Format output to a specific line length

Use fold as follows:

fold -s -w80 file

This will only split at whitespace (-s), using a line width of 80 characters (-w80). So it does exactly the same as the fmt solutions, but it also allows to break at any character when omitting the -s option.

Use fmt instead:

fmt --width=80 file

From man fmt:

-w, --width=WIDTH
              maximum line width (default of 75 columns)

Below mentioned solution might help:

cat file_name.txt | fmt -w 80 > reduced_file_name.txt

fmt - simple optimal text formatter.