Chapter 6: Perl One-Liners：Text Conversion and Substitution

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

change, convert, and substitute text,
including base64 encoding and decoding,
URL escaping andunescaping,
HTML escaping and unescaping,
converting text case,
reversing lines.

You’ll also get to know the y, tr, uc, lc, and reverse operators and string-escape sequences.

6.1 ROT13 a string

      perl -le '$string = "bananas"; $string =~ y/A-Za-z/N-ZA-Mn-za-m/; print $string'

To ROT13 the whole file bananas.txt and print it to the screen, just do this:

  perl -lpe 'y/A-Za-z/N-ZA-Mn-za-m/' bananas.txt

You can also use Perl’s -i argument to do in-place replacement of the file. For example, to ROT13 oranges.txt in-place, write this:

    perl -pi.bak -e 'y/A-Za-z/N-ZA-Mn-za-m/' oranges.txt

6.2 Base64-encode a string

    perl -MMIME::Base64 -e 'print encode_base64("string")'

To base64-encode the whole file, use this:

  perl -MMIME::Base64 -0777 -ne 'print encode_base64($_)' file

6.3 Base64-decode a string

    perl -MMIME::Base64 -le 'print decode_base64("base64string")'

6.4 URL -escape a string

    perl -MURI::Escape -le 'print uri_escape("http://example.com")'

6.5 URL -unescape a string

        perl -MURI::Escape -le 'print uri_unescape("http%3A%2F%2Fexample.com")'

6.6 HTML -encode a string

    perl -MHTML::Entities -le 'print encode_entities("<html>")'

6.7 HTML -decode a string

      perl -MHTML::Entities -le 'print decode_entities("&lt;html&gt;")'

6.8 Convert all text to uppercase

  perl -nle 'print uc'

Or you can apply the \U escape sequence to string interpolation:

  perl -nle 'print "\U$_"'

6.9 Convert all text to lowercase

    perl -nle 'print lc'

6.10 Uppercase only the first letter of each line

    perl -nle 'print ucfirst lc'

You can do the same thing using escape codes and string interpolation:

    perl -nle 'print "\u\L$_"'

6.11 Invert the letter case

      perl -ple 'y/A-Za-z/a-zA-Z/'

6.12 Title-case each line

    perl -ple 's/(\w+)/\u$1/g'

6.13 Strip leading whitespace (spaces, tabs) from the beginning of each line

    perl -ple 's/^[ \t]+//'

6.14 Strip trailing whitespace (spaces, tabs) from the end of each line

      perl -ple 's/[ \t]+$//'

6.15 Strip whitespace (spaces, tabs) from the beginning and end of each line

        perl -ple 's/^[ \t]+|[ \t]+$//g'

6.16 Convert UNIX newlines to DOS/Windows newlines

      perl -pe 's|\012|\015\012|'

6.17 Convert DOS/Windows newlines to UNIX newlines

    perl -pe 's|\015\012|\012|'

6.18 Convert UNIX newlines to Mac newlines

        perl -pe 's|\012|\015|'

6.19 Substitute (find and replace) “foo” with “bar” on each line

    perl -pe 's/foo/bar/'

6.20 Substitute (find and replace) “foo” with “bar” on lines that match “baz”

      perl -pe '/baz/ && s/foo/bar/'

6.21 Print paragraphs in reverse order

        perl -00 -e 'print reverse <>' file

6.22 Print all lines in reverse order

    perl -lne 'print scalar reverse $_'

6.23 Print columns in reverse order

    perl -alne 'print "@{[reverse @F]}"'

Notice, however, that the : characters are missing in this output. To get them back, you need to modify the one-liner a bit and set the $" variable to ":", as shown here:

      perl -F: -alne '$" = ":"; print "@{[reverse @F]}"'