The Open Group Base Specifications Issue 7
IEEE Std 1003.1, 2013 Edition
Copyright © 2001-2013 The IEEE and The Open Group

#### NAME

> expand - convert tabs to spaces

#### SYNOPSIS

> ``expand` [`-t` tablist] [file`...`]`

#### DESCRIPTION

> The expand utility shall write files or the standard input to the standard output with <tab> characters replaced with one or more <space> characters needed to pad to the next tab stop. Any <backspace> characters shall be copied to the output and cause the column position count for tab stop calculations to be decremented; the column position count shall not be decremented below zero.

#### OPTIONS

> The expand utility shall conform to XBD Utility Syntax Guidelines.

> The following option shall be supported:

> -t tablist
>   Specify the tab stops. The application shall ensure that the argument tablist consists of either a single positive decimal integer or a list of tabstops. If a single number is given, tabs shall be set that number of column positions apart instead of the default 8.

>   If a list of tabstops is given, the application shall ensure that it consists of a list of two or more positive decimal integers, separated by <blank> or <comma> characters, in ascending order. The <tab> characters shall be set at those specific column positions. Each tab stop N shall be an integer value greater than zero, and the list is in strictly ascending order. This is taken to mean that, from the start of a line of output, tabbing to position N shall cause the next character output to be in the (N+1)th column position on that line.

>   In the event of expand having to process a <tab> at a position beyond the last of those specified in a multiple tab-stop list, the <tab> shall be replaced by a single <space> in the output.

#### OPERANDS

> The following operand shall be supported:

> file
>   The pathname of a text file to be used as input.

#### STDIN

> See the INPUT FILES section.

#### INPUT FILES

> Input files shall be text files.

#### ENVIRONMENT VARIABLES

> The following environment variables shall affect the execution of expand:

> LANG
>   Provide a default value for the internationalization variables that are unset or null. (See XBD Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.)
> LC_ALL
>   If set to a non-empty string value, override the values of all the other internationalization variables.
> LC_CTYPE
>   Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multi-byte characters in arguments and input files), the processing of <tab> and <space> characters, and for the determination of the width in column positions each character would occupy on an output device.
> LC_MESSAGES
>   Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.
> NLSPATH
>   [XSI] Determine the location of message catalogs for the processing of LC_MESSAGES.

#### ASYNCHRONOUS EVENTS

> Default.

#### STDOUT

> The standard output shall be equivalent to the input files with <tab> characters converted into the appropriate number of <space> characters.

#### STDERR

> The standard error shall be used only for diagnostic messages.

#### OUTPUT FILES

> None.

#### EXTENDED DESCRIPTION

> None.

#### EXIT STATUS

> The following exit values shall be returned:

> 0
>   Successful completion
> >0
>   An error occurred.

#### CONSEQUENCES OF ERRORS

> The expand utility shall terminate with an error message and non-zero exit status upon encountering difficulties accessing one of the file operands.

The following sections are informative.

#### APPLICATION USAGE

> None.

#### EXAMPLES

> None.

#### RATIONALE

> The expand utility is useful for preprocessing text files (before sorting, looking at specific columns, and so on) that contain <tab> characters.

> See XBD Column Position.

> The tablist option-argument consists of integers in ascending order. Utility Syntax Guideline 8 mandates that expand shall accept the integers (within the single argument) separated using either <comma> or <blank> characters.

> Earlier versions of this standard allowed the following form in the SYNOPSIS:

>     expand [-tabstop][-tab1,tab2,...,tabn][file ...]

> This form is no longer specified by POSIX.1-2008 but may be present in some implementations.

#### FUTURE DIRECTIONS

> None.

#### SEE ALSO

> tabs, unexpand

> XBD Column Position, Environment Variables, Utility Syntax Guidelines

#### CHANGE HISTORY

> First released in Issue 4.

#### Issue 6

> This utility is marked as part of the User Portability Utilities option.

> The APPLICATION USAGE section is added.

> The obsolescent SYNOPSIS is removed.

> The LC_CTYPE environment variable description is updated to align with the IEEE P1003.2b draft standard.

> The normative text is reworded to avoid use of the term "must" for application requirements.

#### Issue 7

> Austin Group Interpretation 1003.1-2001 #027 is applied.

> SD5-XCU-ERN-97 is applied, updating the SYNOPSIS.

> The expand utility is moved from the User Portability Utilities option to the Base. User Portability Utilities is now an option for interactive utilities.

End of informative text.

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