Bash, weird variable scope when populating array with results

问题

I am parsing command output and putting results into array.

Works fine until exiting the inner loop - output array is empty.

declare -a KEYS

#-----------------------------------------------------------------------------#
get_keys()
{

# this extracts key NAMES from log in format "timestamp keycode"
$glue_dir/get_keys $ip | while read line; do
    echo line: $line
    set -- $line # $1 timestamp $2 keycode
    echo 1: $1 2: $2
    key=(`egrep "\\s$2$" "$glue_dir/keycodes"`) # tested for matching '40' against 401, 402 etc
    set -- $key # $1 key name $2 keycode
    KEYS+=("$1")
    echo key $1
    echo KEYS inside loop: "${KEYS[@]}"
done
    echo KEYS outside loop: "${KEYS[@]}"
}

The output when run agains two output lines:

line: 1270899320451 38
1: 1270899320451 2: 38
key UP
KEYS inside loop: UP
line: 1270899320956 40
1: 1270899320956 2: 40
key DOWN
KEYS inside loop: UP DOWN
KEYS outside loop:

I spent an hour trying to figure this out. Please help. ;-)

回答1:

When you use a pipe (|) to pass your command output to while, your while loop runs in a subshell. When the loop ends, your subshell terminates and your variables will not be available outside your loop.

Use process substitution instead:

while read line; do
   # ...
done < <($glue_dir/get_keys $ip)

来源：https://stackoverflow.com/questions/7612320/bash-weird-variable-scope-when-populating-array-with-results