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3.17 Primitive Character Input and Output

nl
Write a newline character to the current output stream. On Unix systems nl/0 is equivalent to put(10).

nl(+Stream)
Write a newline to Stream.

put(+Char)
Write Char to the current output stream, Char is either an integer-expression evaluating to an ASCII value (0 =<Char =< 255) or an atom of one character.

put(+Stream, +Char)
Write Char to Stream.

tab(+Amount)
Writes Amount spaces on the current output stream. Amount should be an expression that evaluates to a positive integer (see section 3.23).

tab(+Stream, +Amount)
Writes Amount spaces to Stream.

flush
Flush pending output on current output stream. flush/0 is automatically generated by read/1 and derivatives if the current input stream is user and the cursor is not at the left margin.

flush_output(+Stream)
Flush output on the specified stream. The stream must be open for writing.

ttyflush
Flush pending output on stream user. See also flush/0.

get0(-Char)
Read the current input stream and unify the next character with Char. Char is unified with -1 on end of file.

get0(+Stream, -Char)
Read the next character from Stream.

get(-Char)
Read the current input stream and unify the next non-blank character with Char. Char is unified with -1 on end of file.

get(+Stream, -Char)
Read the next non-blank character from Stream.

peek_byte(-Char)
Reads the next input character like get0/1, but does not remove it from the input stream. This predicate is ISO compliant.

peek_byte(+Stream, -Char)
Reads the next input character like get0/2, but does not remove it from the stream. This predicate is ISO compliant.

skip(+Char)
Read the input until Char or the end of the file is encountered. A subsequent call to get0/1 will read the first character after Char.

skip(+Stream, +Char)
Skip input (as skip/1) on Stream.

get_single_char(-Char)
Get a single character from input stream `user' (regardless of the current input stream). Unlike get0/1 this predicate does not wait for a return. The character is not echoed to the user's terminal. This predicate is meant for keyboard menu selection etc.. If SWI-Prolog was started with the -tty option this predicate reads an entire line of input and returns the first non-blank character on this line, or the ASCII code of the newline (10) if the entire line consisted of blank characters.

at_end_of_stream
Succeeds after the last character of the current input stream has been read. Also succeeds if there is no valid current input stream.

at_end_of_stream(+Stream)
Succeeds after the last character of the named stream is read, or Stream is not a valid input stream.