Streams and Files

A stream is a special case of a file object that can only be accessed

sequentially. You have no real way to know, given an arbitrary file object,

whether or not you can read or write arbitrary parts of the file. It is best

always to assume that the file is a stream, and only to read sequentially

from it (or write sequentially to it). For example, the currentfile operator

will often return the file stream representing the serial port on the printer,

although it might represent a real disk file in an environment where there

is a file system available to the interpreter. As long as you use the

setfileposition operator with some care, the distinction between a stream

and a file probably won’t matter.

TIP

Some file operations will work on virtually any PostScript interpreter,

such as reading from the current file or writing to the standard output

stream. Other file operations, such as explicitly opening a file by name,

checking the status of a file, or using a very specific operator like set-

fileposition, depend heavily on the existence of a file system supported

by the interpreter. It is very important to make sure that the interpreter

supports these operations before attempting them, or you may get an er-

ror. You can use the known or where operators to check for the existence

of certain operators, or you can consult the manual for your interpreter to

find out how to test for the presence of a file system.

As a rule of thumb, any printer equipped with a hard disk or any worksta-

tion running a PostScript interpreter will have access to the full range of

disk operations described in this chapter.

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Chapter 14: USING FILES AND INPUT/OUTPUT TECHNIQUES

Arguments Operator

Action

string1 string2

file file_object

open file string1 with access string2

file_object

closefile

±

close file

string

deletefile†

remove file from device

string1 string2

renamefile†

±

change file name string1 to string2

pattern proc scratch filenameforall† ±

execute proc for files that match

pattern string (can use *)

file_object

read int true

read one character from file

false

file_object int

write

write one character to file

file_object string

readhexstring

read hexadecimal strings

substring

boolean

file_object string

writehexstring

write hexadecimal strings

file_object string

readstring

string

read string from file

file_object string

writestring

write string to file

file_object string

readline

string

read through newline

file_object

token token true

read PostScript token from file

false

file_object

bytesavailable† int

how many bytes left in file

flush

flush stdout file

file_object

flushfile

flush file_object

file_object

resetfile†

reset file pointer to beginning of file

file_object int

setfileposition†

set file position to int

file_object

fileposition† int

return current position in file

file_object

status†

boolean

is file_object still valid?

string

status†

pages

return information on disk file named

bytes

string and leave data on stack

referenced

created

or

true

false

diskstatus†

pages_used

total_pages

string

run

execute contents of file string

currentfile

file_object

returns currently active file object

Chapter 14: USING FILES AND INPUT/OUTPUT TECHNIQUES

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