View Issue Details
| ID | Project | Category | View Status | Date Submitted | Last Update |
|---|---|---|---|---|---|
| 0001272 | 1003.1(2016/18)/Issue7+TC2 | Shell and Utilities | public | 2019-07-24 20:34 | 2024-06-11 09:08 |
| Reporter | stephane | Assigned To | |||
| Priority | normal | Severity | Objection | Type | Error |
| Status | Closed | Resolution | Accepted As Marked | ||
| Name | Stephane Chazelas | ||||
| Organization | |||||
| User Reference | |||||
| Section | colon special utility | ||||
| Page Number | 2388 (in 2018 edition) | ||||
| Line Number | |||||
| Interp Status | --- | ||||
| Final Accepted Text | 0001272:0004523 | ||||
| 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 expansions. 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"
fi
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 | ||||
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On page 2389 line 76434 section 2.14 colon, change:This utility shall only expand command arguments.to: This utility shall do nothing except return a 0 exit status. On page 2389 line 76437 section 2.14 colon, change OPTIONS from: None.to: 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.to: Not used. On page 2389 line 76459 section 2.14 colon, change CONSEQUENCES OF ERRORS from: Default.to: None. On page 2389 line 76463 section 2.14 colon, change the first example to: On page 2390 line 76472 section 2.14 colon, change: ... and creates or truncates file z.to: ... 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]). |
| 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 | => 0001272:0004523 |
| 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 | |
| 2019-11-20 16:15 | geoffclare | Status | Resolved => Applied |
| 2024-06-11 09:08 | agadmin | Status | Applied => Closed |
