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NAME
io - Standard I/O Server Interface Functions
DESCRIPTION
This module provides an interface to standard Erlang I/O servers. The output functions all
return ok if they are successful, or exit if they are not.
In the following description, all functions have an optional parameter IoDevice. If
included, it must be the pid of a process which handles the IO protocols. Normally, it is
the IoDevice returned by file:open/2.
For a description of the IO protocols refer to the STDLIB User's Guide.
Warning:
As of R13A, data supplied to the put_chars function should be in the unicode:chardata()
format. This means that programs supplying binaries to this function need to convert them
to UTF-8 before trying to output the data on an IO device.
If an IO device is set in binary mode, the functions get_chars and get_line may return
binaries instead of lists. The binaries will, as of R13A, be encoded in UTF-8.
To work with binaries in ISO-latin-1 encoding, use the file module instead.
For conversion functions between character encodings, see the unicode module.
DATA TYPES
device() = atom() | pid()
An IO device. Either standard_io, standard_error, a registered name, or a pid
handling IO protocols (returned from file:open/2).
opt_pair() = {binary, boolean()}
| {echo, boolean()}
| {expand_fun, expand_fun()}
| {encoding, encoding()}
expand_fun() =
fun((term()) -> {yes | no, string(), [string(), ...]})
encoding() = latin1
| unicode
| utf8
| utf16
| utf32
| {utf16, big | little}
| {utf32, big | little}
setopt() = binary | list | opt_pair()
format() = atom() | string() | binary()
location() = erl_scan:location()
prompt() = atom() | unicode:chardata()
server_no_data() = {error, ErrorDescription :: term()} | eof
What the I/O-server sends when there is no data.
EXPORTS
columns() -> {ok, integer() >= 1} | {error, enotsup}
columns(IoDevice) -> {ok, integer() >= 1} | {error, enotsup}
Types:
IoDevice = device()
Retrieves the number of columns of the IoDevice (i.e. the width of a terminal). The
function only succeeds for terminal devices, for all other IO devices the function
returns {error, enotsup}
put_chars(CharData) -> ok
put_chars(IoDevice, CharData) -> ok
Types:
IoDevice = device()
CharData = unicode:chardata()
Writes the characters of CharData to the I/O server (IoDevice).
nl() -> ok
nl(IoDevice) -> ok
Types:
IoDevice = device()
Writes new line to the standard output (IoDevice).
get_chars(Prompt, Count) -> Data | server_no_data()
get_chars(IoDevice, Prompt, Count) -> Data | server_no_data()
Types:
IoDevice = device()
Prompt = prompt()
Count = integer() >= 0
Data = string() | unicode:unicode_binary()
server_no_data() = {error, ErrorDescription :: term()} | eof
Reads Count characters from standard input (IoDevice), prompting it with Prompt. It
returns:
Data:
The input characters. If the IO device supports Unicode, the data may represent
codepoints larger than 255 (the latin1 range). If the I/O server is set to
deliver binaries, they will be encoded in UTF-8 (regardless of if the IO device
actually supports Unicode or not).
eof:
End of file was encountered.
{error, ErrorDescription}:
Other (rare) error condition, for instance {error, estale} if reading from an
NFS file system.
get_line(Prompt) -> Data | server_no_data()
get_line(IoDevice, Prompt) -> Data | server_no_data()
Types:
IoDevice = device()
Prompt = prompt()
Data = string() | unicode:unicode_binary()
server_no_data() = {error, ErrorDescription :: term()} | eof
Reads a line from the standard input (IoDevice), prompting it with Prompt. It
returns:
Data:
The characters in the line terminated by a LF (or end of file). If the IO
device supports Unicode, the data may represent codepoints larger than 255 (the
latin1 range). If the I/O server is set to deliver binaries, they will be
encoded in UTF-8 (regardless of if the IO device actually supports Unicode or
not).
eof:
End of file was encountered.
