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From: Jim Monte <jim.monte01@gmail.com>
Newsgroups: gnu.bash.bug
Subject: Issues with history substitution and its documentation
Date: Thu, 3 Oct 2019 18:19:49 -0400
Lines: 255
Approved: bug-bash@gnu.org
Message-ID: <mailman.932.1570163391.2651.bug-bash@gnu.org>
References: <CA+VKLw-WX8zUz06MZ9ThuMhUuW97aJ5ted8oSfJSvrVJBLW3hA@mail.gmail.com>
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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: bug-bash@gnu.org
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 &.