Re: Cannot form valid test expressions that involve brackets as string comparison targets

[Greg Wooledge]

On Wed, Oct 07, 2009 at 08:07:19PM +1030, Lyall Pearce wrote:
> Description:
>     Cannot form expressions which involve left or right brackets.

Parentheses?

> Repeat-By:
> 
>         basePic="(2008-04)"
>     if [ "${basePic:0:1}" = '(' -a "${basePic:4:1}" = ')' ]
>     then
>         echo "Got brackets"
>     fi

  if [ "${basePic:0:1}" = "(" ] && [ "${basePic:(-1):1}" = ")" ]; then
    echo "Got parentheses"
  fi

When using [ instead of [[, I would strongly recommend never using -a
or -o inside it.  POSIX has strict rules about exactly how to treat
a [ command with a specific number of arguments, and often the most
common cases are technically illegal.  The workaround is to use multiple
[ commands strung together with && and || as needed.

Or, the other workaround would be to use [[, since you're already using
${string:start:length} which is non-POSIX syntax.

  if [[ "${basePic:0:1}" = "(" && "${basePic:(-1):1}" = ")" ]]; then
    echo "Got parentheses"
  fi

Both of those worked for me in bash 4.0.10.