{error, ErrorDescription}:
Other (rare) error condition, for instance {error, estale} if reading from an
NFS file system.
getopts() -> [opt_pair()]
getopts(IoDevice) -> [opt_pair()]
Types:
IoDevice = device()
This function requests all available options and their current values for a
specific IO device. Example:
1> {ok,F} = file:open("/dev/null",[read]).
{ok,<0.42.0>}
2> io:getopts(F).
[{binary,false},{encoding,latin1}]
Here the file I/O-server returns all available options for a file, which are the
expected ones, encoding and binary. The standard shell however has some more
options:
3> io:getopts().
[{expand_fun,#Fun<group.0.120017273>},
{echo,true},
{binary,false},
{encoding,unicode}]
This example is, as can be seen, run in an environment where the terminal supports
Unicode input and output.
printable_range() -> unicode | latin1
Return the user requested range of printable Unicode characters.
The user can request a range of characters that are to be considered printable in
heuristic detection of strings by the shell and by the formatting functions. This
is done by supplying +pc <range> when starting Erlang.
Currently the only valid values for <range> are latin1 and unicode. latin1 means
that only code points below 256 (with the exception of control characters etc) will
be considered printable. unicode means that all printable characters in all unicode
character ranges are considered printable by the io functions.
By default, Erlang is started so that only the latin1 range of characters will
indicate that a list of integers is a string.
The simplest way to utilize the setting is to call io_lib:printable_list/1, which
will use the return value of this function to decide if a list is a string of
printable characters or not.
Note:
In the future, this function may return more values and ranges. It is recommended
to use the io_lib:printable_list/1 function to avoid compatibility problems.
setopts(Opts) -> ok | {error, Reason}
setopts(IoDevice, Opts) -> ok | {error, Reason}
Types:
IoDevice = device()
Opts = [setopt()]
Reason = term()
Set options for the standard IO device (IoDevice).
Possible options and values vary depending on the actual IO device. For a list of
supported options and their current values on a specific IO device, use the
getopts/1 function.
The options and values supported by the current OTP IO devices are:
binary, list or {binary, boolean()}:
If set in binary mode (binary or {binary, true}), the I/O server sends binary
data (encoded in UTF-8) as answers to the get_line, get_chars and, if possible,
get_until requests (see the I/O protocol description in STDLIB User's Guide for
details). The immediate effect is that get_chars/2,3 and get_line/1,2 return
UTF-8 binaries instead of lists of chars for the affected IO device.
By default, all IO devices in OTP are set in list mode, but the I/O functions
can handle any of these modes and so should other, user written, modules
behaving as clients to I/O-servers.
This option is supported by the standard shell (group.erl), the 'oldshell'
(user.erl) and the file I/O servers.
{echo, boolean()}:
Denotes if the terminal should echo input. Only supported for the standard
shell I/O-server (group.erl)
{expand_fun, expand_fun()}:
Provide a function for tab-completion (expansion) like the Erlang shell. This
function is called when the user presses the TAB key. The expansion is active
when calling line-reading functions such as get_line/1,2.
The function is called with the current line, upto the cursor, as a reversed
string. It should return a three-tuple: {yes|no, string(), [string(), ...]}.
The first element gives a beep if no, otherwise the expansion is silent, the
second is a string that will be entered at the cursor position, and the third
is a list of possible expansions. If this list is non-empty, the list will be
printed and the current input line will be written once again.
Trivial example (beep on anything except empty line, which is expanded to
"quit"):
fun("") -> {yes, "quit", []};
(_) -> {no, "", ["quit"]} end
This option is supported by the standard shell only (group.erl).
{encoding, latin1 | unicode}:
Specifies how characters are input or output from or to the actual IO device,
implying that i.e. a terminal is set to handle Unicode input and output or a
file is set to handle UTF-8 data encoding.
The option does not affect how data is returned from the I/O functions or how
it is sent in the I/O-protocol, it only affects how the IO device is to handle
Unicode characters towards the "physical" device.
