first and last lines of a file

Define it as an alias: Make it available as a more general function: column -t is usefull when you work frequently with table-like text files.

tree as an alternative to ls

ls -lha
total 1,2G
drwxrwxr-x 3 alex alex 4,0K Nov 15 09:48 .
drwxr-xr-x 4 alex alex 4,0K Nov 14 15:46 ..
drwxrwxr-x 4 alex alex 4,0K Nov 15 09:41 Homo_sapiens
-rw-rw-r-- 1 alex alex 1,2G Nov 15 10:17 Homo_sapiens_Ensembl_GRCh37.tar.gz
tree -pfuih --du
.
[drwxrwxr-x alex     215G]  ./Homo_sapiens
[drwxrwxr-x alex      52G]  ./Homo_sapiens/Ensembl
[drwxrwxr-x alex      52G]  ./Homo_sapiens/Ensembl/GRCh37
[drwxrwxr-x alex      30G]  ./Homo_sapiens/Ensembl/GRCh37/Annotation
[drwxrwxr-x alex      30G]  ./Homo_sapiens/Ensembl/GRCh37/Annotation/Archives
[drwxrwxr-x alex     525M]  ./Homo_sapiens/Ensembl/GRCh37/Annotation/Archives/archive-2010-09-28-01-21-46
[-rwxrwxr-x alex      302]  ./Homo_sapiens/Ensembl/GRCh37/Annotation/Archives/archive-2010-09-28-01-21-46/ChromInfo.txt
[..]

unix mv command without overriding existing files

Per default, mv will override existing files with the same name. To rename existing files with the same name instead, use the backup parameter.
mv --backup=numbered
The resulting file name pattern is [filename].[extension].~[number]~, e.g. image.jpg.~1~. Note that these files can be recognized as recycle or backup files by mistake. In this case they might be hidden by your file manager.