On Wed, 28 Jun 2023 12:42:16 +0200
Fabien Orjollet <of1+bugb...@disroot.org> wrote:
> On 28/06/2023 00:40, Kerin Millar wrote:
> > On Tue, 27 Jun 2023 21:52:53 +0200
> > of1 <o...@disroot.org> wrote:
> >
> >> On 27/06/2023 21:05, Kerin Millar wrote:
> >>> It doesn't work at all for >=5.2. The reason for this is interesting and
> >>> I may make a separate post about it.
> >>>
> >>> Prior to 5.2, it can easily be tricked into printing names that do not
> >>> exist.
> >>>
> >>> $ VAR=$'\nNONEXISTENT=' ./declare-P | grep ^NONEXISTENT
> >>> NONEXISTENT
> >>>
> >> Thank you. I was just reading the discussion in Gentoo forum and
> >> realizing that I've been to quickly: it doesn't pass the
> >> FOO=$'\nBAR BAZ QUUX=' test. But what about this? (I also quickly
> >> tested with Bash 5.2.15).
> >>
> >>
> >> FOO=$'\nBAR BAZ QUUX='
> >> VAR=$'\nNONEXISTENT='
> >>
> >> declare-P() {
> >> local curVar
> >> declare -a curVars
> >>
> >> readarray -t curVars <<<"$1"
> >> curVars=( "${curVars[@]%%=*}" )
> >> curVars=( "${curVars[@]##* }" )
> >> for curVar in "${curVars[@]}"; do
> >> ### we can use [[ -v "$curVar" ]] at some point!
> >> [[ "${curVar//[a-zA-Z0-9_]}" || \
> >> "${curVar:0:1}" == [0-9] || \
> >> ! -v "$curVar" || \
> >> ! "$curVar" =~ $2 ]] || printf '%s\n' "$curVar"
> >> done
> >> }
> >>
> >> declare-P "$(declare -p)"
> >> echo "##################"
> >> declare-P "$(declare -p)" "QU|^NON|VAR"r
> >>
> >
> > This use of test -v is probably sufficient to address that particular
> > issue. It is just as well that the test occurs after determining that the
> > string is a valid identifier because test -v has the power to facilitate
> > arbitrary code execution.
> >
> > My assertion that your code is broken in 5.2 was incorrect. Rather, the
> > problem seems to be that regcomp(3) behaviour differs across platforms,
> > where given an empty expression to compile. To address that, you could
> > determine whether a second positional parameter was given and is non-empty
> > before proceeding to use it.
>
> Thank you, good to know. I think that ${2:-.} should be correct.
>
> >
> > Curiously, repeated invocation may lead to obvious issues of resource
> > consumption.
> >
> > # This is excruciatingly expensive
> > time for i in {1..100}; do
> > declare-P "$(declare -p)"
> > done
> >
> > # This is not so expensive (!)
> > time for i in {1..100}; do
> > declare-P "$(declare -p)"
> > :
> > done
>
> I made some testing by adding
> echo -n "$(( ++COUNT ))>$(wc -c <<<"$1") "
> echo "$1" >"/tmp/declare-P$COUNT"
> to the function:
>
> 1>4651 2>9785 3>15283 4>21504 5>29173 6>39739 7>56095 8>84036
> 9>135145 10>232592 11>422710 12>798174 13>1544326 14>3031854
> 15>6002134 16>11937918 ^C
>
> ls -rtnh /tmp/declare-P*
> -rw-r--r-- 1 1000 1000 4,6K 28 juin 11:09 /tmp/declare-P1
> -rw-r--r-- 1 1000 1000 9,6K 28 juin 11:09 /tmp/declare-P2
> -rw-r--r-- 1 1000 1000 15K 28 juin 11:09 /tmp/declare-P3
> -rw-r--r-- 1 1000 1000 21K 28 juin 11:09 /tmp/declare-P4
> -rw-r--r-- 1 1000 1000 29K 28 juin 11:09 /tmp/declare-P5
> -rw-r--r-- 1 1000 1000 39K 28 juin 11:09 /tmp/declare-P6
> -rw-r--r-- 1 1000 1000 55K 28 juin 11:09 /tmp/declare-P7
> -rw-r--r-- 1 1000 1000 83K 28 juin 11:09 /tmp/declare-P8
> -rw-r--r-- 1 1000 1000 132K 28 juin 11:09 /tmp/declare-P9
> -rw-r--r-- 1 1000 1000 228K 28 juin 11:09 /tmp/declare-P10
> -rw-r--r-- 1 1000 1000 413K 28 juin 11:09 /tmp/declare-P11
> -rw-r--r-- 1 1000 1000 780K 28 juin 11:09 /tmp/declare-P12
> -rw-r--r-- 1 1000 1000 1,5M 28 juin 11:09 /tmp/declare-P13
> -rw-r--r-- 1 1000 1000 2,9M 28 juin 11:09 /tmp/declare-P14
> -rw-r--r-- 1 1000 1000 5,8M 28 juin 11:09 /tmp/declare-P15
> -rw-r--r-- 1 1000 1000 12M 28 juin 11:09 /tmp/declare-P16
>
> But by adding set -p to the subshell:
Your best option would probably be to run declare -p within the function while
avoiding the use of command substitution altogether, so as not to 'pollute' the
_ variable.
--
Kerin Millar
