Re: How to enter escape character in a positional string argument from the command line?

[Chris Angelico]

On Thu, 22 Dec 2022 at 03:11, Stefan Ram  wrote:
>
> Lars Liedtke  writes:
> >Or you could have "native" bash ($SHELL) with WSL.
>
>   In this newsgroup, it would actually be obvious to use Python.

Less obvious than you might think - partly because bash is just so
dang good that it's really really hard to outdo it :) Sure, bash has a
lot of weird and wonky edge cases, but it's an incredibly practical
shell to use.

>   When commands are typed manually, this might be a bit verbose,
>   though. I mean
>
> os.chdir( r'C:\EXAMPLE' )
>
>   versus
>
> CD C:\EXAMPLE

Exactly. What's good for a programming language is often not good for a shell.

> class PythonShell( cmd.Cmd ):
>
> intro = 'Welcome to the Python shell. Type help or ? to list commands.\n'
> prompt = '(Python) '
> file = None
>
> def do_cd( self, arg ):
> 'change directory:  CD C:\EXAMPLE'
> os.chdir( *parse( arg ))
>
> def do_bye( self, arg ):
> 'Exit:  BYE'
> print( 'Thank you for using the Python Shell!' )
> return True

Sure, you can always create your own shell. But I think you'll find
that, as you start expanding on this, you'll end up leaning more
towards "implementing bash-like and/or cmd-like semantics in Python"
rather than "creating a Python shell". Shells, in general, try to
execute programs as easily and conveniently as possible. Programming
languages try to stay inside themselves and do things, with subprocess
spawning being a much less important task.

Fun challenge: see how much you can do in bash without ever forking to
another program. And by "fun", I mean extremely difficult, and by
"challenge" I really mean "something you might have to do when your
system is utterly hosed and all you have available is one root shell".

It's amazing how far you can go when your hard drive has crashed and
you desperately need to get one crucial login key that you thought you
had saved elsewhere but hadn't.

ChrisA
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Re: How to enter escape character in a positional string argument from the command line?

[Chris Angelico]

On Thu, 22 Dec 2022 at 03:11, Jach Feng  wrote:
>
> Chris Angelico 在 2022年12月21日 星期三下午1:02:01 [UTC+8] 的信中寫道：
> > On Wed, 21 Dec 2022 at 15:28, Jach Feng  wrote:
> > > That's what I am taking this path under Windows now, the ultimate 
> > > solution before Windows has shell similar to bash:-)
> > Technically, Windows DOES have a shell similar to bash. It's called
> > bash. :) The trouble is, most people use cmd.exe instead.
> >
> > ChrisA
> Really? Where? I can't find it in my Windows 8.1

Ah, I didn't mean "ships with"; bash for Windows is very much
available, but you'd have to go fetch it. Try the Windows app store
first, and if not, a quick web search will find it. Or install Git for
Windows, which comes with bash.

ChrisA
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Re: How to enter escape character in a positional string argument from the command line?

[Jach Feng]

Chris Angelico 在 2022年12月21日 星期三下午1:02:01 [UTC+8] 的信中寫道：
> On Wed, 21 Dec 2022 at 15:28, Jach Feng  wrote: 
> > That's what I am taking this path under Windows now, the ultimate solution 
> > before Windows has shell similar to bash:-)
> Technically, Windows DOES have a shell similar to bash. It's called 
> bash. :) The trouble is, most people use cmd.exe instead. 
> 
> ChrisA
Really? Where? I can't find it in my Windows 8.1
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Re: How to enter escape character in a positional string argument from the command line?

[Chris Angelico]

On Wed, 21 Dec 2022 at 23:16, Albert-Jan Roskam  wrote:
>
>
>
> On Dec 21, 2022 06:01, Chris Angelico  wrote:
>
> On Wed, 21 Dec 2022 at 15:28, Jach Feng  wrote:
> > That's what I am taking this path under Windows now, the ultimate solution 
> > before Windows has shell similar to bash:-)
>
> Technically, Windows DOES have a shell similar to bash. It's called
> bash. :) The trouble is, most people use cmd.exe instead.
>
>
> =
>
> I use Git Bash quite a lot: https://gitforwindows.org/
>
> Is that the one you're referring to?
>

Yeah, that's probably the easiest way to get hold of it.

ChrisA
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Re: How to enter escape character in a positional string argument from the command line?

[Lars Liedtke]

Or you could have "native" bash ($SHELL) with WSL. But I assume not everyone is 
using it.

