Question

What is the difference between these two code snippets?

1. open (MYFILE, '>>data.txt');

2. open (MYFILE, '>data.txt');

Answer 1

1. open (MYFILE, '>>data.txt') — Open data.txt, keep the original data, append data from the end.
2. open (MYFILE, '>data.txt') — Open data.txt, delete everything inside, and write data from the start.

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From perldoc -f open:

If MODE is '<' or nothing, the file is opened for input. If MODE is '>', the file is truncated and opened for output, being created if necessary. If MODE is '>>', the file is opened for appending, again being created if necessary.

It stems from the shell usage that,

• cmd < file.txt to copy file into stdin,
• cmd > file.txt to write stdout into a file, and
• cmd >> file.txt to append stdout to the end of the file.