diff --git a/completions/_adb b/completions/_adb
index d1e3a8af5c6..f44c457fea1 100644
--- a/completions/_adb
+++ b/completions/_adb
@@ -5,9 +5,9 @@
 
 _comp_cmd_adb__command_usage()
 {
-    COMPREPLY=($(compgen -W \
-        '$("$1" help 2>&1 | command grep "^ *\(adb \)\? *$2 " \
-            | command sed -e "s/[]|[]/\n/g" | _parse_help -)' -- "$cur"))
+    COMPREPLY=($(compgen -W '$("$1" help 2>&1 | \
+            command sed -e "/^ *\(adb \)\{0,1\} *$2 /!d;s/[]|[]/\n/g" | \
+            _parse_help -)' -- "$cur"))
 }
 
 _comp_cmd_adb()
diff --git a/completions/_udevadm b/completions/_udevadm
index 0b207c1f1bf..7559404e29e 100644
--- a/completions/_udevadm
+++ b/completions/_udevadm
@@ -8,7 +8,7 @@ _comp_cmd_udevadm()
     local cur prev words cword was_split comp_args
     _comp_initialize -s -- "$@" || return
 
-    local i udevcmd has_udevcmd=""
+    local i udevcmd="" has_udevcmd=""
     for ((i = 1; i < cword; i++)); do
         if [[ ${words[i]} != -* ]]; then
             udevcmd=${words[i]}
@@ -69,7 +69,7 @@ _comp_cmd_udevadm()
 
     if [[ $cur == -* ]]; then
         COMPREPLY=($(compgen -W \
-            '$("$1" ${udevcmd-} --help 2>/dev/null | _parse_help -)' -- "$cur"))
+            '$(_parse_help "$1" "${udevcmd-} --help")' -- "$cur"))
         [[ ${COMPREPLY-} == *= ]] && compopt -o nospace
     fi
 } &&
diff --git a/completions/badblocks b/completions/badblocks
index 431723b1200..108b8915877 100644
--- a/completions/badblocks
+++ b/completions/badblocks
@@ -17,7 +17,7 @@ _comp_cmd_badblocks()
 
     if [[ $cur == -* ]]; then
         # Filter out -w (dangerous) and -X (internal use)
-        COMPREPLY=($(compgen -X -[wX] -W '$(_parse_usage "$1")' -- "$cur"))
+        COMPREPLY=($(compgen -X '-[wX]' -W '$(_parse_usage "$1")' -- "$cur"))
         return
     fi
 
diff --git a/completions/complete b/completions/complete
index 772aa0655c8..0e3f9d77162 100644
--- a/completions/complete
+++ b/completions/complete
@@ -40,7 +40,7 @@ _comp_cmd_complete()
         local -a opts=($(compgen -W '$(_parse_usage help "-s $1")' -- "$cur"))
         # -F, -C do not work the expected way with compgen
         [[ $1 != *compgen ]] || opts=("${opts[@]//-[FC]/}")
-        COMPREPLY=($(compgen -W '"${opts[@]}"' -- "$cur"))
+        COMPREPLY=($(compgen -W '"${opts[@]}"' -X '' -- "$cur"))
     else
         COMPREPLY=($(compgen -A command -- "$cur"))
     fi
diff --git a/completions/gnokii b/completions/gnokii
index c45f6b31e2f..785631c17c1 100644
--- a/completions/gnokii
+++ b/completions/gnokii
@@ -221,14 +221,18 @@ _comp_cmd_gnokii()
         esac
     fi
 
-    # safer to use LANG=C
-    local all_cmd="$(LANG=C _parse_help "$1" "--help all")"
-    # these 2 below are allowed in combination with others
-    local main_cmd=$(command grep -v -- '--config\|--phone' <<<"$all_cmd")
+    local all_cmd="$(_parse_help "$1" "--help all")"
 
+    # these 2 below are allowed in combination with others
+    local main_cmd
+    _comp_split -l main_cmd "$(command sed -e '/--config/d;/--phone/d' -e \
+        's/[][\(){}|^$*+?.]/\\&/g' <<<"$all_cmd")"
     # don't provide main command completions if one is
     # already on the command line
-    [[ $COMP_LINE =~ $(tr ' ' '\b|' <<<"$main_cmd") ]] && return
+    local IFS='|'
+    local regex_main_cmd="(${main_cmd[*]})($|[^_[:alnum:]])"
+    IFS=$' \t\n'
+    [[ $COMP_LINE =~ $regex_main_cmd ]] && return
 
     COMPREPLY=($(compgen -W "$all_cmd" -- "$cur"))
 } &&
diff --git a/completions/postfix b/completions/postfix
index 7b445ff54c5..d5899742145 100644
--- a/completions/postfix
+++ b/completions/postfix
@@ -17,11 +17,8 @@ _comp_cmd_postfix()
     esac
 
     if [[ $cur == -* ]]; then
-        COMPREPLY=($(
-            compgen -W \
-                '$(_bashcomp_try_faketty "$1" --help 2>&1 | _parse_usage -)' \
-                -- "$cur"
-        ))
+        COMPREPLY=($(compgen -W \
+            '$(_parse_usage _bashcomp_try_faketty "$1 --help")' -- "$cur"))
         return
     fi