Cheers

Lars


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Am 21.12.22 um 13:15 schrieb Albert-Jan Roskam:

  On Dec 21, 2022 06:01, Chris Angelico 
 wrote:

On Wed, 21 Dec 2022 at 15:28, Jach Feng 
 wrote:
> That's what I am taking this path under Windows now, the ultimate
solution before Windows has shell similar to bash:-)

Technically, Windows DOES have a shell similar to bash. It's called
bash. :) The trouble is, most people use cmd.exe instead.

  =
  I use Git Bash quite a lot: https://gitforwindows.org/
  Is that the one you're referring to?

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Re: How to enter escape character in a positional string argument from the command line?

[Albert-Jan Roskam]

   On Dec 21, 2022 06:01, Chris Angelico  wrote:

 On Wed, 21 Dec 2022 at 15:28, Jach Feng  wrote:
 > That's what I am taking this path under Windows now, the ultimate
 solution before Windows has shell similar to bash:-)

 Technically, Windows DOES have a shell similar to bash. It's called
 bash. :) The trouble is, most people use cmd.exe instead.

   =
   I use Git Bash quite a lot: https://gitforwindows.org/
   Is that the one you're referring to?
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Re: How to enter escape character in a positional string argument from the command line?

[Chris Angelico]

On Wed, 21 Dec 2022 at 15:28, Jach Feng  wrote:
> That's what I am taking this path under Windows now, the ultimate solution 
> before Windows has shell similar to bash:-)

Technically, Windows DOES have a shell similar to bash. It's called
bash. :) The trouble is, most people use cmd.exe instead.

ChrisA
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Re: How to enter escape character in a positional string argument from the command line?

[Jach Feng]

ery...@gmail.com 在 2022年12月20日 星期二中午12:35:52 [UTC+8] 的信中寫道：
> On 12/19/22, Jach Feng  wrote: 
> > 
> > That's really good for Linux user! How about Windows?
> In CMD, typing the "^" escape character at the end of a line ignores 
> the newline and prompts for "more" input. If you press enter again, 
> you'll get another "more" prompt in which you can write the rest of 
> the command line. Command-line arguments are separated by spaces, so 
> you have to start the next line with a space if you want it to be a 
> new argument. Also, "^" is a literal character when it's in a 
> double-quoted string, which requires careful use of quotes. For 
> example: 
> 
> C:\>py -c "import sys; print(sys.orig_argv[3:])" spam^ 
> More? 
> More? eggs^ 
> More? 
> More? " and spam" 
> ['spam\n', 'eggs\n and spam'] 
> 
> The above is easier in PowerShell, which supports entering multiline 
> strings without having to escape the newline. The second-level prompt 
> is ">> ". For example: 
> 
> > py -c "import sys; print(sys.orig_argv[3:])" spam" 
> >> " eggs" 
> >> and spam" 
> ['spam\n', 'eggs\n and spam']
Thanks for the information. No idea Windows CMD can take such a trick to enter 
"\n" :-)
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Re: How to enter escape character in a positional string argument from the command line?

[Jach Feng]

Thomas Passin 在 2022年12月20日 星期二上午11:36:41 [UTC+8] 的信中寫道：
> On 12/19/2022 9:24 PM, Jach Feng wrote: 
> > Mark Bourne 在 2022年12月20日 星期二凌晨4:49:13 [UTC+8] 的信中寫道： 
> >> Jach Feng wrote: 
> >>> I have a script using the argparse module. I want to enter the string 
> >>> "step\x0A" as one of its positional arguments. I expect this string has a 
> >>> length of 5, but it gives 8. Obviously the escape character didn't 
> >>> function correctly. How to do it? 
> >> That depends on the command-line shell you're calling your script from. 
> >> 
> >> In bash, you can include a newline in a quoted string: 
> >> ./your_script 'step 
> >> ' 
> >> (the closing quote is on the next line) 
> >> 
> >> Or if you want to do it on a single line (or use other escape 
> >> sequences), you can use e.g.: 
> >> ./your_script $'step\x0a' 
> >> (dollar sign before a single-quoted string which contains escape 
> >> sequences) 
> >> 
> >> -- 
> >> Mark. 
> > That's really good for Linux user! How about Windows?
> One way is to process the argument after it gets into Python rather than 
> before. How hard that will be depends on how general you need the 
> argument to be. For your actual example, the argument comes into Python 
> as if it were 
> 
> arg1 = r"step\x0A" # or "step\\x0a" 
> 
> You can see if there is an "\\x": 
> 
> pos = arg1.find('\\x') # 4 
> 
> Replace or use a regex to replace it: 
> 
> arg1_fixed = arg1.replace('\\x0A', '\n') 
> 
> Naturally, if "\\x0A" is only a special case and other combinations are 
> possible, you will need to figure out what you need and do some more 
> complicated processing.
That's what I am taking this path under Windows now, the ultimate solution 
before Windows has shell similar to bash:-)
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Re: How to enter escape character in a positional string argument from the command line?

