bsd man page for expand

EXPAND(1)						      General Commands Manual							 EXPAND(1)

NAME
       expand, unexpand - expand tabs to spaces, and vice versa

SYNOPSIS
       expand [ -tabstop ] [ -tab1,tab2,...,tabn ] [ file ...  ]
       unexpand [ -a ] [ file ...  ]

DESCRIPTION
       Expand processes the named files or the standard input writing the standard output with tabs changed into blanks.  Backspace characters are
       preserved into the output and decrement the column count for tab calculations.  Expand is useful for pre-processing character files (before
       sorting, looking at specific columns, etc.) that contain tabs.

       If  a  single  tabstop  argument is given, then tabs are set tabstop spaces apart instead of the default 8.  If multiple tabstops are given
       then the tabs are set at those specific columns.

       Unexpand puts tabs back into the data from the standard input or the named files and writes the result on the standard output.  By default,
       only  leading  blanks and tabs are reconverted to maximal strings of tabs.  If the -a option is given, then tabs are inserted whenever they
       would compress the resultant file by replacing two or more characters.

4th Berkeley Distribution					    May 9, 1986 							 EXPAND(1)