Minimum working example:
x:=Indeterminate(Rationals,"x");
f:=Sum([1..1000],i->x^i);
PrintTo("~/temp.txt",f);
It prints to temp.txt
the following:
x^1000+x^999+x^998+x^997+x^996+x^995+x^994+x^993+x^992+x^991+x^990+x^989+x^988\
+x^987+x^986+x^985+x^984+x^983+x^982+x^981+x^980+x^979+x^978+x^977+x^976+x^975\
+x^974+x^973+x^972+x^971+x^970+x^969+x^968+x^967+x^966+x^965+x^964+x^963+x^962\
+x^961+x^960+x^959+x^958+x^957+x^956+x^955+x^954+x^953+x^952+x^951+x^950+x^949\
[snip]
How can I instead get it to print it on a single line in the text file?