.\"	$OpenBSD: expand.1,v 1.16 2010/09/03 11:09:28 jmc Exp $
.\"	$NetBSD: expand.1,v 1.3 1995/09/02 06:19:45 jtc Exp $
.\"
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.\" are met:
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.\"	@(#)expand.1	8.1 (Berkeley) 6/9/93
.\"
.Dd $Mdocdate: September 3 2010 $
.Dt EXPAND 1
.Os
.Sh NAME
.Nm expand ,
.Nm unexpand
.Nd expand tabs to spaces, and vice versa
.Sh SYNOPSIS
.Nm expand
.Op Fl t Ar tablist
.Op Ar
.Nm unexpand
.Op Fl a
.Op Ar
.Sh DESCRIPTION
.Nm 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.
.Nm expand
is useful for pre-processing character files
(before sorting, looking at specific columns, etc.) that
contain tabs.
.Pp
.Nm unexpand
puts tabs back into the data from the standard input or the named
files and writes the result on the standard output.
.Pp
The options are as follows:
.Bl -tag -width flag
.It Fl a
.Pq Nm unexpand No only
By default, only leading blanks and tabs
are reconverted to maximal strings of tabs.
If the
.Fl a
option is given, tabs are inserted whenever they would compress the
resultant file by replacing two or more characters.
.It Fl t Ar tablist
.Pq Nm expand No only
If the argument to
.Fl t ,
.Ar tablist ,
consists of a single numerical argument, tabs are set
.Ar tablist
spaces apart instead of the default 8.
If multiple
.Fl t
options are given, then the tabs are set at those
specific columns.
.Pp
Otherwise the argument to
.Fl t
may consist of a list
of two or more positive decimal integers,
comma separated,
in ascending order:
in the event of having to process a
.Aq tab
at a position beyond the last of those specified in a multiple
.Fl t
list,
the
.Aq tab
is replaced by a single
.Aq space
character.
.Pp
This implementation of
.Nm
additionally allows
.Ar tablist
to be specified without using the
.Fl t
flag, by prefixing
.Ar tablist
with a dash
.Pq - .
.El
.Sh EXIT STATUS
.Ex -std expand
.Sh SEE ALSO
.Xr fold 1
.Sh STANDARDS
The
.Nm
and
.Nm unexpand
utilities are compliant with the
.St -p1003.1-2008
specification,
with the following exceptions:
.Bl -bullet -offset indent
.It
.Tn POSIX
does not support specifying tabstops without use of the
.Fl t
flag.
.It
.Tn POSIX
specifies that multiple tabstops may be given separated by
commas or blanks.
This implementation supports only comma-separated tabstops.
.It
.Nm unexpand
does not recognise the
.Fl t
flag.
.El
.Sh HISTORY
The
.Nm expand
command appeared in
.Bx 3.0 .