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How to use this program

With the synopsis of the recode call, we stress the difference between using this program as a file filter, or recoding many files at once. The first parameter of any call states the recoding request, and this deserves a section on its own. Options are then presented, but somewhat grouped according to the related functionalities they control.

Synopsis of recode call

The general format of the program call is one of:

recode [option]... [charset | request [file]... ]

Some calls are used only to obtain lists produced by recode itself, without actually recoding any file. They are recognised through the usage of listing options, and these options decide what meaning should be given to an optional charset parameter. See section Asking for various lists.

In other calls, the first parameter (request) always explains which transformations are expected on the files. There are many variations to the aspect of this parameter. We will discuss more complex situations later (see section The request parameter), but for many simple cases, this parameter merely looks like(3):

before..after

where before and after each gives the name of a charset. Each file will be read assuming it is coded with charset before, it will be recoded over itself so to use the charset after. If there is no file on the recode command, the program rather acts as a Unix filter and transforms standard input onto standard output.

The capability of recoding many files at once is very convenient. For example, one could easily prepare a distribution from Latin-1 to MSDOS, this way:

mkdir package
cp -p Makefile *.[ch] package
recode Latin-1..MSDOS package/*
zoo ah package.zoo package/*
rm -rf package

(In this example, the non-mandatory `-p' option to cp is for preserving timestamps, and the zoo program is an archiver from Rahul Dhesi which once was quite popular.)

The filter operation is especially useful when the input files should not be altered. Let us make an example to illustrate this point. Suppose that someone has a file named `datum.txt', which is almost a TeX file, except that diacriticised characters are written using Latin-1. To complete the recoding of the diacriticised characters only and produce a file `datum.tex', without destroying the original, one could do:

cp -p datum.txt datum.tex
recode -d l1..tex datum.tex

However, using recode as a filter will achieve the same goal more neatly:

recode -d l1..tex <datum.txt >datum.tex

This example also shows that l1 could be used instead of Latin-1; charset names often have such aliases.

The request parameter

In the case where the request is merely written as before..after, then before and after specify the start charset and the goal charset for the recoding.

For recode, charset names may contain any character, besides a comma, a forward slash, or two periods in a row. But in practice, charset names are currently limited to alphabetic letters (upper or lower case), digits, hyphens, underlines, periods, colons or round parentheses.

The complete syntax for allowable request allows for unusual things, which might surprise at first. (Do not pay too much attention to these facilities on a first reading.) For example, request may also contain intermediary charsets, like in:

before..interim1..interim2..after

meaning that recode should internally produce the interim1 charset from the start charset, then work out of this interim1 charset to internally produce interim2, and from there towards the goal charset. In fact, recode internally combines recipes and automatically uses interim charsets, when there is no direct recipe for transforming before into after. But there might be many ways to do it. When many routes are possible, the above chaining syntax may be used to more precisely force the program towards a particular route, which it might not have naturally selected otherwise. On the other hand, because recode tries to choose good routes, chaining is only needed to achieve some rare, unusual effects.

Moreover, many such requests (sub-requests, more precisely) may be separated with commas (but no spaces at all), indicating a sequence of recodings, where the output of one has to serve as the input of the following one. For example, the two following requests are equivalent:

before..interim1..interim2..after
before..interim1,interim1..interim2,interim2..after

In this example, the charset input for any recoding sub-request is identical to the charset output by the preceding sub-request. But it does not have to be in the general case. One might wonder what would be the meaning of declaring the charset input for a recoding sub-request of being of different nature than the charset output by a preceding sub-request, when recodings are chained in this way. These strange usages might have a meaning and be useful for the recode expert, but they are quite uncommon in practice.

More useful is the distinction between the concept of charset, and the concept of surfaces. An encoded charset is represented by:

pure-charset/surface1/surface2...

using slashes to introduce surfaces, if any. The order of application of surfaces is usually important, they cannot be freely commuted. In the given example, surface1 is first applied over the pure-charset, then surface2 is applied over the result. Given this request:

before/surface1/surface2..after/surface3

the recode program will understand that the input files should have surface2 removed first (because it was applied last), then surface1 should be removed. The next step will be to translate the codes from charset before to charset after, prior to applying surface3 over the result.

