To write lines of text to a file, use the LINEOUT method. By default, LINEOUT appends to an existing file. The following example adds an item to a to-do list that is maintained as a simple text file:
/* TODO.CMD -- add to a todo list */
parse arg text
file=.stream~new('todo.dat') /* Create a stream object */
file~lineout(date() time() text) /* Append a line to the file */
exit
In TODO.CMD, a text string is provided as the only argument on LINEOUT. REXX writes the line of text to the file and then writes a new-line character. You do not have to provide a new-line character in the string being written.
If you want to overwrite a file, specify a line number as a second argument. When a line number is specified, REXX uses it to position the write pointer before writing:
file~lineout('13760-0006',35) /* Replace line 35 */
For text files, write positioning has a somewhat specialized use. REXX does not prevent you from overwriting existing new-line characters in the file. REXX writes whatever line you give it at whatever write position you tell it to use. Consequently, if you want to replace a line of the file without overlaying following lines, the line you write must be exactly the same length as the line you are replacing. Writing a line that's shorter than an existing line will leave part of the old line in the file.
Also, don't assume that positioning the write pointer to line 1 will cause the file to be replaced. Yes, REXX will start writing over the existing data starting at line 1, but if you happen to write fewer bytes than previously existed in the file, your data will be followed by the remainder of the old file.
To replace a file, use the OPEN method with WRITE REPLACE or BOTH REPLACE as an argument. In the following example, a file named TEMP.DAT is replaced with a random number of lines. TEMP.DAT is then read and displayed. You can run the example repeatedly to verify that TEMP.DAT is replaced on each run.
/* REPFILE.CMD -- demonstrates file replacement */
testfile=.stream~new('temp.dat') /* Create a new stream object */
testfile~open('both replace') /* Open for read, write, and replace */
numlines=random(1,100) /* Pick a number from 1 to 100 */
runid=random(1,9999) /* Pick a run identifier */
do i=1 to numlines /* Write the lines */
testfile~lineout('Run ID:'||runid 'Line number' i)
end
/* Now read and display the file. The read pointer is already at the */
/* beginning of the file. MAKEARRAY reads from the read position to */
/* the end of the file and returns an array object containing the */
/* lines. */
filedata=testfile~makearray('line')
do i over filedata
say i
end
testfile~close
The REPFILE example also demonstrates that REXX maintains separate read and write pointers to a stream. Notice that we started reading without repositioning the read pointer. Since we hadn't yet read anything, the read pointer was still at the beginning of the file. The write pointer, however, is at the end of the file.