The standard shell will be set for either Unicode or latin1 encoding when the
system is started. The actual encoding is set with the help of the LANG or
LC_CTYPE environment variables on Unix-like system or by other means on other
systems. The bottom line is that the user can input Unicode characters and the
IO device will be in {encoding, unicode} mode if the IO device supports it. The
mode can be changed, if the assumption of the runtime system is wrong, by
setting this option.
The IO device used when Erlang is started with the "-oldshell" or "-noshell"
flags is by default set to latin1 encoding, meaning that any characters beyond
codepoint 255 will be escaped and that input is expected to be plain 8-bit ISO-
latin-1. If the encoding is changed to Unicode, input and output from the
standard file descriptors will be in UTF-8 (regardless of operating system).
Files can also be set in {encoding, unicode}, meaning that data is written and
read as UTF-8. More encodings are possible for files, see below.
{encoding, unicode | latin1} is supported by both the standard shell (group.erl
including werl on Windows(R)), the 'oldshell' (user.erl) and the file I/O
servers.
{encoding, utf8 | utf16 | utf32 | {utf16,big} | {utf16,little} | {utf32,big} |
{utf32,little}}:
For disk files, the encoding can be set to various UTF variants. This will have
the effect that data is expected to be read as the specified encoding from the
file and the data will be written in the specified encoding to the disk file.
{encoding, utf8} will have the same effect as {encoding, unicode} on files.
The extended encodings are only supported on disk files (opened by the
file:open/2 function)
write(Term) -> ok
write(IoDevice, Term) -> ok
Types:
IoDevice = device()
Term = term()
Writes the term Term to the standard output (IoDevice).
read(Prompt) -> Result
read(IoDevice, Prompt) -> Result
Types:
IoDevice = device()
Prompt = prompt()
Result = {ok, Term :: term()}
| server_no_data()
| {error, ErrorInfo}
ErrorInfo = erl_scan:error_info() | erl_parse:error_info()
server_no_data() = {error, ErrorDescription :: term()} | eof
Reads a term Term from the standard input (IoDevice), prompting it with Prompt. It
returns:
{ok, Term}:
The parsing was successful.
eof:
End of file was encountered.
{error, ErrorInfo}:
The parsing failed.
{error, ErrorDescription}:
Other (rare) error condition, for instance {error, estale} if reading from an
NFS file system.
read(IoDevice, Prompt, StartLocation) -> Result
read(IoDevice, Prompt, StartLocation, Options) -> Result
Types:
IoDevice = device()
Prompt = prompt()
StartLocation = location()
Options = erl_scan:options()
Result = {ok, Term :: term(), EndLocation :: location()}
| {eof, EndLocation :: location()}
| server_no_data()
| {error, ErrorInfo, ErrorLocation :: location()}
ErrorInfo = erl_scan:error_info() | erl_parse:error_info()
server_no_data() = {error, ErrorDescription :: term()} | eof
Reads a term Term from IoDevice, prompting it with Prompt. Reading starts at
location StartLocation. The argument Options is passed on as the Options argument
of the erl_scan:tokens/4 function. It returns:
{ok, Term, EndLocation}:
The parsing was successful.
{eof, EndLocation}:
End of file was encountered.
{error, ErrorInfo, ErrorLocation}:
The parsing failed.
{error, ErrorDescription}:
Other (rare) error condition, for instance {error, estale} if reading from an
NFS file system.
fwrite(Format) -> ok
fwrite(Format, Data) -> ok
fwrite(IoDevice, Format, Data) -> ok
format(Format) -> ok
format(Format, Data) -> ok
format(IoDevice, Format, Data) -> ok
Types:
IoDevice = device()
Format = format()
Data = [term()]
Writes the items in Data ([]) on the standard output (IoDevice) in accordance with
Format. Format contains plain characters which are copied to the output device, and
control sequences for formatting, see below. If Format is an atom or a binary, it
is first converted to a list with the aid of atom_to_list/1 or binary_to_list/1.
1> io:fwrite("Hello world!~n", []).
Hello world!
ok
The general format of a control sequence is ~F.P.PadModC. The character C
determines the type of control sequence to be used, F and P are optional numeric
arguments. If F, P, or Pad is *, the next argument in Data is used as the numeric
value of F or P.