Some charsets have one or more implied surfaces. In this case, the implied surfaces are automatically handled merely by naming the charset, without any explicit surface to qualify it. Let's take an example to illustrate this feature. The request `pc..l1' will indeed decode MS-DOS end of lines prior to converting IBM-PC codes to Latin-1, because `pc' is the name of a charset(4) which has CR-LF for its usual surface. The request `pc/..l1' will not decode end of lines, since the slash introduces surfaces, and even if the surface list is empty, it effectively defeats the automatic removal of surfaces for this charset. So, empty surfaces are useful, indeed!

Both charsets and surfaces may have predefined alternate names, or aliases. However, and this is rather important to understand, implied surfaces are attached to individual aliases rather than on genuine charsets. Consequently, the official charset name and all of its aliases do not necessarily share the same implied surfaces. The charset and all its aliases may each have its own different set of implied surfaces.

Charset names, surface names, or their aliases may always be abbreviated to any unambiguous prefix. Internally in recode, disambiguating tables are kept separate for charset names and surface names.

While recognising a charset name or a surface name (or aliases thereof), recode ignores all characters besides letters and digits, so for example, the hyphens and underlines being part of an official charset name may safely be omitted (no need to un-confuse them!). There is also no distinction between upper and lower case for charset or surface names.

One of the before or after keywords may be omitted. If the double dot separator is omitted too, then the charset is interpreted as the before charset.(5)

When a charset name is omitted or left empty, the value of the DEFAULT_CHARSET variable in the environment is used instead. If this variable is not defined, the recode library uses an usual charset which is installation dependent. When this variable is defined but has an empty value, charset names may just not be omitted. Unless overriden when recode was installed, this usual charset is Latin-1 for Unix systems or IBM-PC for MS-DOS machines.

If the charset name is omitted but followed by surfaces, the surfaces then qualify the usual or default charset. For example, the request `../x' is sufficient for applying an hexadecimal surface to the input text(6).

The allowable values for before or after charsets, and various surfaces, are described in the remainder of this document.

Asking for various lists

Many options control listing output generated by recode itself, they are not meant to accompany actual file recodings. These options are:

