Chapter 5:Perl One-Liners：Workin

In this chapter, we’ll look at various one-liners for

• creating strings and arrays,
• for doing things like generating passwords,
• creating strings of certain length,
• finding the numeric values of characters,
• creating arrays of numbers.

You’ll also learn about the range operator .., the x operator, the $, special variable, and the @ARGV array.

5.1 Generate and print the alphabet

    perl -le 'print a..z'

The $, is the field separator. It’s output by print between each field. Semantically, though, using join to separate the list of letters with a comma is more appealing because it works even when not using print directly:

    perl -le '$alphabet = join ",", ("a".."z"); print $alphabet'

5.2 Generate and print all the strings from “a” to “zz”

5.3 Create a hex lookup table

perl -le '
$num = 255;
@hex = (0..9, "a".."f");
while ($num) {
$s = $hex[($num % 16)].$s;
$num = int $num/16;
}
print $s
'

But surely, converting a number to hex is much easier if I use printf(or sprintf) with the %x format specifier.

    perl -le 'printf("%x", 255)'

To convert the number back from hex to dec, use the hex operator:

    perl -le '$num = "ff"; print hex $num'

5.4 Generate a random eight-character password

        perl -le 'print map { ("a".."z")[rand 26] } 1..8'

5.5 Create a string of specific length

    perl -le 'print "a"x50'

For example, if you need 1KB of data, just
do this:

    perl -e 'print "a"x1024'

When you use the repetition operator in the list context, with a list as its first operand, you create a list with the given elements repeated, like this:

    perl -le '@list = (1,2)x20; print "@list"'

5.6 Create an array from a string

    @months = split ' ', "Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec"

5.7 Create a string from the command-line arguments

    perl -le 'print "(", (join ",", @ARGV), ")"' val1 val2 val3

5.8 Find the numeric values for characters in a string

    perl -le 'print join ", ", map { ord } split //, "hello world"'

You could also do this with the unpack operator by specifying C* as the unpacking template:

    perl -le 'print join ", ", unpack("C*", "hello world")'

5.9 Convert a list of numeric ASCII values into a string

perl -le '
@ascii = (99, 111, 100, 105, 110, 103);
print pack("C*", @ascii)
'

You can also use the @ARGV array and pass the ASCII values as arguments to the one-liner:

    perl -le 'print map chr, @ARGV' 99 111 100 105 110 103

5.10 Generate an array with odd numbers from 1 to 100

  perl -le '@odd = grep {$_ % 2 == 1} 1..100; print "@odd"'

5.11 Generate an array with even numbers from 1 to 100

      perl -le '@even = grep {$_ % 2 == 0} 1..100; print "@even"'

5.12 Find the length of a string

    perl -le 'print length "one-liners are great"'

5.13 Find the number of elements in an array

    perl -le '@array = ("a".."z"); print scalar @array'