Question: The one-liner should:

* solve a real-world problem
* not be extensively cryptic (should be easy to understand and reproduce)
* be worth the time it takes to write it (should not be too clever)

I'm looking for practical tips and tricks (complementary examples for `perldoc perlrun`).

Answer: 
The Perl one-liner I use the most is the Perl calculator

```
perl -ple '$_=eval'

```
I often need to see a readable version of the PATH while shell scripting. The following one-liners print every path entry on its own line.

Over time this one-liner has evolved through several phases:

Unix (version 1):

```
perl -e 'print join("\n",split(":",$ENV{"PATH"}))."\n"'

```

Windows (version 2):

```
perl -e "print join(qq(\n),split(';',$ENV{'PATH'})).qq(\n)"

```

Both Unix/Windows (using q/qq tip from @j-f-sebastian) (version 3):

```
perl -MFile::Spec -e 'print join(qq(\n), File::Spec->path).qq(\n)' # Unix
perl -MFile::Spec -e "print join(qq(\n), File::Spec->path).qq(\n)" # Windows

```