Read numerical data from text files

The sample data files are
v.dat 25 numbers, in Fortran/C "E" notation
xy.dat 30 lines, each with an x and a y value
m.dat 45 numbers, several per line


1. Read in & define array v with all (25) values from the file v.dat
2. Read in & define arrays x and y with the 1st and 2nd columns (respectively) of file xy.dat
3. Read in & define 3×5 matrix M with the first 15 numbers in file m.dat


v = ReadList[ "v.dat", Number ]

xy = ReadList["xy.dat",{Number,Number}];
x = xy[[All,1]]
y = xy[[All,2]]

m = ReadList[ "m.dat", Table[Number,{5}], 3]


Write data to a file

For this example, A is a 10×3 array of values, where the first column are
the x values 1 through 10, the second column are the y values where
y=sqrt(x), and the third column are the z values where z=x2.
 1    1.        1
 2    1.41421   4
 3    1.73205   9
 4    2.        16
 5    2.23607   25
 6    2.44949   36
 7    2.64575   49
 8    2.82843   64
 9    3.        81
10    3.16228   100
1. create 10×3 array A
A = Table[{n,N[Sqrt[n]],n^2},{n,10}]

2. write the values of A to a text file A.dat, one row per line
Export["A.dat", A, "Table"]


3. generate a 7×11 matrix R of random values (uniform on [0,1]),
    and write them to file ranm.dat, four elements per line
R = Table[Random[], {7},{11}];

R4 = Partition[Flatten[{R,"","",""}],4]
OutputForm[TableForm[R4,TableSpacing->{0}]]>>ranm.dat