F is the field width of the printed argument. A negative value means that the
argument will be left justified within the field, otherwise it will be right
justified. If no field width is specified, the required print width will be used.
If the field width specified is too small, then the whole field will be filled with
* characters.
P is the precision of the printed argument. A default value is used if no precision
is specified. The interpretation of precision depends on the control sequences.
Unless otherwise specified, the argument within is used to determine print width.
Pad is the padding character. This is the character used to pad the printed
representation of the argument so that it conforms to the specified field width and
precision. Only one padding character can be specified and, whenever applicable, it
is used for both the field width and precision. The default padding character is '
' (space).
Mod is the control sequence modifier. It is either a single character (currently
only t, for Unicode translation, and l, for stopping p and P from detecting
printable characters, are supported) that changes the interpretation of Data.
The following control sequences are available:
~:
The character ~ is written.
c:
The argument is a number that will be interpreted as an ASCII code. The
precision is the number of times the character is printed and it defaults to
the field width, which in turn defaults to 1. The following example
illustrates:
1> io:fwrite("|~10.5c|~-10.5c|~5c|~n", [$a, $b, $c]).
| aaaaa|bbbbb |ccccc|
ok
If the Unicode translation modifier (t) is in effect, the integer argument can
be any number representing a valid Unicode codepoint, otherwise it should be an
integer less than or equal to 255, otherwise it is masked with 16#FF:
2> io:fwrite("~tc~n",[1024]).
\x{400}
ok
3> io:fwrite("~c~n",[1024]).
^@
ok
f:
The argument is a float which is written as [-]ddd.ddd, where the precision is
the number of digits after the decimal point. The default precision is 6 and it
cannot be less than 1.
e:
The argument is a float which is written as [-]d.ddde+-ddd, where the precision
is the number of digits written. The default precision is 6 and it cannot be
less than 2.
g:
The argument is a float which is written as f, if it is >= 0.1 and < 10000.0.
Otherwise, it is written in the e format. The precision is the number of
significant digits. It defaults to 6 and should not be less than 2. If the
absolute value of the float does not allow it to be written in the f format
with the desired number of significant digits, it is also written in the e
format.
s:
Prints the argument with the string syntax. The argument is, if no Unicode
translation modifier is present, an iolist(), a binary(), or an atom(). If the
Unicode translation modifier (t) is in effect, the argument is
unicode:chardata(), meaning that binaries are in UTF-8. The characters are
printed without quotes. The string is first truncated by the given precision
and then padded and justified to the given field width. The default precision
is the field width.
This format can be used for printing any object and truncating the output so it
fits a specified field:
1> io:fwrite("|~10w|~n", [{hey, hey, hey}]).
|**********|
ok
2> io:fwrite("|~10s|~n", [io_lib:write({hey, hey, hey})]).
|{hey,hey,h|
3> io:fwrite("|~-10.8s|~n", [io_lib:write({hey, hey, hey})]).
|{hey,hey |
ok
A list with integers larger than 255 is considered an error if the Unicode
translation modifier is not given:
4> io:fwrite("~ts~n",[[1024]]).
\x{400}
ok
5> io:fwrite("~s~n",[[1024]]).
** exception exit: {badarg,[{io,format,[<0.26.0>,"~s~n",[[1024]]]},
...
w:
Writes data with the standard syntax. This is used to output Erlang terms.
Atoms are printed within quotes if they contain embedded non-printable
characters, and floats are printed accurately as the shortest, correctly
rounded string.
p:
Writes the data with standard syntax in the same way as ~w, but breaks terms
whose printed representation is longer than one line into many lines and
indents each line sensibly. It also tries to detect lists of printable
characters and to output these as strings. The Unicode translation modifier is
used for determining what characters are printable. For example:
1> T = [{attributes,[[{id,age,1.50000},{mode,explicit},
{typename,"INTEGER"}], [{id,cho},{mode,explicit},{typename,'Cho'}]]},
{typename,'Person'},{tag,{'PRIVATE',3}},{mode,implicit}].
