Fixed plenv-rehash for older GNU Bash

[simonmeggle]

plenv shims are only executable on older GNU bash versions (e.g. 3.1.17) when the regex is enclosed within quotes.

[syohex]

Does this change work for newer bash ?

Behaviour of Bash 3.2 or higher version is here

f.  Quoting the string argument to the [[ command's  =~ operator now forces
    string matching, as with the other pattern-matching operators.

See also

• http://tiswww.case.edu/php/chet/bash/NEWS

[ghost]

No, it does not; this commit would result in breakage.

For maximum cross-compatibility between the various bash versions, assign the regex to a variable first, then expand it as the RHS of the =~ operator without quoting it. For example:

re='^(--$|-[0A-Za-z]*[eE].*)'
for arg; do
  [[ "\$arg" =~ $re ]] && break

Alternatively, use extglobs (at the cost of being unfamiliar to those that don't spend much time hacking in bash):

shopt -s extglob
for arg; do
  [[ "\$arg" == @(--|-*([0A-Za-z])[eE]*) ]] && break

EDIT: Also, the code seems broken to begin with. Why is $arg quoted and the sigil escaped? Consider this bad code:

$ echo $BASH_VERSION
4.3.48(1)-release
$ ( set -x; foo=123; [[ "\$foo" == 123 ]] && echo "matched" )
+ foo=123
+ [[ $foo == 123 ]]

Then compare it to this:

$ ( set -x; foo=123; [[ $foo == 123 ]] && echo "matched" )
+ foo=123
+ [[ 123 == 123 ]]
+ echo matched
matched