`--version'
The program merely prints its version numbers on standard output, and exits without doing anything else.
`--help'
The program merely prints a page of help on standard output, and exits without doing any recoding.
`-C'
`--copyright'
Given this option, all other parameters and options are ignored. The program prints briefly the copyright and copying conditions. See the file `COPYING' in the distribution for full statement of the Copyright and copying conditions.
`-h[language/][name]'
`--header[=[language/][name]]'
Instead of recoding files, recode writes a language source file on standard output and exits. This source is meant to be included in a regular program written in the same programming language: its purpose is to declare and initialise an array, named name, which represents the requested recoding. The only acceptable values for language are `c' or `perl', and may may be abbreviated. If language is not specified, `c' is assumed. If name is not specified, then it defaults to `before_after'. Strings before and after are cleaned before being used according to the syntax of language. Even if recode tries its best, this option does not always succeed in producing the requested source table. It will however, provided the recoding can be internally represented by only one step after the optimisation phase, and if this merged step conveys a one-to-one or a one-to-many explicit table. Also, when attempting to produce sources tables, recode relaxes its checking a tiny bit: it ignores the algorithmic part of some tabular recodings, it also avoids the processing of implied surfaces. But this is all fairly technical. Better try and see! Beware that other options might affect the produced source tables, these are: -d, -g and, particularly, -s.
`-k pairs'
`--known=pairs'
This particular option is meant to help identifying an unknown charset, using as hints some already identified characters of the charset. Some examples will help introducing the idea. Let's presume here that recode is run on Unix, where Latin-1 is the usual charset, and that DEFAULT_CHARSET is unset in the environment. Suppose you have guessed that code 130 (decimal) of the unknown charset represents a lower case `e' with an acute accent. That is to say that this code should map to code 233 (decimal) in the usual charset. By executing:
recode -k 130:233
you should obtain a listing similar to:
AtariST atarist
CWI cphu cwi cwi2
IBM437 437 cp437 ibm437
IBM850 850 cp850 ibm850
IBM851 851 cp851 ibm851
IBM852 852 cp852 ibm852
IBM857 857 cp857 ibm857
IBM860 860 cp860 ibm860
IBM861 861 cp861 cpis ibm861
IBM863 863 cp863 ibm863
IBM865 865 cp865 ibm865
You can give more than one clue at once, to restrict the list further. Suppose you have also guessed that code 211 of the unknown charset represents an upper case `E' with diaeresis, that is, code 203 in the usual charset. By requesting:
recode -k 130:233,211:203
you should obtain:
IBM850 850 cp850 ibm850
IBM852 852 cp852 ibm852
IBM857 857 cp857 ibm857
The usual charset may be overridden by specifying one non-option argument. For example, to request the list of charsets for which code 130 maps to code 142 for the Macintosh, you may ask:
recode -k 130:142 mac
and get:
AtariST atarist
CWI cphu cwi cwi2
IBM437 437 cp437 ibm437
IBM850 850 cp850 ibm850
IBM851 851 cp851 ibm851
IBM852 852 cp852 ibm852
IBM857 857 cp857 ibm857
IBM860 860 cp860 ibm860
IBM861 861 cp861 cpis ibm861
IBM863 863 cp863 ibm863
IBM865 865 cp865 ibm865
which, of course, is identical to the result of the first example, since the code 142 for the Macintosh is a small `e' with acute. More formally, option `-k' lists all possible before charsets for the after charset given as the sole non-option argument to recode, but subject to restrictions given in pairs. If there is no non-option argument, the after charset is taken to be the default charset for this recode. The restrictions are given as a comma separated list of pairs, each pair consisting of two numbers separated by a colon. The numbers are taken as decimal when the initial digit is between `1' and `9'; `0x' starts an hexadecimal number, or else `0' starts an octal number. The first number is a code in any before charset, while the second number is a code in the specified after charset. If the first number would not be transformed into the second number by recoding from some before charset to the after charset, then this before charset is rejected. A before charset is listed only if it is not rejected by any pair. The program will only test those before charsets having a tabular style internal description (see section Tabular sources (RFC 1345)), so should be the selected after charset. The produced list is in fact a subset of the list produced by the option `-l'. As for option `-l', the non-option argument is interpreted as a charset name, possibly abbreviated to any non ambiguous prefix.
`-l[format]'
`--list[=format]'
This option asks for information about all charsets, or about one particular charset. No file will be recoded. If there is no non-option arguments, recode ignores the format value of the option, it writes a sorted list of charset names on standard output, one per line. When a charset name have aliases or synonyms, they follow the true charset name on its line, sorted from left to right. Each charset or alias is followed by its implied surfaces, if any. This list is over two hundred lines. It is best used with `grep -i', as in:
recode -l | grep -i greek
There might be one non-option argument, in which case it is interpreted as a charset name, possibly abbreviated to any non ambiguous prefix. This particular usage of the -l option is obeyed only for charsets having a tabular style internal description (see section Tabular sources (RFC 1345)). Even if most charsets have this property, some do not, then option -l cannot be used to detail these particular charsets. For knowing if a particular charset can be listed this way, you should merely try and see if this works. The format value of the option is a keyword from the following list. Keywords may be abbreviated by dropping suffix letters, and even reduced to the first letter only:
`decimal'
This format asks for the production on standard output of a concise tabular display of the charset, in which character code values are expressed in decimal.
`octal'
This format uses octal instead of decimal in the concise tabular display of the charset.
`hexadecimal'
This format uses hexadecimal instead of decimal in the concise tabular display of the charset.
`full'
This format requests an extensive display of the charset on standard output, using one line per character showing its decimal, hexadecimal, octal and UCS-2 code values, and also a descriptive comment which should be the 10646 name for the character. The descriptive comment is given in English and ASCII, yet if the English description is not available but a French one is, then the French description is given instead, using Latin-1. However, if the LANGUAGE or LANG environment variable begins with the letters `fr', then listing preference goes to French when both descriptions are available.
When option -l is used together with a charset argument, the format defaults to decimal.
`-T'
`--find-subsets'
This option is a maintainer tool for evaluating the redundancy of those charsets, in recode, which are internally represented by an UCS-2 data table. After the listing has been produced, the program exits without doing any recoding. The output of is meant to be sorted, like this: `recode -T | sort'. The option triggers recode into comparing all pairs of charsets, seeking those which are subsets of others. The concept and results are better explained through a few examples. Consider these three sample lines from -T output:
[  0] IBM891 == IBM903
[  1] IBM1004 < CP1252
[ 12] INVARIANT < CSA_Z243.4-1985-1
The first line means that IBM891 and IBM903 are completely identical as far as recode is concerned, so one is fully redundant to the other. The second line says that IBM1004 is wholly contained within CP1252, yet there is a single character which is in CP1252 without being in IBM1004. The third line says that INVARIANT is wholly contained within CSA_Z243.4-1985-1, but twelve characters are in CSA_Z243.4-1985-1 without being in INVARIANT. The whole output might most probably be reduced and made more significant through a transitivity study.

