How to trim whitespace from a Bash variable?

Question

I have a shell script with this code:

var=`hg st -R \"$path\"`
if [ -n \"$var\" ]; then
    echo $var
fi

But the conditional code always ex

Answer 1

Strip one leading and one trailing space

trim()
{
    local trimmed="$1"

    # Strip leading space.
    trimmed="${trimmed## }"
    # Strip trailing space.
    trimmed="${trimmed%% }"

    echo "$trimmed"
}

For example:

test1="$(trim " one leading")"
test2="$(trim "one trailing ")"
test3="$(trim " one leading and one trailing ")"
echo "'$test1', '$test2', '$test3'"

Output:

'one leading', 'one trailing', 'one leading and one trailing'

Strip all leading and trailing spaces

trim()
{
    local trimmed="$1"

    # Strip leading spaces.
    while [[ $trimmed == ' '* ]]; do
       trimmed="${trimmed## }"
    done
    # Strip trailing spaces.
    while [[ $trimmed == *' ' ]]; do
        trimmed="${trimmed%% }"
    done

    echo "$trimmed"
}

For example:

test4="$(trim "  two leading")"
test5="$(trim "two trailing  ")"
test6="$(trim "  two leading and two trailing  ")"
echo "'$test4', '$test5', '$test6'"

Output:

'two leading', 'two trailing', 'two leading and two trailing'