convert sed to zsh

convert sed to zsh

[Ray Andrews]

I'm trying to convert a 'sed' filter to native zsh.  Here's the sed:

     bar=$( echo $foo |
     sed -r "s/\x1B\[([0-9]{1,2}(;[0-9]{1,2})?)?[mGK]//g" )

Here's my candidate zsh:

     bar=$foo//$'\x1B'\[([0-9](#c0,2)(;[0-9](#c0,2))#)#[mGK]/}

... so far it's working, but I'm nervous about it.  In another context 
it seems I have to backslash the semi-colon, but here it seems ok either 
way, but of course it should be one or the other. The 'sed' is of course 
the kosher way (I believe) of removing color codes and various other 
escapes like "\e[K" that seem to hang around colorized output of 'grep' 
and so on.  With several different forms of color codes, I want to be 
sure I get this right. Unless of course zsh already has a stock way of 
stripping escape sequences, which it very well might.

Re: convert sed to zsh

[Bart Schaefer]

On Nov 26,  9:49am, Ray Andrews wrote:
} Subject: convert sed to zsh
}
}      sed -r "s/\x1B\[([0-9]{1,2}(;[0-9]{1,2})?)?[mGK]//g"
} 
} Here's my candidate zsh:
} 
}      bar=$foo//$'\x1B'\[([0-9](#c0,2)(;[0-9](#c0,2))#)#[mGK]/}

That's a parse error, you're missing the opening curly brace.

You can write $'\x1B' as $'\e' for clarity.

Why change {1,2} in sed to (#c0,2) in zsh?  (#c1,2) should work.

} ... so far it's working, but I'm nervous about it.  In another context 
} it seems I have to backslash the semi-colon, but here it seems ok either 
} way, but of course it should be one or the other.

"Of course"?

The reason both ';' and '\;' work there has to do with the properties
of patterns rather than the properties of semicolons.  Semicolon is a
command terminator but otherwise is not special, so you need to protect
a literal semicolon only from command parsing [such as inside $(...)].

} The 'sed' is of course the kosher way (I believe) of removing color
} codes and various other escapes like "\e[K" that seem to hang around
} colorized output of 'grep' and so on.

I'm not quite an expert on color codes but the zsh expression should
do the same as the sed (modulo 1,2 vs. 0,2 as noted and assuming you
have extendedglob set).  I do know that there are other escapes (cursor
movements, overstriking, etc.) that won't match this expression, but
probably you never encounter those in the usage you expect.

Re: convert sed to zsh

[Ray Andrews]

On 11/26/2015 12:17 PM, Bart Schaefer wrote:
> On Nov 26,  9:49am, Ray Andrews wrote:
> } Subject: convert sed to zsh
> }
> }      sed -r "s/\x1B\[([0-9]{1,2}(;[0-9]{1,2})?)?[mGK]//g"
> }
> } Here's my candidate zsh:
> }
> }      bar=$foo//$'\x1B'\[([0-9](#c0,2)(;[0-9](#c0,2))#)#[mGK]/}
>
> That's a parse error, you're missing the opening curly brace.

Right. An edit-in-place error. Gotta be more careful about those they 
waste people's time.
>
> You can write $'\x1B' as $'\e' for clarity.
>
> Why change {1,2} in sed to (#c0,2) in zsh?  (#c1,2) should work.

I'm working from expressions taken verbatim and on faith, but that seem 
to either very slightly 'disagree' with each other, or to have different 
sets of codes they'll work with, or one is sightly sloppier than the 
other, so I'm being careful.  There could be syntax in one where no 
match is acceptable, but an error in the other or some such.  I know for 
most things zsh just uses different symbols vis a vis regex, but there's 
logic changes too so gotta be alert.
>
> } ... so far it's working, but I'm nervous about it.  In another context
> } it seems I have to backslash the semi-colon, but here it seems ok either
> } way, but of course it should be one or the other.
>
> "Of course"?

I don't want to guess.  If I backslash it will be because it's required.
>
> The reason both ';' and '\;' work there has to do with the properties
> of patterns rather than the properties of semicolons.  Semicolon is a
> command terminator but otherwise is not special, so you need to protect
> a literal semicolon only from command parsing [such as inside $(...)].

Ah, so the backslash is acceptable but not required in the way that you 
can backslash near anything.
>
> } The 'sed' is of course the kosher way (I believe) of removing color
> } codes and various other escapes like "\e[K" that seem to hang around
> } colorized output of 'grep' and so on.
>
> I'm not quite an expert on color codes but the zsh expression should
> do the same as the sed (modulo 1,2 vs. 0,2 as noted and assuming you
> have extendedglob set).  I do know that there are other escapes (cursor
> movements, overstriking, etc.) that won't match this expression, but
> probably you never encounter those in the usage you expect.

Yeah, just colors, for now, anyway.  I'm working from Sebastian's stuff, 
which started out being able to filter colors, but not the ' \e[K' thing 
that grep adds.  So I added a separate filter for that, but the 'sed' 
expression seems robust enough to handle that along with the color 
codes. So I'm reverse engineering that back to zsh syntax.  The sed 
expression has an obvious robustness about it--you can see that it will 
handle any color code that I know of, anyway.

Your edits in place and all good, thanks.
>