Squeeze Repeats

One option that I have seldom used in tr command is -s or --squeeze-repeats:

replace each sequence of a repeated character that is listed in the last specified SET, with a single occurrence of that character - TR(1)

The best way to explain it is to demonstrate by example:

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$ echo hello hello | tr l 1
he11o he11o

Apply the -s option:

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$ echo hello hello | tr -s l 1
he1o he1o

The number of repeated character 1 has been squeezed into a single occurrence.

Therefore, the tr command has the following three operations:

  • Translate (default, no options)
  • Delete (-d)
  • Squeeze (-s)

To drop repeated characters, the second set is not necessary. This is very useful to remove extra spaces:

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$ echo 'hello,     world!' | tr -s '[:blank]'
hello, world!

In Vim, to squeeze the extra blank in a line:

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:.! tr -s [:blank:]

Additional examples from GNU Coreutils Manual.

Delete blank lines:

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$ tr -s '\n'

Put all words on lines by themselves:

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$ tr -cs '[:alnum:]' '\n'

Quick summary for above mentioned use cases:

  • Remove extra spaces
  • Delete blank lines
  • Put all words on lines by themselves

Notes:

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tr (GNU coreutils) 8.29