Controlling how files are recoded

The following options have the purpose of giving the user some fine grain control over the recoding operation themselves.

`-c'
`--colons'
With Texte Easy French conventions, use the column : instead of the double-quote " for marking diaeresis. See section Easy French conventions.
`-g'
`--graphics'
This option is only meaningful while getting out of the IBM-PC charset. In this charset, characters 176 to 223 are used for constructing rulers and boxes, using simple or double horizontal or vertical lines. This option forces the automatic selection of ASCII characters for approximating these rulers and boxes, at cost of making the transformation irreversible. Option -g implies -f.
`-t'
`--touch'
The touch option is meaningful only when files are recoded over themselves. Without it, the time-stamps associated with files are preserved, to reflect the fact that changing the code of a file does not really alter its informational contents. When the user wants the recoded files to be time-stamped at the recoding time, this option inhibits the automatic protection of the time-stamps.
`-v'
`--verbose'
Before doing any recoding, the program will first print on `stderr' the list of all intermediate charsets planned for recoding, starting with the before charset and ending with the after charset. It also prints an indication of the recoding quality, as one of the word `reversible', `one to one', `one to many', `many to one' or `many to many'. This information will appear once or twice. It is shown a second time only when the optimisation and step merging phase succeeds in replacing many single steps by a new one. This option also has a second effect. The program will print on `stderr' one message per file recoded, so to keep the user informed of the progress of its command. An easy way to know beforehand the sequence or quality of a recoding is by using the command such as:
recode -v before..after < /dev/null
also using the fact that, in recode, an empty input file produces an empty output file.
`-x charset'
`--ignore=charset'
This option tells the program to ignore any recoding path through the specified charset, so disabling any single step using this charset as a start or end point. This may be used when the user wants to force recode into using an alternate recoding path (yet using chained requests offers a finer control, see section The request parameter). charset may be abbreviated to any unambiguous prefix.

Reversibility issues

The following options are somewhat related to reversibility issues:

`-f'
`--force'
With this option, irreversible or otherwise erroneous recodings are run to completion, and recode does not exit with a non-zero status if it would be only because irreversibility matters. See section Reversibility issues. Without this option, recode tries to protect you against recoding a file irreversibly over itself(7). Whenever an irreversible recoding is met, or any other recoding error, recode produces a warning on standard error. The current input file does not get replaced by its recoded version, and recode then proceeds with the recoding of the next file. When the program is merely used as a filter, standard output will have received a partially recoded copy of standard input, up to the first error point. After all recodings have been done or attempted, and if some recoding has been aborted, recode exits with a non-zero status. In releases of recode prior to version 3.5, this option was always selected, so it was rather meaningless. Nevertheless, users were invited to start using `-f' right away in scripts calling recode whenever convenient, in preparation for the current behaviour.
`-q'
`--quiet'
`--silent'
This option has the sole purpose of inhibiting warning messages about irreversible recodings, and other such diagnostics. It has no other effect, in particular, it does not prevent recodings to be aborted or recode to return a non-zero exit status when irreversible recodings are met. This option is set automatically for the children processes, when recode splits itself in many collaborating copies. Doing so, the diagnostic is issued only once by the parent. See option -p.
`-s'
`--strict'
By using this option, the user requests that recode be very strict while recoding a file, merely losing in the transformation any character which is not explicitly mapped from a charset to another. Such a loss is not reversible and so, will bring recode to fail, unless the option -f is also given as a kind of counter-measure. Using -s without -f might render the recode program very susceptible to the slighest file abnormalities. Despite it might be irritating to some users, such paranoia is sometimes wanted and useful.

