In the Unix design, one tries to avoid creating a Swiss Army knife; instead, one creates a tool for a very specific, designated purpose and for that one purpose only. No ifs, no buts; no cruft, no clutter. This is design simplicity at its best.

Take a common example: when working on the Linux CLI (command-line interface), you would like to figure out which of your locally mounted filesystems has the most available (disk) space.

We can get the list of locally mounted filesystems by an appropriate switch (just df would do as well):

$ df --local
Filesystem                1K-blocks    Used Available Use% Mounted on
rootfs                     20640636 1155492  18436728   6% /
udev                          10240       0     10240   0% /dev
tmpfs                         51444     160     51284   1% /run
tmpfs                          5120       0      5120   0% /run/lock
tmpfs                        102880       0    102880   0% /run/shm
$ 

To sort the output, one would need to first save it to a file; one could use a temporary file for this purpose, tmp, and then sort it, using the sort utility, of course. Finally, we delete the offending temporary file. (Yes, there's a better way, piping; refer to the, Combine tools seamlessly section)

Note that the available space is the fourth column, so we sort accordingly:

$ df --local > tmp
$ sort -k4nr tmp
rootfs                     20640636 1155484  18436736   6% /
tmpfs                        102880       0    102880   0% /run/shm
tmpfs                         51444     160     51284   1% /run
udev                          10240       0     10240   0% /dev
tmpfs                          5120       0      5120   0% /run/lock
Filesystem                1K-blocks    Used Available Use% Mounted on
$ 

Whoops! The output includes the heading line. Let's first use the versatile sed utility – a powerful non-interactive editor tool – to eliminate the first line, the header, from the output of df:

$ df --local > tmp
$ sed --in-place '1d' tmp
$ sort -k4nr tmp
rootfs                     20640636 1155484  18436736   6% /
tmpfs                        102880       0    102880   0% /run/shm
tmpfs                         51444     160     51284   1% /run
udev                          10240       0     10240   0% /dev
tmpfs                          5120       0      5120   0% /run/lock
$ rm -f tmp

So what? The point is, on Unix, there is no one utility to list mounted filesystems and sort them by available space simultaneously. 

Instead, there is a utility to list mounted filesystems: df. It does a great job of it, with option switches to choose from. (How does one know which options? Learn to use the man pages, they're extremely useful.)

There is a utility to sort text: sort. Again, it's the last word in sorting text, with plenty of option switches to choose from for pretty much every conceivable sort one might require.

As expected, we obtain the results. So what exactly is the point? It's this: we used three utilities, not one. df , to list the mounted filesystems (and their related metadata), sed, to eliminate the header line, and sort, to sort whatever input its given (in any conceivable manner).

df can query and list mounted filesystems, but it cannot sort them. sort can sort text; it cannot list mounted filesystems.

Think about that for a moment.

Combine them all, and you get more than the sum of its parts! Unix tools typically do one task and they do it to its logical conclusion; no one does it better!