simply set the moreproc profile entry\nto less, and it will get called automatically. (To handle other single-octet character sets,\nlook at the less(1) manual entry for information about the LESSCHARDEF environment variable.)\n" }, { "name": "Messages of Type message/partial", "content": "mhshow cannot directly display messages of type partial. You must first reassemble them into\na normal message using mhstore. Check mhstore(1) for details.\n" }, { "name": "External Access", "content": "For contents of type message/external-body, mhshow supports these access-types:\n\n• afs\n\n• anon-ftp\n\n• ftp\n\n• local-file\n\n• mail-server\n\n• url\n\nFor the “anon-ftp” and “ftp” access types, mhshow will look for the “nmh-access-ftp” profile\nentry, e.g.,\n\nnmh-access-ftp: myftp.sh\n\nto determine the pathname of a program to perform the FTP retrieval.\n\nThis program is invoked with these arguments:\n\ndomain name of FTP-site\nusername\npassword\nremote directory\nremote filename\nlocal filename\n“ascii” or “binary”\n\nThe program should terminate with an exit status of zero if the retrieval is successful, and\na non-zero exit status otherwise.\n\nFor the “url” access-type, mhshow will look for the “nmh-access-url” profile entry. See mh‐\nstore(1) for more details.\n" }, { "name": "The Content Cache", "content": "When mhshow encounters an external content containing a “Content-ID:” field, and if the con‐\ntent allows caching, then depending on the caching behavior of mhshow, the content might be\nread from or written to a cache.\n\nThe caching behavior of mhshow is controlled with the -rcache and -wcache switches, which de‐\nfine the policy for reading from, and writing to, the cache, respectively. One of four poli‐\ncies may be specified: “public”, indicating that mhshow should make use of a publicly-acces‐\nsible content cache; “private”, indicating that mhshow should make use of the user's private\ncontent cache; “never”, indicating that mhshow should never make use of caching; and, “ask”,\nindicating that mhshow should ask the user.\n\nThere are two directories where contents may be cached: the profile entry “nmh-cache” names a\ndirectory containing world-readable contents, and, the profile entry “nmh-private-cache”\nnames a directory containing private contents. The former should be an absolute (rooted) di‐\nrectory name.\n\nFor example,\n\nnmh-cache: /tmp\n\nmight be used if you didn't care that the cache got wiped after each reboot of the system.\nThe latter is interpreted relative to the user's nmh directory, if not rooted, e.g.,\n\nnmh-private-cache: .cache\n\n(which is the default value).\n" }, { "name": "User Environment", "content": "Because the display environment in which mhshow operates may vary for different machines,\nmhshow will look for the environment variable MHSHOW. If present, this specifies the name of\nan additional user profile which should be read. Hence, when a user logs in on a particular\ndisplay device, this environment variable should be set to refer to a file containing defini‐\ntions useful for the given display device. Normally, only entries that deal with the methods\nto display different content type and subtypes\n\nmhshow-show-/\nmhshow-show-\n\nneed be present in this additional profile. Finally, mhshow will attempt to consult\n\n/etc/nmh/mhn.defaults\n\nwhich is created automatically during nmh installation.\n\nSee \"Profile Lookup\" in mh-profile(5) for the profile search order, and for how duplicate en‐\ntries are treated.\n" }, { "name": "Content-Type Marker", "content": "mhshow will display a marker containing information about the part being displayed next. The\ndefault marker can be changed using the -markform switch to specify a file containing mh-for‐\nmat(5) instructions to use when displaying the content marker. A copy of the default mark‐\nform can be found in /etc/nmh/mhshow.marker, for reference. In addition to the normal set of\nmh-format(5) instructions, the following component escapes are supported:\n\nEscape Returns Description\npart string MIME part number\ncontent-type string MIME Content-Type of part\ndescription string Content-Description header\ndisposition string Content disposition (attachment or inline)\nctype- string Value of from Content-Type header\ncdispo- string Value of from\nContent-Disposition header\n%(size) integer The size of the decoded part, in bytes\n%(unseen) boolean Returns true for suppressed parts\nIn this context, the %(unseen) function indicates whether mhshow has decided to not dis‐\nplay a particular part due to the -textonly or -inlineonly switches.\nAll MIME parameters and the “Content-Description” header will have RFC 2231 decoding applied\nand be converted to the local character set.\n" } ] }, "FILES": { "content": "mhshow looks for all format files and mhn.defaults in multiple locations: absolute pathnames\nare accessed directly, tilde expansion is done on usernames, and files are searched for in\nthe user's Mail directory, as specified in their profile. If not found there, the directory\n“/etc/nmh” is checked.\n\n$HOME/.mhprofile The user profile\n$MHSHOW Additional profile entries\n/etc/nmh/mhn.defaults System default MIME profile entries\n/etc/nmh/mhl.headers The headers template\n/etc/nmh/mhshow.marker Example content marker\n/etc/nmh/mhshow.header Example message separator header\n", "subsections": [] }, "PROFILE COMPONENTS": { "content": "Path: To determine the user's nmh directory\nCurrent-Folder: To find the default current folder\nUnseen-Sequence: To name sequences denoting unseen messages\nmhlproc: Default program to display message headers\nnmh-access-ftp: Program to retrieve contents via FTP\nnmh-access-url: Program to retrieve contents via HTTP\nnmh-cache Public directory to store cached external contents\nnmh-private-cache Personal directory to store cached external contents\nmhshow-charset-* Template for displaying contents\nmoreproc: Default program to display text/plain content\n", "subsections": [] }, "SEE ALSO": { "content": "iconv(3), mhbuild(1), mhl(1), mhlist(1), mhparam(1), mhstore(1), sendfiles(1)\n", "subsections": [] }, "DEFAULTS": { "content": "`+folder' defaults to the current folder\n`msgs' defaults to cur\n`-nocheck'\n`-concat'\n`-textonly'\n`-inlineonly'\n`-form mhl.headers'\n`-rcache ask'\n`-wcache ask'\n", "subsections": [] }, "CONTEXT": { "content": "If a folder is given, it will become the current folder. The last message selected will be‐\ncome the current message.