...
2> io:fwrite("~w~n", [T]).
[{attributes,[[{id,age,1.5},{mode,explicit},{typename,
[73,78,84,69,71,69,82]}],[{id,cho},{mode,explicit},{typena
me,'Cho'}]]},{typename,'Person'},{tag,{'PRIVATE',3}},{mode
,implicit}]
ok
3> io:fwrite("~62p~n", [T]).
[{attributes,[[{id,age,1.5},
{mode,explicit},
{typename,"INTEGER"}],
[{id,cho},{mode,explicit},{typename,'Cho'}]]},
{typename,'Person'},
{tag,{'PRIVATE',3}},
{mode,implicit}]
ok
The field width specifies the maximum line length. It defaults to 80. The
precision specifies the initial indentation of the term. It defaults to the
number of characters printed on this line in the same call to io:fwrite or
io:format. For example, using T above:
4> io:fwrite("Here T = ~62p~n", [T]).
Here T = [{attributes,[[{id,age,1.5},
{mode,explicit},
{typename,"INTEGER"}],
[{id,cho},
{mode,explicit},
{typename,'Cho'}]]},
{typename,'Person'},
{tag,{'PRIVATE',3}},
{mode,implicit}]
ok
When the modifier l is given no detection of printable character lists will
take place. For example:
5> S = [{a,"a"}, {b, "b"}].
6> io:fwrite("~15p~n", [S]).
[{a,"a"},
{b,"b"}]
ok
7> io:fwrite("~15lp~n", [S]).
[{a,[97]},
{b,[98]}]
ok
Binaries that look like UTF-8 encoded strings will be output with the string
syntax if the Unicode translation modifier is given:
9> io:fwrite("~p~n",[[1024]]).
[1024]
10> io:fwrite("~tp~n",[[1024]]).
"\x{400}"
11> io:fwrite("~tp~n", [<<128,128>>]).
<<128,128>>
12> io:fwrite("~tp~n", [<<208,128>>]).
<<"\x{400}"/utf8>>
ok
W:
Writes data in the same way as ~w, but takes an extra argument which is the
maximum depth to which terms are printed. Anything below this depth is replaced
with .... For example, using T above:
8> io:fwrite("~W~n", [T,9]).
[{attributes,[[{id,age,1.5},{mode,explicit},{typename,...}],
[{id,cho},{mode,...},{...}]]},{typename,'Person'},
{tag,{'PRIVATE',3}},{mode,implicit}]
ok
If the maximum depth has been reached, then it is impossible to read in the
resultant output. Also, the ,... form in a tuple denotes that there are more
elements in the tuple but these are below the print depth.
P:
Writes data in the same way as ~p, but takes an extra argument which is the
maximum depth to which terms are printed. Anything below this depth is replaced
with .... For example:
9> io:fwrite("~62P~n", [T,9]).
[{attributes,[[{id,age,1.5},{mode,explicit},{typename,...}],
[{id,cho},{mode,...},{...}]]},
{typename,'Person'},
{tag,{'PRIVATE',3}},
{mode,implicit}]
ok
B:
Writes an integer in base 2..36, the default base is 10. A leading dash is
printed for negative integers.
The precision field selects base. For example:
1> io:fwrite("~.16B~n", [31]).
1F
ok
2> io:fwrite("~.2B~n", [-19]).
-10011
ok
3> io:fwrite("~.36B~n", [5*36+35]).
5Z
ok
X:
Like B, but takes an extra argument that is a prefix to insert before the
number, but after the leading dash, if any.
The prefix can be a possibly deep list of characters or an atom.
1> io:fwrite("~X~n", [31,"10#"]).
10#31
ok
2> io:fwrite("~.16X~n", [-31,"0x"]).
-0x1F
ok
#:
Like B, but prints the number with an Erlang style #-separated base prefix.
1> io:fwrite("~.10#~n", [31]).
10#31
ok
2> io:fwrite("~.16#~n", [-31]).