Even if recode tries hard at keeping the recodings reversible, you should not develop an unconditional confidence in its ability to do so. You ought to keep only reasonable expectations about reverse recodings. In particular, consider:

Unless option -s is used, recode automatically tries to fill mappings with invented correspondences, often making them fully reversible. This filling is not made at random. The algorithm tries to stick to the identity mapping and, when this is not possible, it prefers generating many small permutation cycles, each involving only a few codes.

For example, here is how IBM-PC code 186 gets translated to control-U in Latin-1. Control-U is 21. Code 21 is the IBM-PC section sign, which is 167 in Latin-1. recode cannot reciprocate 167 to 21, because 167 is the masculine ordinal indicator within IBM-PC, which is 186 in Latin-1. Code 186 within IBM-PC has no Latin-1 equivalent; by assigning it back to 21, recode closes this short permutation loop.

As a consequence of this map filling, recode may sometimes produce funny characters. They may look annoying, they are nevertheless helpful when one changes his (her) mind and wants to revert to the prior recoding. If you cannot stand these, use option -s, which asks for a very strict recoding.

This map filling sometimes has a few surprising consequences, which some users wrongly interpreted as bugs. Here are two examples.

  1. In some cases, recode seems to copy a file without recoding it. But in fact, it does. Consider you requested:
    recode l1..us < File-Latin1 > File-ASCII
    cmp File-Latin1 File-ASCII
    
    then cmp will not report any difference. This is quite normal. Latin-1 gets correctly recoded to ASCII for charsets commonalities (which are the first 128 characters, in this case). The remaining last 128 Latin-1 characters have no ASCII correspondent. Instead of losing them, recode elects to map them to unspecified characters of ASCII, so making the recoding reversible. The simplest way of achieving this is merely to keep those last 128 characters unchanged. The overall effect is copying the file verbatim. If you feel this behaviour is too generous and if you do not wish to care about reversibility, simply use option -s. By doing so, recode will strictly map only those Latin-1 characters which have an ASCII equivalent, and will merely drop those which do not. Then, there is more chance that you will observe a difference between the input and the output file.
  2. Recoding the wrong way could sometimes give the false impression that recoding has almost been done properly. Consider you request:
    recode 437..l1 < File-Latin1 > Temp1
    recode 437..l1 < Temp1 > Temp2
    
    so declaring wrongly `File-Latin1' to be an IBM-PC file, and recoding to Latin1. This is surely ill defined and not meaningful. Yet, if you repeat this step a second time, you might notice that many (not all) characters in `Temp2' are identical to those in `File-Latin1'. A few people try to discover how recode works by experimenting a little at random, rather than reading and understanding the documentation; such results are surely confusing, as they provide a feel to those people that they understood something. Reversible codings have this property that, if applied several times in the same direction, they will eventually bring any character back to its original value. Since recode seeks small permutation cycles when creating reversible codings, besides characters unchanged by the recoding, most permutation cycles will be of length 2, and fewer of length 3, etc. So, it is just expectable that applying the recoding twice in the same direction will recover most characters, but will fail to recover those participating in permutation cycles of length 3. On the other end, recoding six times in the same direction would recover all characters in cycles of length 1, 2, 3 or 6.

Selecting sequencing methods

This program uses a few techniques when it is discovered that many passes are needed to comply with the request. For example, suppose that four elementary steps were selected at recoding path optimisation time. Then recode will split itself into four different interconnected tasks, logically equivalent to:

step1 <input | step2 | step3 | step4 >output

The splitting into subtasks is often done using Unix pipes. But the splitting may also be completely avoided, and rather simulated by using memory buffer, or intermediate files. The various `--sequence=strategy' options gives you control over the flow methods, by replacing strategy with `memory', `pipe' or `files'. So, these options may be used to override the default behaviour, which is also explained below.

