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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 10:21:32 -0500

Another documentation issue for :s, and a bug, or two bugs, although it
seems to be one of each. Instead of "Any delimiter may be used in place of
‘/’.", it should be clarified that any character may be used in place of
'/' as a delimiter, although if '&' is used, it looses its special property
of being the value of old when it appears in new and if '\' is used, it
looses is ability to escape '&'. However, there is still an issue with an
escape being lost in some cases.

[root@localhost ~]# echo a b c
a b c
[root@localhost ~]# echo "!:s&b&\\\&&&"
echo "echo a \& c&"                              ******************* one
less '\' escape
echo a \& c&
[root@localhost ~]# echo a b c
a b c
[root@localhost ~]# echo "!:s/b/\\\&&/"
echo "echo a \\&b c"                             *******************
echo a \&b c
[root@localhost ~]# echo a b c
a b c
[root@localhost ~]# echo "!:szbz\\\&&z"
echo "echo a \\&b c"                             *******************
echo a \&b c

[root@localhost ~]# echo a b c
a b c
[root@localhost ~]# echo "!:s\b\\\\&&\"
echo "echo a  c\\&&\"
> "
echo a  c\&&"

[root@localhost ~]# echo a b c
a b c
[root@localhost ~]# echo "!:s\b\z\&&y\"
echo "echo a z c&&y\"
> "
echo a z c&&y"


Jim

On Wed, Nov 6, 2019 at 8:04 AM Jim Monte <address@hidden> wrote:

> 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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