# IO commands

To read or write on a file in Fortran one must first *open* it. To open a file name mytextfile.txt one can write

`open(unit=10, file="mytextfile.txt", status = new/old, action = read/write)`

Only the first two argument (unit and file) are mandatory. You can choose any integer for unit (it can also be a variable integer), as long as it is not used by another file (for example mytextfile\_2.txt).

After working on the file, you need to close it with the command

`close(10)`

## Reading

Fortran will read line by line, so if your file is a data file with one observation per line and 5 variables, say, you can get this data into a matrix in the following way

```
do j=1,15  
   read(10,*) var1(j) var2(j) var3(j) var4(j) var5(j)  
end do
```

## Writing

To write in a file, if you have a matrix with N lines with an identifier and a result (scalar) you can write

```
do j=1,N
  write(10,*) (matresult(j,i),i=1,2)
end do
```


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