Fixes regression introduced by 16406e63b3.
Not replacing "egrep" with a negated character class on [^e] needs to be
put back into the replacement, because if we have something like:
foo="$(grep xxx)"
The replacement would be something like this:
foo="$/nix/store/.../bin/grep xxx)"
Which will lead to wrong behavior and in cases of for example
"xdg-screensaver", even directly to a syntax error:
xdg-screensaver: line 178: syntax error near unexpected token `('
xdg-screensaver: line 178: `command="/nix/store/.../bin/grep -E
"^Exec(\[[^]=]*])?=" "$file" |
/nix/store/.../bin/cut -d= -f 2- |
first_word`"'
Signed-off-by: aszlig <aszlig@redmoonstudios.org>