`--sequence=memory'
When the recoding requires a combination of two or more elementary recoding steps, this option forces many passes over the data, using in-memory buffers to hold all intermediary results.
`-i'
`--sequence=files'
When the recoding requires a combination of two or more elementary recoding steps, this option forces many passes over the data, using intermediate files between passes. This is the default behaviour when files are recoded over themselves. If this option is selected in filter mode, that is, when the program reads standard input and writes standard output, it might take longer for programs further down the pipe chain to start receiving some recoded data.
`-p'
`--sequence=pipe'
When the recoding requires a combination of two or more elementary recoding steps, this option forces the program to fork itself into a few copies interconnected with pipes, using the pipe(2) system call. All copies of the program operate in parallel. This is the default behaviour in filter mode. If this option is used when files are recoded over themselves, this should also save disk space because some temporary files might not be needed, at cost of more system overhead. If, at installation time, the pipe(2) call is said to be unavailable, selecting option -p is equivalent to selecting option -i.

Using mixed charset input

In real life and practice, textual files are often made up of many charsets at once. Some parts of the file encode one charset, while other parts encode another charset, and so forth. Usually, a file does not toggle between more than two or three charsets. The means to distinguish which charsets are encoded at various places is not always easy. The recode program is able to handle only a few simple cases of mixed input.

The default recode behaviour is to expect pure charset files, to be recoded as other pure charset files. However, the following options allow for a few precise kinds of mixed charset files.

`-d'
`--diacritics'
While converting to or from one of HTML or LaTeX charset, limit conversion to some subset of all characters. For HTML, limit conversion to the subset of all non-ASCII characters. For LaTeX, limit conversion to the subset of all non-English letters. This is particularly useful, for example, when people create what would be valid HTML, TeX or LaTeX files, if only they were using provided sequences for applying diacritics instead of using the diacriticised characters directly from the underlying character set. While converting to HTML or LaTeX charset, this option assumes that characters not in the said subset are properly coded or protected already, recode then transmit them literally. While converting the other way, this option prevents translating back coded or protected versions of characters not in the said subset. See section World Wide Web representations. See section LaTeX macro calls.
`-S[language]'
`--source[=language]'
The bulk of the input file is expected to be written in ASCII, except for parts, like comments and string constants, which are written using another charset than ASCII. When language is `c', the recoding will proceed only with the contents of comments or strings, while everything else will be copied without recoding. When language is `po', the recoding will proceed only within translator comments (those having whitespace immediately following the initial `#') and with the contents of msgstr strings. For the above things to work, the non-ASCII encoding of the comment or string should be such that an ASCII scan will successfully find where the comment or string ends. Even if ASCII is the usual charset for writing programs, some compilers are able to directly read other charsets, like UTF-8 say. There is currently no provision in recode for reading mixed charset sources which are not based on ASCII. It is probable that the need for mixed recoding is not as pressing in such cases. For example, after one does:
recode -Spo pc/..u8 < input.po > output.po
file `output.po' holds a copy of `input.po' in which translator comments and the contents of msgstr strings only have been recoded from the IBM-PC charset to pure UTF-8, without attempting conversion of end-of-lines. Machine generated comments and original msgid strings are not to be touched by this recoding. If language is not specified, `c' is assumed.

Using recode within Emacs

The fact recode is a filter makes it quite easy to use from within GNU Emacs. For example, recoding the whole buffer from the IBM-PC charset to current charset (Latin-1 on Unix) is easily done with:

C-x h C-u M-| recode ibmpc RET

The `C-x h' selects the whole buffer, and `C-u M-|' filters and replaces the current region through the given shell command. Here is another example, binding the keys `C-c T' to the recoding of the current region from Easy French to Latin-1 (on Unix) and the key `C-u C-c T' from Latin-1 (on Unix) to Easy French:

(global-set-key "\C-cT" 'recode-texte)

(defun recode-texte (flag)
  (interactive "P")
  (shell-command-on-region
   (region-beginning) (region-end)
   (concat "recode " (if flag "..txte" "txte")) t)
  (exchange-point-and-mark))


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