-16#1F
ok
b:
Like B, but prints lowercase letters.
x:
Like X, but prints lowercase letters.
+:
Like #, but prints lowercase letters.
n:
Writes a new line.
i:
Ignores the next term.
Returns:
ok:
The formatting succeeded.
If an error occurs, there is no output. For example:
1> io:fwrite("~s ~w ~i ~w ~c ~n",['abc def', 'abc def', {foo, 1},{foo, 1}, 65]).
abc def 'abc def' {foo,1} A
ok
2> io:fwrite("~s", [65]).
** exception exit: {badarg,[{io,format,[<0.22.0>,"~s","A"]},
{erl_eval,do_apply,5},
{shell,exprs,6},
{shell,eval_exprs,6},
{shell,eval_loop,3}]}
in function io:o_request/2
In this example, an attempt was made to output the single character 65 with the aid
of the string formatting directive "~s".
fread(Prompt, Format) -> Result
fread(IoDevice, Prompt, Format) -> Result
Types:
IoDevice = device()
Prompt = prompt()
Format = format()
Result = {ok, Terms :: [term()]}
| {error, {fread, FreadError :: io_lib:fread_error()}}
| server_no_data()
server_no_data() = {error, ErrorDescription :: term()} | eof
Reads characters from the standard input (IoDevice), prompting it with Prompt.
Interprets the characters in accordance with Format. Format contains control
sequences which directs the interpretation of the input.
Format may contain:
* White space characters (SPACE, TAB and NEWLINE) which cause input to be read to
the next non-white space character.
* Ordinary characters which must match the next input character.
* Control sequences, which have the general format ~*FMC. The character * is an
optional return suppression character. It provides a method to specify a field
which is to be omitted. F is the field width of the input field, M is an
optional translation modifier (of which t is the only currently supported,
meaning Unicode translation) and C determines the type of control sequence.
Unless otherwise specified, leading white-space is ignored for all control
sequences. An input field cannot be more than one line wide. The following
control sequences are available:
~:
A single ~ is expected in the input.
d:
A decimal integer is expected.
u:
An unsigned integer in base 2..36 is expected. The field width parameter is
used to specify base. Leading white-space characters are not skipped.
-:
An optional sign character is expected. A sign character - gives the return
value -1. Sign character + or none gives 1. The field width parameter is
ignored. Leading white-space characters are not skipped.
#:
An integer in base 2..36 with Erlang-style base prefix (for example
"16#ffff") is expected.
f:
A floating point number is expected. It must follow the Erlang floating point
number syntax.
s:
A string of non-white-space characters is read. If a field width has been
specified, this number of characters are read and all trailing white-space
characters are stripped. An Erlang string (list of characters) is returned.
If Unicode translation is in effect (~ts), characters larger than 255 are
accepted, otherwise not. With the translation modifier, the list returned may
as a consequence also contain integers larger than 255:
1> io:fread("Prompt> ","~s").
Prompt> <Characters beyond latin1 range not printable in this medium>
{error,{fread,string}}
2> io:fread("Prompt> ","~ts").
Prompt> <Characters beyond latin1 range not printable in this medium>
{ok,[[1091,1085,1080,1094,1086,1076,1077]]}
a:
Similar to s, but the resulting string is converted into an atom.
The Unicode translation modifier is not allowed (atoms can not contain
characters beyond the latin1 range).
c:
The number of characters equal to the field width are read (default is 1) and
returned as an Erlang string. However, leading and trailing white-space
characters are not omitted as they are with s. All characters are returned.
The Unicode translation modifier works as with s:
1> io:fread("Prompt> ","~c").
Prompt> <Character beyond latin1 range not printable in this medium>
{error,{fread,string}}
2> io:fread("Prompt> ","~tc").
Prompt> <Character beyond latin1 range not printable in this medium>
{ok,[[1091]]}
l:
Returns the number of characters which have been scanned up to that point,
including white-space characters.
It returns:
{ok, Terms}:
The read was successful and Terms is the list of successfully matched and
read items.
eof:
End of file was encountered.
