Subject: Re: echo semantics (was ksh need help!)
To: NetBSD User's Discussion List <netbsd-users@NetBSD.ORG>
From: Greg A. Woods <>
List: netbsd-users
Date: 12/20/2001 17:06:04
[ On Thursday, December 20, 2001 at 12:34:35 (-0000), David Laight wrote: ]
> Subject: Re: echo semantics (was ksh need help!)
> There is no 'print' in bourne shell (I've just checked under solaris)

No, and there's not supposed to be, though you can find it in a shell on

That's why Sun supply the XPG4 commands.  /usr/xpg4/bin/sh is supposed
to be a POSIX compliant/compatible shell and it does at least have a
(built-in) 'print' command.  Note that /usr/xpg4/bin/sh happens to be a
link to ../../bin/ksh, and even though the version of ksh in most
distributions of Solaris I've looked at isn't entirely 100% POSIX
compliant.  (If I'm not mistaken the XPG4 specifications became The
Single UNIX Specification (version 1?) in the change-over of X/Open to
The Open Group.  XPG4 was a "brand" trademark used to advertise
compliance with X/Open's specifications, and with the coming of SuSv2
the "brand" trademark changes to "UNIX 98")

NetBSD's implementation of echo, at least as far as the /bin/echo and
/bin/sh built-in are concerned, appears to be P1003.2 compliant in every
way, just as echo(1) claims.  No doubt the same applies for printf(1).

P1003.2 (at least as of Draft 12, the last publicly available version),
sanely defines a rather more restricted version of 'echo' than SuSv2.
(SuSv2 frequently strays beyond POSIX, often in what appear to be unwise
ways, but that was always the case with X/Open too.)

 4.19  echo - Write arguments to standard output

 4.19.1  Synopsis

 echo  [string ...]

 4.19.2  Description

 The echo utility shall write its arguments to standard output, followed
 by a <newline> character.  If there are no arguments, only the <newline>
 character shall be written.

 4.19.3  Options

 The echo utility shall not recognize the -- argument in the manner
 specified by utility syntax guideline 10 in 2.10.2; -- shall be
 recognized as a string operand.

 Implementations need not support any options.

 4.19.4  Operands

 The following operands shall be supported by the implementation:

    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

 4.19.5  External Influences  Standard Input

 None.  Input Files

 None.  Environment Variables

 The following environment variables shall affect the execution of echo:

    LANG               This variable shall determine the locale to use for
                       the locale categories when both LC_ALL and the
                       corresponding environment variable (beginning with
                       LC_) do not specify a locale.  See 2.6.

    LC_ALL             This variable shall determine the locale to be used
                       to override any values for locale categories
                       specified by the settings of LANG or any
                       environment variables beginning with LC_.

    LC_MESSAGES        This variable shall determine the language in which
                       diagnostic messages should be written.  Asynchronous Events


 4.19.6  External Effects  Standard Output

 The echo utility arguments shall be separated by single <space>s and a
 <newline> character shall follow the last argument.  Standard Error

 Used only for diagnostic messages.  Output Files


 4.19.7  Extended Description


 4.19.8  Exit Status

 The echo utility shall exit with one of the following values:

     0    Successful completion.

    >0    An error occurred.

 4.19.9  Consequences of Errors



 4.19.10  Rationale. (This subclause is not a part of P1003.2)


 As specified by this standard, echo writes its arguments in the simplest
 of ways.  The two different historical versions of echo vary in fatal
 incompatible ways.

 The BSD echo checks the first argument for the string "-n", which causes
 it to suppress the <newline> character 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:

    \a    Write an <alert> character.
    \b    Write a <backspace> character.

    \c    Suppress the <newline> character that otherwise follows the
          final argument in the output.  All characters following the \c
          in the arguments are ignored.

    \f    Write a <form-feed> character.

    \n    Write a <newline> character.

    \r    Write a <carriage-return> character.

    \t    Write a <tab> character.

    \v    Write a <vertical-tab> character.

    \\    Write a backslash character.

          Write an 8-bit value that is the 1-, 2-, or 3-digit octal number

 It is not possible to use echo portably across these two implementations
 unless both -n (as the first argument) and escape sequences are omitted.

 The printf utility (see 4.50) can be used to portably emulate any of the
 traditional behaviors of the echo utility as follows:

     - The System V echo is equivalent to:

             printf "%b\n" "$*"

     - The BSD echo is equivalent to:

             if [ "X$1" = "X-n" ]
                     printf "%s" "$*"
                     printf "%s\n" "$*"

 The echo utility does not support utility syntax guideline 10 because
 existing applications depend on echo to echo all of its arguments, except
 for the -n option in the BSD version.

 New applications are encouraged to use printf instead of echo.  The echo
 utility has not been made obsolescent because of its extremely widespread
 use in existing applications.


 In Draft 8, an attempt was made to merge the extensions of BSD and
 System V, supporting both -n and escape sequences.  During initial ballot
 resolution, a -e option was proposed to enable the escape conventions.
 Both attempts failed, as there are historical scripts that would be
 broken by any attempt at reconciliation.  Therefore, in Draft 9 only the
 simplest version of echo is presented.  Implementation-defined extensions
 on BSD and System V will keep historical applications content.  Portable
 applications that wish to do prompting without <newline>s or that could
 possibly be expecting to echo a "-n", should use the new printf utility
 (see 4.50), derived from the Ninth Edition.

 The LC_CTYPE variable is not cited because echo, as specified here, does
 not need to understand the characters in its arguments.  The System V and
 BSD implementations might need to be sensitive to it because of their


               Copyright c 1991 IEEE.  All rights reserved.
      This is an unapproved IEEE Standards Draft, subject to change.

 P1003.2/D11.2                               INFORMATION TECHNOLOGY--POSIX

P1003.2 obviously also defines printf, and gives the following reason
for doing so:

 4.50.10  Rationale. (This subclause is not a part of P1003.2)



 The printf utility was added to provide functionality that has
 historically been provided by echo.  However, due to irreconcilable
 differences in the various versions of echo extant, the version in this
 standard has few special features, leaving those to this new printf
 utility, which is based on one in the Ninth Edition at AT&T Bell Labs.

Also note this from P1003.2:

     (6)  When irreconcilable differences arose between versions of
          historical utilities, new interfaces (utility names or syntax)
          were sometimes added in their places.  The working group
          resisted the urge to deviate significantly from historical
          practice; the new interfaces are generally consistent with the
          philosophy of historical systems and represent comparable
          functionality to the interfaces being replaced.  In some cases,
          System V and BSD had diverged (such as with echo and sum) so
          significantly that no compromises for a common interface were
          possible.  In these cases, either the divergent features were
          omitted or an entirely new command name was selected (such as
          with printf and cksum).

								Greg A. Woods

+1 416 218-0098;  <>;  <>;  <>
Planix, Inc. <>; VE3TCP; Secrets of the Weird <>