Stripping spaces from a shell variable, portably

[DervishD <raul@xxxxxxxxxxxx>]

    Hi all :))

    I need to strip leading and trailing spaces from the contents of
a shell variable, and I need to do it portably, with a construct like
${...%% } and with no loops. When I say 'portably' I mean using SuSv3
constructs, not Zsh extensions.

    I've tried the obvious ${variable# } for stripping a single
space, but this needs a while loop, which I want to avoid (although
it seems to be portable):

    while [ "$variable" != "${variable# }" ]
    do
        variable="${variable# }"
    done

    And the same with the '%' construct. Please note that I cannot
use '[[' for the test, since it must be portable, and this involves
exec'ing the 'test' binary for each space in the variable :((

    If no solution is possible I'll use 'tr', because the shell code
must run in bash and zsh at least, but I really want it to be able to
run in any SuSv3 compliant shell.

    Thanks a lot for your help :)

    Raúl Núñez de Arenas Coronado

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