using Printf

# Reading files requires checking most calls for errors.
# This helper will streamline our error checks below.
function check(e)
    if e !== nothing
        error(e)
    end
end

# Perhaps the most basic file reading task is
# slurping a file's entire contents into memory.
dat = read("/tmp/dat", String)
print(dat)

# You'll often want more control over how and what
# parts of a file are read. For these tasks, start
# by opening a file to obtain an IOStream value.
f = open("/tmp/dat")

# Read some bytes from the beginning of the file.
# Allow up to 5 to be read but also note how many
# actually were read.
b1 = Vector{UInt8}(undef, 5)
n1 = readbytes!(f, b1)
@printf("%d bytes: %s\n", n1, String(b1[1:n1]))

# You can also seek to a known location in the file
# and read from there.
seek(f, 6)
b2 = Vector{UInt8}(undef, 2)
n2 = readbytes!(f, b2)
@printf("%d bytes @ %d: ", n2, position(f) - n2)
@printf("%s\n", String(b2[1:n2]))

# Other methods of seeking are relative to the
# current cursor position,
skip(f, 4)

# and relative to the end of the file.
seekend(f)
skip(f, -10)

# The Base package provides some functions that may
# be helpful for file reading. For example, reads
# like the ones above can be more robustly
# implemented with read!.
seek(f, 6)
b3 = Vector{UInt8}(undef, 2)
n3 = read!(f, b3)
@printf("%d bytes @ %d: %s\n", n3, position(f) - n3, String(b3))

# There is no built-in rewind, but
# seek(f, 0) accomplishes this.
seek(f, 0)

# The Base package implements a buffered
# reader that may be useful both for its efficiency
# with many small reads and because of the additional
# reading methods it provides.
r4 = IOBuffer(read(f))
b4 = Base.peek(r4, UInt8, 5)
@printf("5 bytes: %s\n", String(b4))

# Close the file when you're done (usually this would
# be scheduled immediately after opening with
# try/finally or do block).
close(f)