{error, FreadError}:
The reading failed and FreadError gives a hint about the error.
{error, ErrorDescription}:
The read operation failed and the parameter ErrorDescription gives a hint
about the error.
Examples:
20> io:fread('enter>', "~f~f~f").
enter>1.9 35.5e3 15.0
{ok,[1.9,3.55e4,15.0]}
21> io:fread('enter>', "~10f~d").
enter> 5.67899
{ok,[5.678,99]}
22> io:fread('enter>', ":~10s:~10c:").
enter>: alan : joe :
{ok, ["alan", " joe "]}
rows() -> {ok, integer() >= 1} | {error, enotsup}
rows(IoDevice) -> {ok, integer() >= 1} | {error, enotsup}
Types:
IoDevice = device()
Retrieves the number of rows of the IoDevice (i.e. the height of a terminal). The
function only succeeds for terminal devices, for all other IO devices the function
returns {error, enotsup}
scan_erl_exprs(Prompt) -> Result
scan_erl_exprs(Device, Prompt) -> Result
scan_erl_exprs(Device, Prompt, StartLocation) -> Result
scan_erl_exprs(Device, Prompt, StartLocation, Options) -> Result
Types:
Device = device()
Prompt = prompt()
StartLocation = location()
Options = erl_scan:options()
Result = erl_scan:tokens_result() | server_no_data()
server_no_data() = {error, ErrorDescription :: term()} | eof
Reads data from the standard input (IoDevice), prompting it with Prompt. Reading
starts at location StartLocation (1). The argument Options is passed on as the
Options argument of the erl_scan:tokens/4 function. The data is tokenized as if it
were a sequence of Erlang expressions until a final dot (.) is reached. This token
is also returned. It returns:
{ok, Tokens, EndLocation}:
The tokenization succeeded.
{eof, EndLocation}:
End of file was encountered by the tokenizer.
eof:
End of file was encountered by the I/O-server.
{error, ErrorInfo, ErrorLocation}:
An error occurred while tokenizing.
{error, ErrorDescription}:
Other (rare) error condition, for instance {error, estale} if reading from an
NFS file system.
Example:
23> io:scan_erl_exprs('enter>').
enter>abc(), "hey".
{ok,[{atom,1,abc},{'(',1},{')',1},{',',1},{string,1,"hey"},{dot,1}],2}
24> io:scan_erl_exprs('enter>').
enter>1.0er.
{error,{1,erl_scan,{illegal,float}},2}
scan_erl_form(Prompt) -> Result
scan_erl_form(IoDevice, Prompt) -> Result
scan_erl_form(IoDevice, Prompt, StartLocation) -> Result
scan_erl_form(IoDevice, Prompt, StartLocation, Options) -> Result
Types:
IoDevice = device()
Prompt = prompt()
StartLocation = location()
Options = erl_scan:options()
Result = erl_scan:tokens_result() | server_no_data()
server_no_data() = {error, ErrorDescription :: term()} | eof
Reads data from the standard input (IoDevice), prompting it with Prompt. Starts
reading at location StartLocation (1). The argument Options is passed on as the
Options argument of the erl_scan:tokens/4 function. The data is tokenized as if it
were an Erlang form - one of the valid Erlang expressions in an Erlang source file
- until a final dot (.) is reached. This last token is also returned. The return
values are the same as for scan_erl_exprs/1,2,3 above.
parse_erl_exprs(Prompt) -> Result
parse_erl_exprs(IoDevice, Prompt) -> Result
parse_erl_exprs(IoDevice, Prompt, StartLocation) -> Result
parse_erl_exprs(IoDevice, Prompt, StartLocation, Options) ->
Result
Types:
IoDevice = device()
Prompt = prompt()
StartLocation = location()
Options = erl_scan:options()
Result = parse_ret()
parse_ret() = {ok,
ExprList :: erl_parse:abstract_expr(),
EndLocation :: location()}
| {eof, EndLocation :: location()}
| {error,
ErrorInfo :: erl_scan:error_info()
| erl_parse:error_info(),
ErrorLocation :: location()}
| server_no_data()
server_no_data() = {error, ErrorDescription :: term()} | eof
Reads data from the standard input (IoDevice), prompting it with Prompt. Starts
reading at location StartLocation (1). The argument Options is passed on as the
Options argument of the erl_scan:tokens/4 function. The data is tokenized and
parsed as if it were a sequence of Erlang expressions until a final dot (.) is
reached. It returns:
{ok, ExprList, EndLocation}:
The parsing was successful.
