implement tab-completion of field names

This uses the new format string infrastructure to display
just fieldnames in a subshell so that the fields in a specific
account can be tab-completed.  In order for lpass to know which
account is being queried, you have to specify account name first,
like:

    lpass show foo --field [tab]

There's a slight annoyance that title cannot go away completely,
so post-process with egrep to drop those.

Signed-off-by: Bob Copeland <[email protected]>

contrib/lpass_bash_completion

@@ -1,3 +1,19 @@
+__lpass_complete_fieldname()
+{
+    local acct=$1
+    local cur=$2
+    local matches
+
+    matches=$(lpass show $acct --format='%fn' --title-format=' ' | \
+              egrep -v '^ $')
+
+    local IFS=$'\n'
+    COMPREPLY=($(compgen -W "$matches" "$cur"))
+    if [[ ! -z $COMPREPLY ]]; then
+        COMPREPLY=($(printf "%q\n" "${COMPREPLY[@]}"))
+    fi
+}
+
 __lpass_complete_name()
 {
     local cur=$1
@@ -33,6 +49,7 @@ __lpass_complete_opt()
 {
     local cmd=$1
     local cur=$2
+    local name=$3
     opts=""
 
     case "$cmd" in
@@ -69,6 +86,7 @@ _lpass()
     local cur="${COMP_WORDS[COMP_CWORD]}"
     local cmd="${COMP_WORDS[1]}"
     local subcmd="${COMP_WORDS[2]}"
+    local prev="${COMP_WORDS[COMP_CWORD-1]}"
     local optind=1
 
     for i in `seq 2 $COMP_CWORD`; do
@@ -78,6 +96,8 @@ _lpass()
         fi
     done
 
+    local name="${COMP_WORDS[$optind]}"
+
     local all_cmds="
         login logout passwd show ls mv add edit generate
         duplicate rm sync export import share
@@ -103,6 +123,13 @@ _lpass()
 
     COMPREPLY=()
 
+    case "$prev" in
+        --field)
+            __lpass_complete_fieldname $name $cur
+            return
+            ;;
+    esac
+
     case "$cur" in
         -*)
             __lpass_complete_opt $cmd $cur