Remove leading and trailing white spaces

x <- '     middle of the string      '
sub("^[[:space:]]*(.*?)[[:space:]]*$", "\\1", x, perl=TRUE)

I have a character string and I would like to remove the leading and
tailing white spaces. ?The example for 'sub' shows how to remove the
trailing white spaces, but I still can't figure out how to remove both
trailing and leading white spaces because I can't find any documentation
for what "+$" means or what "\\s+$" means. ?Maybe its because I don't
have a Unix background. ?Thanks in advance for any help with this.

str <- ' ? ?Now is the time ? ? ?'
sub(' +$', '', str) ?## spaces only
sub('[[:space:]]+$', '', str) ## white space, POSIX-style
sub('\\s+$', '', str, perl = TRUE) ## Perl-style white space

Thanks,

Roger
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