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Re: Issues with history substitution and its documentation


From: Jim Monte
Subject: Re: Issues with history substitution and its documentation
Date: Wed, 6 Nov 2019 08:04:12 -0500

Regarding the & word modifier, it would be useful to note in the
documentation that it applies the previous substitution whether it had been
successful or not, as shown below.

[root@localhost ~]# echo a
a
[root@localhost ~]# !:s/a/z/
echo z
z
[root@localhost ~]# echo a1
a1
[root@localhost ~]# !:&
echo z1
z1
[root@localhost ~]# echo a2
a2
[root@localhost ~]# !:s/b/y/
bash: :s/b/y/: substitution failed
[root@localhost ~]# echo b2
b2
[root@localhost ~]# !:&
echo y2
y2
[root@localhost ~]#


Jim

On Tue, Nov 5, 2019 at 11:44 AM Jim Monte <address@hidden> wrote:

> The availability of the % string only after a command unrelated to it (not
> using !??) is executed as shown below is not documented, but it probably
> falls under the category of a bug. That is, it seems reasonable that both
> echo "!%" commands should behave as the second one does.
> [root@localhost ~]# bash
> [root@localhost ~]# echo "!%"
> bash: !: event not found
> [root@localhost ~]# echo a >/dev/nul
> [root@localhost ~]# echo "!%"
> echo ""
>
> [root@localhost ~]#
>
> Jim
>
> On Mon, Nov 4, 2019 at 9:42 AM Jim Monte <address@hidden> wrote:
>
>> Related to the issues with the ? event designator, the %word designator
>> substitutes the *first* word  matched by the ? event designator or nothing
>> if the match begins with a space. These details are not documented.
>>
>> [root@localhost ~]# echo a b c d >/dev/nul
>> [root@localhost ~]# echo !?b c?
>> echo echo a b c d >/dev/nul
>> [root@localhost ~]# echo "!%"
>> echo "b"
>> b
>> [root@localhost ~]# echo a1 >/dev/nul
>> [root@localhost ~]# echo !? a?
>> echo echo a1 >/dev/nul
>> [root@localhost ~]# echo "!%"
>> echo ""
>>
>> Jim
>>
>>
>>
>>
>>
>> On Sun, Nov 3, 2019 at 9:18 AM Jim Monte <address@hidden> wrote:
>>
>>> Two more documentation issues I have found are below.
>>>
>>> It appears that an empty substring event designator uses the string of
>>> the previous substring event designator if none is provided and does not
>>> find the event if there is no previous string.
>>>
>>> [root@localhost ~]# ls
>>> dos      hello.c
>>> [root@localhost ~]# cat hello.c > /dev/nul
>>> [root@localhost ~]# echo !?s?
>>> echo ls
>>> ls
>>> [root@localhost ~]# echo !??
>>> echo echo ls
>>> echo ls
>>> [root@localhost ~]# ls -al > /dev/nul
>>> [root@localhost ~]# echo !??
>>> echo ls -al > /dev/nul
>>> [root@localhost ~]# echo s
>>> s
>>> [root@localhost ~]# echo !??
>>> echo echo s
>>> echo s
>>> [root@localhost ~]# echo !?l?
>>> echo echo ls -al > /dev/nul
>>> [root@localhost ~]# echo !??
>>> echo echo echo ls -al > /dev/nul
>>>
>>> [root@localhost ~]# bash
>>> [root@localhost ~]# echo !??
>>> bash: !??: event not found
>>>
>>> This action is not documented.
>>>
>>>
>>>
>>>
>>>
>>> An empty "old" string in a substitute word modifier uses the previous
>>> "old" if none is given, but uses an empty string if new is empty. If there
>>> was no previous "old" string, an error is reported.
>>>
>>> [root@localhost ~]# echo f g i
