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ID Category Severity Type Date Submitted Last Update
0001272 [1003.1(2016)/Issue7+TC2] Shell and Utilities Objection Error 2019-07-24 20:34 2019-08-15 16:16
Reporter stephane View Status public  
Assigned To
Priority normal Resolution Accepted As Marked  
Status Resolved  
Name Stephane Chazelas
User Reference
Section colon special utility
Page Number 2388 (in 2018 edition)
Line Number
Interp Status ---
Final Accepted Text Note: 0004523
Summary 0001272: colon doesn't "expand its arguments" and must not process options
Description The colon special utility specification says:

> This utility shall only expand command arguments.

That is not true. ":" doesn't do anything with its arguments.

I beleive what that text meant was that ":" is a special builtin
as any other and not a comment introducing token in the shell
syntax contrary to "#", so that what follows is subject to all

For instance that in:

: "$((a = 1))" /*/*/*/*

Those arithmetic and pathname expansions and their side effects
are still performed before the ":" utility is invoked.

But what the ":" utility gets as arguments is the result of
those expansions, and it doesn't do anything with them.

Also, it says "OPTIONS: None". But that would still mean that
implementations are free to support some as extensions. Worse,
since ":" is a special builtin, that means that implementations
are not required to support "--" as an end-of-option marker.

Yet, as demonstrated in the (broken, see below) first example,
things like:

: "${X=abc}"

are a common idiom.

In the current version of the spec however, that produces
unspecified results unless $X can be guaranteed not to start
with a "-" (and : -- "${X=abc}" doesn't fix it).

I don't know of any shell implementation whose ":" handles
options. Even ksh93 where most builtins support common
--help/--man/--author options doesn't do it for ":".

POSIX should make it clear that no option processing should be
done, that all the arguments are to be ignored.

The first example:

> : ${X=abc}
> if false
> then :
> else echo $X
> fi

has a few poor shell coding practice instances/bugs:

- missing quotes around expansions
- usage of echo for arbitrary data
Desired Action Change the DESCRIPTION to:

This utility shall do nothing and return with a 0 exit status.

Change OPTIONS to:

The null utility shall not process any option. All arguments
shall be ignored whether they start with "-" or not.

If deemed necessary, add an "APPLICATION USAGE" section
clarifying that ":" differs from "#" in that it's a command and
not a token in the shell syntax. And that it differs from "true"
in that it's a special utility, accepts arguments that it
ignores and doesn't process options (that's also the case of
most true implementations but not all).

Change the first example to:

: "${X=abc}"
if     false
then   :
else   printf '%s\n' "$X"

On an unrelated note, as it's very unintuitive, it may be worth
also adding to the second example description as a reminder:
"colon being a special utility, if the z file cannot be opened,
it shall cause the shell to exit".
Tags tc3-2008
Attached Files

- Relationships

-  Notes
geoffclare (manager)
2019-08-15 16:15

On page 2389 line 76434 section 2.14 colon, change:
This utility shall only expand command arguments.
This utility shall do nothing except return a 0 exit status.

On page 2389 line 76437 section 2.14 colon, change OPTIONS from:
This utility shall not recognize the "--" argument in the manner specified by Guideline 10 of [xref to XBD 12.2]. Implementations shall not support any options.

On page 2389 line 76451 section 2.14 colon, change STDERR from:
The standard error shall be used only for diagnostic messages.
Not used.

On page 2389 line 76459 section 2.14 colon, change CONSEQUENCES OF ERRORS from:

On page 2389 line 76463 section 2.14 colon, change the first example to:
: "${X=abc}"
if     false
then   :
else   printf '%s\n' "$X"

On page 2390 line 76472 section 2.14 colon, change:
... and creates or truncates file z.
... and creates or truncates file z; if the file cannot be created or truncated, a non-interactive shell exits (see [xref to 2.8.1]).

- Issue History
Date Modified Username Field Change
2019-07-24 20:34 stephane New Issue
2019-07-24 20:34 stephane Name => Stephane Chazelas
2019-07-24 20:34 stephane Section => colon special utility
2019-07-24 20:34 stephane Page Number => 2388 (in 2018 edition)
2019-08-15 16:15 geoffclare Note Added: 0004523
2019-08-15 16:16 geoffclare Interp Status => ---
2019-08-15 16:16 geoffclare Final Accepted Text => Note: 0004523
2019-08-15 16:16 geoffclare Status New => Resolved
2019-08-15 16:16 geoffclare Resolution Open => Accepted As Marked
2019-08-15 16:16 geoffclare Tag Attached: tc3-2008

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