[Eryk Sun]

On 12/19/22, Jach Feng  wrote:
>
> That's really good for Linux user! How about Windows?

In CMD, typing the "^" escape character at the end of a line ignores
the newline and prompts for "more" input. If you press enter again,
you'll get another "more" prompt in which you can write the rest of
the command line. Command-line arguments are separated by spaces, so
you have to start the next line with a space if you want it to be a
new argument. Also, "^" is a literal character when it's in a
double-quoted string, which requires careful use of quotes. For
example:

C:\>py -c "import sys; print(sys.orig_argv[3:])" spam^
More?
More?  eggs^
More?
More? " and spam"
['spam\n', 'eggs\n and spam']

The above is easier in PowerShell, which supports entering multiline
strings without having to escape the newline. The second-level prompt
is ">> ". For example:

> py -c "import sys; print(sys.orig_argv[3:])" spam"
>> " eggs"
>>  and spam"
['spam\n', 'eggs\n and spam']
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Re: How to enter escape character in a positional string argument from the command line?

[Thomas Passin]

On 12/19/2022 9:24 PM, Jach Feng wrote:

Mark Bourne 在 2022年12月20日 星期二凌晨4:49:13 [UTC+8] 的信中寫道：

Jach Feng wrote:

I have a script using the argparse module. I want to enter the string 
"step\x0A" as one of its positional arguments. I expect this string has a 
length of 5, but it gives 8. Obviously the escape character didn't function correctly. 
How to do it?

That depends on the command-line shell you're calling your script from.

In bash, you can include a newline in a quoted string:
./your_script 'step
'
(the closing quote is on the next line)

Or if you want to do it on a single line (or use other escape
sequences), you can use e.g.:
./your_script $'step\x0a'
(dollar sign before a single-quoted string which contains escape sequences)

--
Mark.

That's really good for Linux user! How about Windows?


One way is to process the argument after it gets into Python rather than 
before. How hard that will be depends on how general you need the 
argument to be.  For your actual example, the argument comes into Python 
as if it were


arg1 = r"step\x0A"  # or "step\\x0a"

You can see if there is an "\\x":

pos = arg1.find('\\x')  # 4

Replace or use a regex to replace it:

arg1_fixed = arg1.replace('\\x0A', '\n')

Naturally, if "\\x0A" is only a special case and other combinations are 
possible, you will need to figure out what you need and do some more 
complicated processing.


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Re: How to enter escape character in a positional string argument from the command line?

[Jach Feng]

Mark Bourne 在 2022年12月20日 星期二凌晨4:49:13 [UTC+8] 的信中寫道：
> Jach Feng wrote: 
> > I have a script using the argparse module. I want to enter the string 
> > "step\x0A" as one of its positional arguments. I expect this string has a 
> > length of 5, but it gives 8. Obviously the escape character didn't function 
> > correctly. How to do it?
> That depends on the command-line shell you're calling your script from. 
> 
> In bash, you can include a newline in a quoted string: 
> ./your_script 'step 
> ' 
> (the closing quote is on the next line) 
> 
> Or if you want to do it on a single line (or use other escape 
> sequences), you can use e.g.: 
> ./your_script $'step\x0a' 
> (dollar sign before a single-quoted string which contains escape sequences) 
> 
> -- 
> Mark.
That's really good for Linux user! How about Windows?
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Re: How to enter escape character in a positional string argument from the command line?

[Mark Bourne]

Jach Feng wrote:

I have a script using the argparse module. I want to enter the string 
"step\x0A" as one of its positional arguments. I expect this string has a 
length of 5, but it gives 8. Obviously the escape character didn't function correctly. 
How to do it?


That depends on the command-line shell you're calling your script from.

In bash, you can include a newline in a quoted string:
./your_script 'step
'
(the closing quote is on the next line)

Or if you want to do it on a single line (or use other escape 
sequences), you can use e.g.:

./your_script $'step\x0a'
(dollar sign before a single-quoted string which contains escape sequences)

--
Mark.
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