echo

The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.

#### NAME

> echo - write arguments to standard output

#### SYNOPSIS

> ``echo` [string `...`]`

#### DESCRIPTION

> The echo utility writes its arguments to standard output, followed by a <newline>. If there are no arguments, only the <newline> is written.

#### OPTIONS

> The echo utility shall not recognize the `"--"` argument in the manner specified by Guideline 10 of the Base Definitions volume of IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines; `"--"` shall be recognized as a string operand.

> Implementations shall not support any options.

#### OPERANDS

> The following operands shall be supported:

> string
>   A string to be written to standard output. If the first operand is -n, or if any of the operands contain a backslash ( `'\'` ) character, the results are implementation-defined.

>   [XSI] On XSI-conformant systems, if the first operand is -n, it shall be treated as a string, not an option. The following character sequences shall be recognized on XSI-conformant systems within any of the arguments:

>   `\a`
>     Write an <alert>.
>   `\b`
>     Write a <backspace>.
>   `\c`
>     Suppress the <newline> that otherwise follows the final argument in the output. All characters following the `'\c'` in the arguments shall be ignored.
>   `\f`
>     Write a <form-feed>.
>   `\n`
>     Write a <newline>.
>   `\r`
>     Write a <carriage-return>.
>   `\t`
>     Write a <tab>.
>   `\v`
>     Write a <vertical-tab>.
>   `\\`
>     Write a backslash character.
>   `\0`num
>     Write an 8-bit value that is the zero, one, two, or three-digit octal number num.

#### STDIN

> Not used.

#### INPUT FILES

> None.

#### ENVIRONMENT VARIABLES

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

> LANG
>   Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume of IEEE Std 1003.1-2001, Section 8.2, 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
>   [XSI] 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).
> 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 echo utility arguments shall be separated by single <space>s and a <newline> shall follow the last argument. [XSI] Output transformations shall occur based on the escape sequences in the input. See the OPERANDS section.

#### 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

> Default.

The following sections are informative.

#### APPLICATION USAGE

> It is not possible to use echo portably across all POSIX systems unless both -n (as the first argument) and escape sequences are omitted.

> The printf utility can be used portably to emulate any of the traditional behaviors of the echo utility as follows (assuming that IFS has its standard value or is unset):

> - The historic System V echo and the requirements on XSI implementations in this volume of IEEE Std 1003.1-2001 are equivalent to:

>       printf "%b\n" "$*"

> - The BSD echo is equivalent to:

>       if [ "X$1" = "X-n" ]
>       then
>           shift
>           printf "%s" "$*"
>       else
>           printf "%s\n" "$*"
>       fi

> New applications are encouraged to use printf instead of echo.

#### EXAMPLES

> None.

#### RATIONALE

> The echo utility has not been made obsolescent because of its extremely widespread use in historical applications. Conforming applications that wish to do prompting without <newline>s or that could possibly be expecting to echo a -n, should use the printf utility derived from the Ninth Edition system.

> As specified, echo writes its arguments in the simplest of ways. The two different historical versions of echo vary in fatally incompatible ways.

> The BSD echo checks the first argument for the string -n which causes it to suppress the <newline> that would otherwise follow the final argument in the output.

> The System V echo does not support any options, but allows escape sequences within its operands, as described for XSI implementations in the OPERANDS section.

> The echo utility does not support Utility Syntax Guideline 10 because historical applications depend on echo to echo all of its arguments, except for the -n option in the BSD version.

#### FUTURE DIRECTIONS

> None.

#### SEE ALSO

> printf

#### CHANGE HISTORY

> First released in Issue 2.

#### Issue 5

> In the OPTIONS section, the last sentence is changed to indicate that implementations "do not" support any options; in the previous issue this said "need not".

#### Issue 6

> The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:

> - A set of character sequences is defined as string operands.

> - LC_CTYPE is added to the list of environment variables affecting echo.

> - In the OPTIONS section, implementations shall not support any options.

> IEEE Std 1003.1-2001/Cor 1-2002, item XCU/TC1/D6/21 is applied, so that the echo utility can accommodate historical BSD behavior.

End of informative text.

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