>>> f g i
>>> [root@localhost ~]# echo !:s/g/k/
>>> echo echo f k i
>>> echo f k i
>>> [root@localhost ~]# echo af ag ai
>>> af ag ai
>>> [root@localhost ~]# echo !:s///
>>> echo echo af a ai
>>> echo af a ai
>>> [root@localhost ~]# echo bf bg bi
>>> bf bg bi
>>> [root@localhost ~]# echo !:s//1/
>>> echo echo bf b1 bi
>>> echo bf b1 bi
>>> [root@localhost ~]# echo gf gg gi
>>> gf gg gi
>>> [root@localhost ~]# echo !:gs//2/
>>> echo echo 2f 22 2i
>>> echo 2f 22 2i
>>>
>>> [root@localhost ~]# bash
>>> [root@localhost ~]# echo a b c
>>> a b c
>>> [root@localhost ~]# echo !:s//1/
>>> bash: :s//1/: no previous substitution
>>>
>>> Again, this behavior is not documented.
>>>
>>> On Thu, Oct 10, 2019 at 10:35 PM Jim Monte <address@hidden>
>>> wrote:
>>>
>>>> Hi,
>>>>
>>>> This bug report has been my first one for Bash. I have not found how to
>>>> check the status of the bug. Would you please provide this information?
>>>>
>>>> Below are a couple more issues I found.
>>>>
>>>> There is an inconsistency with the documentation and behavior of the ^
>>>> word designator. According to documentation, it refers to the first
>>>> argument but does not require a ':' before it if it starts the word
>>>> designator. However, it does not act like the numerical word designator 1
>>>> at the end of a range.
>>>>
>>>> [root@localhost ~]# echo a b c
>>>> a b c
>>>> [root@localhost ~]# echo !!:1-1
>>>> echo a
>>>> a
>>>> [root@localhost ~]# echo a b c
>>>> a b c
>>>> [root@localhost ~]# echo !!:^-^
>>>> echo a b^
>>>> a b^
>>>>
>>>> Also it is not explicitly documented that :- is equivalent to :0-
>>>>
>>>> [root@localhost ~]# echo a b c d
>>>> a b c d
>>>> [root@localhost ~]# echo !!:-
>>>> echo echo a b c
>>>> echo a b c
>>>> [root@localhost ~]# echo a b c d
>>>> a b c d
>>>> [root@localhost ~]# echo !!:0-
>>>> echo echo a b c
>>>> echo a b c
>>>>
>>>>
>>>> Jim Monte
>>>>
>>>> On Thu, Oct 3, 2019 at 6:19 PM Jim Monte <address@hidden> wrote:
>>>>
>>>>> Hi All,
>>>>>
>>>>> Below are some issues I found with history substitution. I am
>>>>> duplicating its behavior in a somewhat different use, and found issues 
>>>>> with
>>>>> the documentation and bugs as described.
>>>>>
>>>>> Jim Monte
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> From: jim
>>>>> To: address@hidden
>>>>> Subject: Issues with history substitution and its documentation
>>>>>
>>>>> Configuration Information [Automatically generated, do not change]:
>>>>> Machine: x86_64
>>>>> OS: linux-gnu
>>>>> Compiler: gcc
>>>>> Compilation CFLAGS:  -DPROGRAM='bash' -DCONF_HOSTTYPE='x86_64'
>>>>> -DCONF_OSTYPE='l$
>>>>> uname output: Linux T5500-Ubuntu 4.18.0-22-generic #23~18.04.1-Ubuntu
>>>>> SMP Thu J$
>>>>> Machine Type: x86_64-pc-linux-gnu
>>>>>
>>>>> Bash Version: 4.4
>>>>> Patch Level: 19
>>>>> Release Status: release
>>>>>
>>>>> Description:
>>>>>
>>>>> =============================================================================
>>>>> Documentation of quick substitution is incorrect (or does not match
>>>>> behavior).
>>>>>
>>>>> I believe this issue is an error with the documentation of history
>>>>> "Quick Substitution" that has existed since the first snapshot
>>>>> available at
