9.1.3 Squeezing repeats and deleting

When given just the `--delete' (`-d') option, tr removes any input characters that are in set1.

When given just the `--squeeze-repeats' (`-s') option, tr replaces each input sequence of a repeated character that is in set1 with a single occurrence of that character.

When given both `--delete' and `--squeeze-repeats', tr first performs any deletions using set1, then squeezes repeats from any remaining characters using set2.

The `--squeeze-repeats' option may also be used when translating, in which case tr first performs translation, then squeezes repeats from any remaining characters using set2.

Here are some examples to illustrate various combinations of options:

• Remove all zero bytes:

  tr -d '\000'

• Put all words on lines by themselves. This converts all non-alphanumeric characters to newlines, then squeezes each string of repeated newlines into a single newline:

  tr -cs 'a-zA-Z0-9' '[\n*]'

• Convert each sequence of repeated newlines to a single newline:

  tr -s '\n'

• Find doubled occurrences of words in a document. For example, people often write "the the" with the duplicated words separated by a newline. The bourne shell script below works first by converting each sequence of punctuation and blank characters to a single newline. That puts each "word" on a line by itself. Next it maps all uppercase characters to lower case, and finally it runs uniq with the `-d' option to print out only the words that were adjacent duplicates.

  #!/bin/sh cat "$@" \ | tr -s '[:punct:][:blank:]' '\n' \ | tr '[:upper:]' '[:lower:]' \ | uniq -d