On Thu, 22 Dec 2022 at 03:58, gene heskett <gheskett@shentel.net> wrote:

On 12/21/22 11:22, Chris Angelico wrote:

On Thu, 22 Dec 2022 at 03:11, Stefan Ram <ram@zedat.fu-berlin.de> wrote:

Lars Liedtke <lal@solute.de> 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 you make a statement like that, Chris, you should also note that
every single one of those "wonky edge cases" is documented down to the
last dotted i. Bash's docs will kill a good sized pulp tree, needing
around a ream of paper to print on a duplex printer. I know, I did it
around a decade ago. If you like to write scripts, having a dead tree
copy of the docs at your elbow in incredibly useful. That huge man page
does not cover it like the printed docs do.

Oh yes, absolutely true. Its wonkiness is dependable and consistent;
but it is definitely quirky (look at all the different ways to embed
arguments into things, and the ways that $*, $@, "$*, and "$@" behave
when put into variables). Not usually a problem, but it does sometimes
leave you thinking "wow, wouldn't it be easier to just use something
like Python?". And in the complicated cases, yeah, it can be. But in
the simple cases? Bash rocks.

ChrisA

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On 12/21/22 11:22, Chris Angelico wrote:

On Thu, 22 Dec 2022 at 03:11, Stefan Ram <ram@zedat.fu-berlin.de> wrote:

Lars Liedtke <lal@solute.de> 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 you make a statement like that, Chris, you should also note that
every single one of those "wonky edge cases" is documented down to the
last dotted i. Bash's docs will kill a good sized pulp tree, needing
around a ream of paper to print on a duplex printer. I know, I did it
around a decade ago. If you like to write scripts, having a dead tree
copy of the docs at your elbow in incredibly useful. That huge man page
does not cover it like the printed docs do.

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

Cheers, Gene Heskett.
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
Genes Web page <http://geneslinuxbox.net:6309/>

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On Thu, 22 Dec 2022 at 04:12, Barry <barry@barrys-emacs.org> wrote:

I see bash scripts that are 1000’s of line of code at work and its a maintenance nightmare.

Knowing when to make the move from “handy bash script” to “this is a production application” and needs to be python is what I see people miss.

After a certain point in complexity the python code wins on maintenance. Personally i set a low bar to move from bash to python.

Agreed 100%. However, how many commands do you type a day at the bash
prompt? *Every one of those* is a simple case that doesn't need
Python. That's what makes bash such a great shell. You can type
simple, convenient commands, and they *just work*. Need something a
bit more complicated? You can do that too. Want to automate a short
sequence of commands? Don't have to translate them into another system
(like Python subprocess calls), just copy/paste them into a shell
script.

Yes, there absolutely is a point beyond which it's better to translate everything. But the vast number of commands executed every day? Most
of them are fine with bash. And that's why Python will never replace
bash as a shell.

ChrisA

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gene heskett <gheskett@shentel.net> writes:

When you make a statement like that, Chris, you should also note that
every single one of those "wonky edge cases" is documented down to the
last dotted i.

The Windows' cmd is wonky too, but not well documented.
For one example: The circumflex "^" can continue a command line.
But when one wants to use a literal circumflex "^" in a cmd
file or in a file name, it has to be escaped in ways that
seem to be quite irregular. This has been documented by
amateurs, but not by Microsoft AFAIK. (Search for "Note that
the phases described below are only a model of how the batch
parser works.".)

Here's a Windows cmd command file I wrote:

ffmpeg -i "source^^.mp4" ^
"target^^^^.mkv"

. The actual source and target file names are supposed to be
"source^^.mp4" and "target^^.mkv", but in the line continuation,
the "^" has to be escaped, while in the first line it has not!

(Ffmpeg is another piece of software with quite complex options.)

