Re: colored verbose

[alex xmb sw ratchev]

On Wed, Nov 8, 2023, 3:02 PM lacsaP Patatetom <patatetom@gmail.com> wrote:

> bash's verbose mode makes it possible to "exploit" comments and "preserve"
> code (pipe characters don't disappear for example)
>

i dont get it ..

Le mer. 8 nov. 2023 à 13:48, Greg Wooledge <greg@wooledge.org> a écrit :
>
> > On Wed, Nov 08, 2023 at 11:26:36AM +0100, lacsaP Patatetom wrote:
> > > is it possible to distinguish the lines displayed by bash's verbose
> mode
> > by
> > > coloring them ?
> >
> > First of all, bash's "verbose mode" is usually worthless.  It is NOT
> > the same as trace mode (-x).  Usually you want trace mode instead.
> > However, I'll give you the benefit of the doubt and assume you either
> > have some compelling need for verbose mode, or that you're clever enough
> > to replace -v with -x once you realize that's what you really want.
> >
> > Now, on to the answer:
> >
> > Not as such.  However, we can determine experimentally that "verbose
> mode"
> > writes lines to stderr:
> >
> > unicorn:~$ bash -v foo >/dev/null
> > #!/bin/bash
> > echo hello world
> > true
> >
> > (It's actually undocumented.  Probably because nobody uses verbose mode
> > or cares about it.  Seriously, trace mode is what you want.  It even
> > lets you specify a custom FD, so you can intercept *only* trace mode
> > output, and not ordinary stderr, if that's useful to you.)
> >
> > Knowing this, we could set up a filter that intercepts stderr, and adds
> > colorization around each "line" written there.  Doing this will cause
> > desynchronization of the stdout and stderr streams, so only do it if
> > this is not a problem for your script.
> >
> > Also, if you don't arrange for the stderr filter to be terminated and
> > waited for, you may get the next shell prompt before you get the filtered
> > stderr lines.
> >
> > > for example, with this little script, make the first and third
> displayed
> > > lines stand out by coloring them :
> > >
> > > bash -v <<~~~
> > > echo hello world
> > > seq 5
> > > ~~~
> > > echo hello world
> > > hello world
> > > seq 5
> > > 1
> > > 2
> > > 3
> > > 4
> > > 5
> >
> > Yeah, see, you are NOT going to get the individual lines of the streams
> > in the correct order if you do this.  Maybe that's a problem for you, and
> > maybe it's not.  I dunno.
> >
> > Anyway, here's a simplistic implementation to play with:
> >
> > ========================================================================
> > #!/bin/bash
> > # Set up stderr filtering, and then turn on verbose mode.
> > filter() {
> >     local red=$(tput setaf 1)
> >     local sgr0=$(tput sgr0)
> >     local line IFS=''
> >     while read -r line; do
> >         printf '%s%s%s\n' "$red" "$line" "$sgr0"
> >     done
> > }
> >
> > exec 2> >(filter >&2)
> > trap 'exec 2>&-; wait' EXIT
> > set -v
> >
> > # Actual script:
> > echo hello world
> > true
> > ========================================================================
> >
> > And running it:
> >
> > ========================================================================
> > unicorn:~$ ./foo
> > hello world
> >
> > # Actual script:
> > echo hello world
> > true
> > exec 2>&-; wait
> > unicorn:~$
> > ========================================================================
> >
> > Everything from "#" to "wait" is red.  Stderr was delayed by the
> > filtering, as expected.
> >
> > With a slightly different script it becomes a little less terrible:
> >
> > ========================================================================
> > unicorn:~$ ./foo
> >
> > (RED) # Actual script:
> > (RED) sleep 1
> > hello world
> > (RED) echo hello world
> > (RED) sleep 1
> > good-bye
> > (RED) echo good-bye
> > (RED) exec 2>&-; wait
> > unicorn:~$
> > ========================================================================
> >
> > I added (RED) in front of each colorized line in this example.  When
> > the commands take longer to run, the desynchronization becomes less
> > of an issue.  Slightly.  Here's an even better demonstration:
> >
> > ========================================================================
> > unicorn:~$ ./foo
> >
> > (RED) # Actual script:
> > (RED) sleep 1; echo hello world
> > hello world
> > (RED) sleep 1; echo good-bye
> > good-bye
> > (RED) exec 2>&-; wait
> > unicorn:~$
> > ========================================================================
> >
> > If *every* line full of commands has a significant delay before it
> > writes output, then you won't even notice the desynchronization.  Anyway,
> > that's what we've got.  Have fun.
> >
> >
>