{eof, EndLocation}:
End of file was encountered by the tokenizer.
eof:
End of file was encountered by the I/O-server.
{error, ErrorInfo, ErrorLocation}:
An error occurred while tokenizing or parsing.
{error, ErrorDescription}:
Other (rare) error condition, for instance {error, estale} if reading from an
NFS file system.
Example:
25> io:parse_erl_exprs('enter>').
enter>abc(), "hey".
{ok, [{call,1,{atom,1,abc},[]},{string,1,"hey"}],2}
26> io:parse_erl_exprs ('enter>').
enter>abc("hey".
{error,{1,erl_parse,["syntax error before: ",["'.'"]]},2}
parse_erl_form(Prompt) -> Result
parse_erl_form(IoDevice, Prompt) -> Result
parse_erl_form(IoDevice, Prompt, StartLocation) -> Result
parse_erl_form(IoDevice, Prompt, StartLocation, Options) -> Result
Types:
IoDevice = device()
Prompt = prompt()
StartLocation = location()
Options = erl_scan:options()
Result = parse_form_ret()
parse_form_ret() = {ok,
AbsForm :: erl_parse:abstract_form(),
EndLocation :: location()}
| {eof, EndLocation :: location()}
| {error,
ErrorInfo :: erl_scan:error_info()
| erl_parse:error_info(),
ErrorLocation :: location()}
| server_no_data()
server_no_data() = {error, ErrorDescription :: term()} | eof
Reads data from the standard input (IoDevice), prompting it with Prompt. Starts
reading at location StartLocation (1). The argument Options is passed on as the
Options argument of the erl_scan:tokens/4 function. The data is tokenized and
parsed as if it were an Erlang form - one of the valid Erlang expressions in an
Erlang source file - until a final dot (.) is reached. It returns:
{ok, AbsForm, EndLocation}:
The parsing was successful.
{eof, EndLocation}:
End of file was encountered by the tokenizer.
eof:
End of file was encountered by the I/O-server.
{error, ErrorInfo, ErrorLocation}:
An error occurred while tokenizing or parsing.
{error, ErrorDescription}:
Other (rare) error condition, for instance {error, estale} if reading from an
NFS file system.
STANDARD INPUT/OUTPUT
All Erlang processes have a default standard IO device. This device is used when no
IoDevice argument is specified in the above function calls. However, it is sometimes
desirable to use an explicit IoDevice argument which refers to the default IO device. This
is the case with functions that can access either a file or the default IO device. The
atom standard_io has this special meaning. The following example illustrates this:
27> io:read('enter>').
enter>foo.
{ok,foo}
28> io:read(standard_io, 'enter>').
enter>bar.
{ok,bar}
There is always a process registered under the name of user. This can be used for sending
output to the user.
STANDARD ERROR
In certain situations, especially when the standard output is redirected, access to an
I/O-server specific for error messages might be convenient. The IO device standard_error
can be used to direct output to whatever the current operating system considers a suitable
IO device for error output. Example on a Unix-like operating system:
$ erl -noshell -noinput -eval 'io:format(standard_error,"Error: ~s~n",["error 11"]),'\
'init:stop().' > /dev/null
Error: error 11
ERROR INFORMATION
The ErrorInfo mentioned above is the standard ErrorInfo structure which is returned from
all IO modules. It has the format:
{ErrorLocation, Module, ErrorDescriptor}
A string which describes the error is obtained with the following call:
Module:format_error(ErrorDescriptor)