>>>>> web.archive.org in 2007 at
>>>>>
>>>>>
>>>>> https://web.archive.org/web/20071223174140/http://www.gnu.org/software/bash/manual/html_node/Event-Designators.html
>>>>>
>>>>> At the least it is true that bash does not behave as the documentation
>>>>> states,
>>>>> but it does act in a way that is more reasonable (to me) than what is
>>>>> written.
>>>>>
>>>>> The documentation states that ^string1^string2^ is equivalent to
>>>>> !!:s/string1/string2/. However, bash treats it as equivalent to
>>>>> !!:s^string1^string2^.
>>>>>
>>>>> jim@T5500-Ubuntu:~$ echo /a
>>>>> /a
>>>>> jim@T5500-Ubuntu:~$ ^/a^b^
>>>>> echo b
>>>>> b
>>>>> jim@T5500-Ubuntu:~$ echo /a
>>>>> /a
>>>>> jim@T5500-Ubuntu:~$ !!:s//a/b/
>>>>> echo ab/
>>>>> ab/
>>>>> jim@T5500-Ubuntu:~$ echo /a
>>>>> /a
>>>>> jim@T5500-Ubuntu:~$ !!:s^/a^b^
>>>>> echo b
>>>>> b
>>>>>
>>>>>
>>>>> =============================================================================
>>>>> Behavior of empty "old" string in a substitution is undefined.
>>>>>
>>>>> The earlier example also shows a related but different issue with the
>>>>> !!:s//a/b/ command, where the string to locate is empty.
>>>>> It causes /a to be replaced by a and the b/ is appended.
>>>>>
>>>>> But
>>>>> jim@T5500-Ubuntu:~$ echo ///a
>>>>> ///a
>>>>> jim@T5500-Ubuntu:~$ !!:s//z/
>>>>> echo //z
>>>>> //z
>>>>>
>>>>> Here the empty string caused /a to be replaced by z.
>>>>>
>>>>> However,
>>>>> jim@T5500-Ubuntu:~$ echo ///abcdefg
>>>>> ///abcdefg
>>>>> jim@T5500-Ubuntu:~$ !!:s//z/
>>>>> echo //zbcdefg
>>>>> //zbcdefg
>>>>>
>>>>> Here a slash and the first character of the second word are replaced
>>>>> by z.
>>>>>
>>>>>
>>>>> jim@T5500-Ubuntu:~$ echo a b c
>>>>> a b c
>>>>> jim@T5500-Ubuntu:~$ !!:s//z/
>>>>> echo z b c
>>>>> z b c
>>>>>
>>>>>
>>>>> jim@T5500-Ubuntu:~$ echo ///
>>>>> ///
>>>>> jim@T5500-Ubuntu:~$ !!:s//z/
>>>>> bash: :s//z/: substitution failed
>>>>>
>>>>> Using :gs instead of :s does not change the results.
>>>>>
>>>>>
>>>>> =============================================================================
>>>>> BUG
>>>>> If an event designator has a leading - character, it is ignored.
>>>>>
>>>>> jim@T5500-Ubuntu:~/tmp$ cat main.c
>>>>> #include <stdio.h>
>>>>> int main(void)
>>>>> {
>>>>>     (void) fprintf(stdout, "Hello, world!\n");
>>>>>     return 0;
>>>>> }
>>>>>
>>>>> jim@T5500-Ubuntu:~/tmp$ gcc main.c -o"-a"
>>>>> jim@T5500-Ubuntu:~/tmp$ gcc main.c -o"-b"
>>>>> jim@T5500-Ubuntu:~/tmp$ -a
>>>>> Hello, world!
>>>>> jim@T5500-Ubuntu:~/tmp$ !-a:s/a/b
>>>>> bpt-cache abc
>>>>>
>>>>>
>>>>>
>>>>> =============================================================================
>>>>> Documentation of the :h and :t modifiers in section 9.3.3 is
>>>>> incomplete.
>>>>> :h removes the last / and everything after it if a / is present.
>>>>> Otherwise
>>>>> it does nothing.
>>>>>
>>>>> :t removes everything before and including the last / if one is
>>>>> present.
>>>>> Otherwise it does nothing.
>>>>>
>>>>> If a slash is present, !!:h/!!:t is equivalent to !!.
>>>>>
>>>>> jim@T5500-Ubuntu:~$ echo /a/b/c/d
>>>>> /a/b/c/d
>>>>> jim@T5500-Ubuntu:~$ !!:h
>>>>> echo /a/b/c
>>>>> /a/b/c
>>>>> jim@T5500-Ubuntu:~$ echo /a/b/c/d
>>>>> /a/b/c/d
