Re: help with pattern matching needed

[Chet Ramey]

On 1/7/22 2:20 AM, Lawrence Velázquez wrote:



> > Case 2:
> > *******
> > A string like:
> > [.*^$[\]
> > should end up (after quote removal) as the pattern:
> > [.*^$[]
> > an AFAIU be valid (but of course not match the literal \), but bash
> > complains about a missing matching ].
> > That construct executes e.g. in (d)ash, though it never matches (or at
> > least not with the plain single characters).
>
> It looks like \] is being treated as a literal ] in both cases.
> The difference seems to be in the parsing: dash gives up on the
> bracket expression, while bash consumes the rest of the script
> trying to close it.
>
>      % cat ex1.sh
>      case $1 in
>          [.*^$[\]) printf '%s matched\n' "$1" ;;
>          *) printf "%s didn't match\\n" "$1" ;;
>      esac

The parser sees the (deprecated) `$[' and tries to read an entire `$[]'
expansion as part of a word. It fails to close that expansion and reports
an EOF error.


> That is it, though.  The empty $[] substitutes "0" into the pattern.
>
>      % cat ex2.sh
>      case $1 in
>          [.*^$[]) printf '%s matched\n' "$1" ;;
>          *) printf "%s didn't match\\n" "$1" ;;
>      esac
>      % bash ex2.sh '[.xxxxxxx^0'
>      [.xxxxxxx^0 matched
>
> However, as you noted, bash doesn't parse quite so greedily this
> time.  I don't know why not.

Because the closing `]' isn't escaped and the $[] expansion is complete.


--
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    chet@case.edu    http://tiswww.cwru.edu/~chet/