[PATCH V3 2/4] bash-completion:fix shellcheck SC2207-Warning

[t . feng]

COMPREPLY=($(command)) are doing unquoted command expansion in an array.
This will invoke the shell's sloppy word splitting and glob expansion.

If we want to split the output into lines or words, use read -r and 
loops will be better. This prevents the shell from doing unwanted
splitting and glob expansion, and therefore avoiding problems with
output containing spaces or special characters.

SC2207 (warning): Prefer mapfile or read -a to split
command output (or quote to avoid splitting).

In grub-completion.bash.in line 56:
        COMPREPLY=($(compgen -P "${2-}" -W "${1-}" -S "${4-}" --
"$cur"))
                   ^-- SC2207 (warning)

In grub-completion.bash.in line 119:
        COMPREPLY=( $(compgen \
                    ^-- SC2207 (warning)

In grub-completion.bash.in line 128:
    COMPREPLY=( $( compgen -f -X '!*/*.mod' -- "${grub_dir}/$cur" | {
                ^-- SC2207 (warning)

More: https://github.com/koalaman/shellcheck/wiki/SC2207

Signed-off-by: "t.feng" <fengtao40@huawei.com>
---
 .../bash-completion.d/grub-completion.bash.in | 40 +++++++++++--------
 1 file changed, 24 insertions(+), 16 deletions(-)

diff --git a/util/bash-completion.d/grub-completion.bash.in 
b/util/bash-completion.d/grub-completion.bash.in
index 93d143480..d3399f0e1 100644
--- a/util/bash-completion.d/grub-completion.bash.in
+++ b/util/bash-completion.d/grub-completion.bash.in
@@ -52,8 +52,11 @@ __grubcomp () {
         COMPREPLY=()
         ;;
     *)
-        local IFS=' '$'\t'$'\n'
-        COMPREPLY=($(compgen -P "${2-}" -W "${1-}" -S "${4-}" -- "$cur"))
+        local line IFS=' '$'\t'$'\n'
+        COMPREPLY=()
+        while read -r line; do
+            COMPREPLY+=("${line}")
+        done < <(compgen -P "${2-}" -W "${1-}" -S "${4-}" -- "$cur")
         ;;
     esac
 }
@@ -115,25 +118,30 @@ __grub_list_menuentries () {
     local config_file=$(__grub_dir)/grub.cfg
 
     if [ -f "$config_file" ];then
-        local IFS=$'\n'
-        COMPREPLY=( $(compgen \
-            -W "$( awk -F "[\"']" '/menuentry/ { print $2 }' $config_file )" \
-            -- "$cur" )) #'# Help emacs syntax highlighting
+        local line IFS=$'\n'
+        COMPREPLY=()
+        while read -r line; do
+            COMPREPLY+=("${line}")
+        done < <(compgen \
+                -W "$( awk -F "[\"']" '/menuentry/ { print $2 }' $config_file 
)" \
+                -- "$cur" ) #'# Help emacs syntax highlighting
     fi
 }
 
 __grub_list_modules () {
     local grub_dir=$(__grub_dir)
-    local IFS=$'\n'
-    COMPREPLY=( $( compgen -f -X '!*/*.mod' -- "${grub_dir}/$cur" | {
-         while read -r tmp; do
-             [ -n "$tmp" ] && {
-                 tmp=${tmp##*/}
-                 printf '%s\n' ${tmp%.mod}
-             }
-         done
-         }
-        ))
+    local line tmp IFS=$'\n'
+    COMPREPLY=()
+    while read -r line; do
+        COMPREPLY+=("${line}")
+    done < <(compgen -f -X '!*/*.mod' -- "${grub_dir}/$cur" | {
+        while read -r tmp; do
+            [ -n "$tmp" ] && {
+                tmp=${tmp##*/}
+                printf '%s\n' ${tmp%.mod}
+            }
+        done
+    })
 }
 
 #
-- 
2.27.0