The following Windows cmd file creates three files "aa.txt",
"a^a.txt" and "a^^a.txt" with a delay of one minute between
each creation. Then it loops through the directory and prints
some stats about the files. All the fuss with the "SET" command
is only necessary to correctly iterate through files in a
directory in the presence of the possibility that file names
may contain the circumflex "^"! (Warning: The script will
overwrite some files in the directory it is executed in as
indicated by the use of ">" below". The file has been edited
in the newsreader before posting it and was not tested again
after that editing took place.)

echo 11111>aa.txt
timeout 62
echo 222222>a^^a.txt
timeout 62
echo 3333333>a^^^^a.txt

dir *.txt

setlocal enabledelayedexpansion
for /f %%i in ('dir /b *.txt') do (
SET "a=%%i"
SET "b=!a:^=^^!"
call :sub !b!
)
goto :eof

:sub
SET "A=%1"
SET "B=%1"
SET "a=%a:^=^^%"
call :suba %A%, %B%
goto :eof

:suba
echo.&echo.
echo The file %1 was created on %~t2 and contains %~z2 bytes.
echo Contents:
type %1
goto :eof

And this script only handles the special character "^".
There may be other characters that also require special
handling. (I wrote the above script after someone asked
in another Newsgroup how to do this.)

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On 21 Dec 2022, at 17:06, Chris Angelico <rosuav@gmail.com> wrote:

On Thu, 22 Dec 2022 at 03:58, gene heskett <gheskett@shentel.net> wrote:

On 12/21/22 11:22, Chris Angelico wrote:
On Thu, 22 Dec 2022 at 03:11, Stefan Ram <ram@zedat.fu-berlin.de> wrote: >>>>

Lars Liedtke <lal@solute.de> 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 you make a statement like that, Chris, you should also note that
every single one of those "wonky edge cases" is documented down to the
last dotted i. Bash's docs will kill a good sized pulp tree, needing
around a ream of paper to print on a duplex printer. I know, I did it
around a decade ago. If you like to write scripts, having a dead tree
copy of the docs at your elbow in incredibly useful. That huge man page
does not cover it like the printed docs do.

Oh yes, absolutely true. Its wonkiness is dependable and consistent;
but it is definitely quirky (look at all the different ways to embed arguments into things, and the ways that $*, $@, "$*, and "$@" behave
when put into variables). Not usually a problem, but it does sometimes
leave you thinking "wow, wouldn't it be easier to just use something
like Python?". And in the complicated cases, yeah, it can be. But in
the simple cases? Bash rocks.

I see bash scripts that are 1000’s of line of code at work and its a maintenance nightmare.

Knowing when to make the move from “handy bash script” to “this is a production application” and needs to be python is what I see people miss.

After a certain point in complexity the python code wins on maintenance. Personally i set a low bar to move from bash to python.

Barry

ChrisA
--
https://mail.python.org/mailman/listinfo/python-list

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ram@zedat.fu-berlin.de (Stefan Ram) writes:

echo 11111>aa.txt
timeout 62
echo 222222>a^^a.txt
timeout 62
echo 3333333>a^^^^a.txt

dir *.txt

setlocal enabledelayedexpansion
for /f %%i in ('dir /b *.txt') do (
SET "a=%%i"
SET "b=!a:^=^^!"
call :sub !b!
)
goto :eof

:sub
SET "A=%1"
SET "B=%1"
SET "a=%a:^=^^%"
call :suba %A%, %B%
goto :eof

:suba
echo.&echo.
echo The file %1 was created on %~t2 and contains %~z2 bytes.
echo Contents:
type %1
goto :eof

A similar Python script might be longer, but it deals with
getting the job done and not with fighting irregularities.
(Warning: This script may create/overwrite/delete files!)

import datetime
import pathlib
import time

for content, name in\
( ( '11111', 'aa.txt' ),( '222222', 'a^a.txt' ), ( '3333333', 'a^^a' )):
with open( name, "w" ) as stream:
print( content, file=stream )
time.sleep( 62 )

for file in pathlib.Path.cwd().glob( '*.txt' ):
print( 'The file '+ str( file )+' was created on '+
str( datetime.datetime.fromtimestamp( file.stat().st_ctime ))+
' and contains '+ str( file.stat().st_size )+' Bytes. ' )
print( 'Contents:' )
with open( file, 'r' )as stream: print( stream.read() )

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