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coreutils: unexpand invocation

 
 9.3 ‘unexpand’: Convert spaces to tabs
 ======================================
 
 ‘unexpand’ writes the contents of each given FILE, or standard input if
 none are given or for a FILE of ‘-’, to standard output, converting
 blanks at the beginning of each line into as many tab characters as
 needed.  In the default POSIX locale, a “blank” is a space or a tab;
 other locales may specify additional blank characters.  Synopsis:
 
      unexpand [OPTION]... [FILE]...
 
    By default, ‘unexpand’ converts only initial blanks (those that
 precede all non-blank characters) on each line.  It preserves backspace
 characters in the output; they decrement the column count for tab
 calculations.  By default, tabs are set at every 8th column.
 
    The program accepts the following options.  Also see ⇒Common
 options.
 
 ‘-t TAB1[,TAB2]...’
 ‘--tabs=TAB1[,TAB2]...’
      If only one tab stop is given, set the tabs TAB1 columns apart
      instead of the default 8.  Otherwise, set the tabs at columns TAB1,
      TAB2, ... (numbered from 0), and leave blanks beyond the tab stops
      given unchanged.  Tab stops can be separated by blanks as well as
      by commas.
 
      As a GNU extension the last TAB specified can be prefixed with a
      ‘/’ to indicate a tab size to use for remaining positions.  For
      example, ‘--tabs=2,4,/8’ will set tab stops at position 2 and 4,
      and every multiple of 8 after that.
 
      Also the last TAB specified can be prefixed with a ‘+’ to indicate
      a tab size to use for remaining positions, offset from the final
      explicitly specified tab stop.  For example, to ignore the 1
      character gutter present in diff output, one can specify a 1
      character offset using ‘--tabs=1,+8’, which will set tab stops at
      positions 1,9,17,...
 
      This option implies the ‘-a’ option.
 
      For compatibility, GNU ‘unexpand’ supports the obsolete option
      syntax, ‘-TAB1[,TAB2]...’, where tab stops must be separated by
      commas.  (Unlike ‘-t’, this obsolete option does not imply ‘-a’.)
      New scripts should use ‘--first-only -t TAB1[,TAB2]...’ instead.
 
 ‘-a’
 ‘--all’
      Also convert all sequences of two or more blanks just before a tab
      stop, even if they occur after non-blank characters in a line.
 
    An exit status of zero indicates success, and a nonzero value
 indicates failure.
 

Info Catalog coreutils: expand invocation coreutils: Operating on characters