\n\n\n\nnmh-1.7.1 2015-02-08 MHSHOW(1mh)", "subsections": [] } }, "summary": "mhshow - display nmh MIME messages", "flags": [ { "flag": "", "long": null, "arg": null, "description": "The -header switch controls whether mhshow will print a message separator header before each message that it displays. The header format can be controlled using -headerform, to specify a file containing mh-format(5) instructions. A copy of the built-in default headerform can be found in /etc/nmh/mhshow.header, for reference. In addition to the normal set of mh-for‐ mat(5) instructions, a \"%{folder}\" escape provides a string representing the current folder. By default, mhshow will concatenate all content under one pager. If you want each part to be displayed separately, you can override the default behavior with -noconcat. The -file file switch directs mhshow to use the specified file as the source message, rather than a message from a folder. If you specify this file as “-”, then mhshow will accept the source message on the standard input. Note that the file, or input from standard input, should be a validly formatted message, just like any other nmh message. It should not be in mail drop format (to convert a file in mail drop format to a folder of nmh messages, see inc(1)). The -part switch can be given (one or more times) to restrict the set of subparts that will be displayed. (Obviously with no -part switches, all parts will be considered.) If a -part switch specifies a specific subpart (i.e., a \"leaf\" in the tree of MIME parts), then that part will always be displayed. If a -part switch references a multipart/alternative part, then (in the absence of a -type switch) only the default subpart of that multipart will be displayed. A part specification consists of a series of numbers separated by dots. For example, in a multipart content containing three parts, these would be named as 1, 2, and 3, respectively. If part 2 was also a multipart content containing two parts, these would be named as 2.1 and 2.2, respectively. Note that the -part switch is effective only for messages containing a multipart content. If a message has some other kind of content, or if the part is itself an‐ other multipart content, the -part switch will not prevent the content from being acted upon. The -type switch can also be used to restrict (or, when used in conjunction with -part, to further restrict) the display of parts according to content type. One or more -type switches part will only select the first match from a multipart/alternative, even if there is more than one subpart that matches (one of) the given content type(s). Using either -part or -type switches alone will cause either switch to select the part(s) they match. Using them together will select only the part(s) matched by both (sets of) switches. In other words, the result is the intersection, and not the union, of their sepa‐ rate match results. A content specification consists of a content type and a subtype. The initial list of “stan‐ dard” content types and subtypes can be found in RFC 2046. A list of commonly used contents is briefly reproduced here: Type Subtypes ---- -------- text plain, enriched multipart mixed, alternative, digest, parallel message rfc822, partial, external-body application octet-stream, postscript image jpeg, gif, png audio basic video mpeg A legal MIME message must contain a subtype specification. To specify a content, regardless of its subtype, just use the name of the content, e.g., “au‐ dio”. To specify a specific subtype, separate the two with a slash, e.g., “audio/basic”. Note that regardless of the values given to the -type switch, a multipart content (of any subtype listed above) is always acted upon. Further note that if the -type switch is used, and it is desirable to act on a message/external-body content, then the -type switch must be used twice: once for message/external-body and once for the content externally referenced. In the absence of -prefer, mhshow will select the \"best\" displayable subpart from multi‐ part/alternative content. The -prefer switch can be used (one or more times, in order of as‐ cending preference) to let MH know which content types from a multipart/alternative MIME part are preferred by the user, in order to override the default selection for display. For exam‐ ple, mail is often sent containing both plaintext and HTML-formatted versions of the same content, and the HTML version is usually indicated to be the \"best\" format for viewing. Us‐ ing “-prefer text/plain” will cause the plaintext version to be displayed if possible, but still allow display of the HTML part if there is no plaintext subpart available. Using “-prefer text/plain -prefer image/png” would add a preference for PNG images, which might or might not ever appear in the same multipart/alternative section with text/plain. Implementa‐ tion note: RFC 2046 requires that the subparts of a multipart/alternative be ordered accord‐ ing to \"faithfulness to the original content\", and MH by default selects the subpart ranked most \"faithful\" by that ordering. The -prefer switch reorders the alternative parts (only internally, never changing the message file) to move the user's preferred part(s) to the \"most faithful\" position. Thus, when viewed by mhlist, the ordering of multipart/alternative parts will appear to change when invoked with or without various -prefer switches. Since the last of multiple -prefer options \"wins\", a -prefer on the command line will override any in a profile entry. The -noprefer switch will cancel any previous -prefer switches." } ], "examples": [], "see_also": [ { "name": "iconv", "section": "3", "url": "https://www.chedong.com/phpMan.php/man/iconv/3/json" }, { "name": "mhbuild", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/mhbuild/1/json" }, { "name": "mhl", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/mhl/1/json" }, { "name": "mhlist", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/mhlist/1/json" }, { "name": "mhparam", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/mhparam/1/json" }, { "name": "mhstore", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/mhstore/1/json" }, { "name": "sendfiles", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/sendfiles/1/json" } ] }