>>>>> jim@T5500-Ubuntu:~$ !!:h:h
>>>>> echo /a/b
>>>>> /a/b
>>>>> jim@T5500-Ubuntu:~$ echo /a/b/c/d
>>>>> /a/b/c/d
>>>>> jim@T5500-Ubuntu:~$ !!:h:h:h
>>>>> echo /a
>>>>> /a
>>>>> jim@T5500-Ubuntu:~$ echo /a/b/c/d
>>>>> /a/b/c/d
>>>>> jim@T5500-Ubuntu:~$ !!:h:h:h:h
>>>>> echo
>>>>>
>>>>> jim@T5500-Ubuntu:~$
>>>>> jim@T5500-Ubuntu:~$ echo /a/b/c/d
>>>>> /a/b/c/d
>>>>> jim@T5500-Ubuntu:~$ !!:t
>>>>> d
>>>>> d: command not found
>>>>>
>>>>>
>>>>> jim@T5500-Ubuntu:~$ echo a/b
>>>>> a/b
>>>>> jim@T5500-Ubuntu:~$ !!:h/!!:t
>>>>> echo a/b
>>>>> a/b
>>>>> jim@T5500-Ubuntu:~$ echo a/b
>>>>> a/b
>>>>> jim@T5500-Ubuntu:~$ !!
>>>>> echo a/b
>>>>> a/b
>>>>>
>>>>>
>>>>>
>>>>> =============================================================================
>>>>> Documentation of the :r and :e modifiers is incomplete.
>>>>> :r removes the last ".suffix" and everything after it, if a ".suffix"
>>>>> is
>>>>> present. Otherwise it does nothing.
>>>>> :e leaves the last ".suffix" and everything after it, if a ".suffix" is
>>>>> present. Otherwise it does nothing.
>>>>>
>>>>> jim@T5500-Ubuntu:~$ echo .suffix a b .suffix c d
>>>>> .suffix a b .suffix c d
>>>>> jim@T5500-Ubuntu:~$ !!:r
>>>>> echo .suffix a b
>>>>> .suffix a b
>>>>> jim@T5500-Ubuntu:~$ echo .suffix a b .suffix c d
>>>>> .suffix a b .suffix c d
>>>>> jim@T5500-Ubuntu:~$ !!:r:r
>>>>> echo
>>>>>
>>>>> jim@T5500-Ubuntu:~$ echo .suffix a b  .suffix c d
>>>>> .suffix a b .suffix c d
>>>>> jim@T5500-Ubuntu:~$ !!:e
>>>>> .suffix c d
>>>>>
>>>>> jim@T5500-Ubuntu:~$ echo a b c
>>>>> a b c
>>>>> jim@T5500-Ubuntu:~$ !!:r
>>>>> echo a b c
>>>>> a b c
>>>>> jim@T5500-Ubuntu:~$ echo a b c
>>>>> a b c
>>>>> jim@T5500-Ubuntu:~$ !!:e
>>>>> echo a b c
>>>>> a b c
>>>>>
>>>>>
>>>>> =============================================================================
>>>>> BUG
>>>>> :p does not suppress execution if it is duplicated.
>>>>>
>>>>> jim@T5500-Ubuntu:~$ echo a b c
>>>>> a b c
>>>>> jim@T5500-Ubuntu:~$ !!:p
>>>>> echo a b c
>>>>> jim@T5500-Ubuntu:~$ echo a b c
>>>>> a b c
>>>>> jim@T5500-Ubuntu:~$ !!:p:p
>>>>> echo a b c
>>>>> a b c
>>>>>
>>>>>
>>>>> =============================================================================
>>>>> Documentation of :q and :x is incomplete.
>>>>> If :q and :x are repeated, the last specification is taken.
>>>>>
>>>>> jim@T5500-Ubuntu:~$ echo a b c
>>>>> a b c
>>>>> jim@T5500-Ubuntu:~$ !!:q
>>>>> 'echo a b c'
>>>>> echo a b c: command not found
>>>>> jim@T5500-Ubuntu:~$ echo a b c
>>>>> a b c
>>>>> jim@T5500-Ubuntu:~$ !!:x
>>>>> 'echo' 'a' 'b' 'c'
>>>>> a b c
>>>>> jim@T5500-Ubuntu:~$ echo a b c
>>>>> a b c
>>>>> jim@T5500-Ubuntu:~$ !!:q:x
>>>>> 'echo' 'a' 'b' 'c'
>>>>> a b c
>>>>> jim@T5500-Ubuntu:~$ echo a b c
>>>>> a b c
>>>>> jim@T5500-Ubuntu:~$ !!:q:x:q
>>>>> 'echo a b c'
>>>>> echo a b c: command not found
>>>>> jim@T5500-Ubuntu:~$ echo a b c
>>>>> a b c
>>>>> jim@T5500-Ubuntu:~$ !!:q:x:q:x
>>>>> 'echo' 'a' 'b' 'c'
>>>>> a b c
>>>>>
>>>>>
>>>>>  
>>>>> =============================================================================
>>>>> Finally, documentation of G should mention that it can be used with
>>>>> both :s and &.
>>>>>
>>>>>
>>>>>


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