adopt shellcheck recommendations (as in bug #2902)

ssh-copy-id

@@ -34,13 +34,15 @@
 # Shell script to install your public key(s) on a remote machine
 # See the ssh-copy-id(1) man page for details
 
+# shellcheck shell=dash
+
 # check that we have something mildly sane as our shell, or try to find something better
 if false ^ printf "%s: WARNING: ancient shell, hunting for a more modern one... " "$0"
 then
   SANE_SH=${SANE_SH:-/usr/bin/ksh}
   if printf 'true ^ false\n' | "$SANE_SH"
   then
-    printf "'%s' seems viable.\n" "$SANE_SH"
+    printf "'%s' seems viable.\\n" "$SANE_SH"
     exec "$SANE_SH" "$0" "$@"
   else
     cat <<-EOF
@@ -52,12 +54,13 @@ then
 	  a bug describing your setup, and the shell you used to make it work.
 
 	EOF
-    printf "%s: ERROR: Less dimwitted shell required.\n" "$0"
+    printf '%s: ERROR: Less dimwitted shell required.\n' "$0"
     exit 1
   fi
 fi
 
-DEFAULT_PUB_ID_FILE=$(ls -t ${HOME}/.ssh/id*.pub 2>/dev/null | grep -v -- '-cert.pub$' | head -n 1)
+# shellcheck disable=SC2010
+DEFAULT_PUB_ID_FILE=$(ls -t "${HOME}"/.ssh/id*.pub 2>/dev/null | grep -v -- '-cert.pub$' | head -n 1)
 
 usage () {
   printf 'Usage: %s [-h|-?|-f|-n] [-i [identity_file]] [-p port] [-F alternative ssh_config file] [[-o <ssh -o options>] ...] [user@]hostname\n' "$0" >&2
@@ -69,18 +72,18 @@ usage () {
 
 # escape any single quotes in an argument
 quote() {
-  printf "%s\n" "$1" | sed -e "s/'/'\\\\''/g"
+  printf '%s\n' "$1" | sed -e "s/'/'\\\\''/g"
 }
 
 use_id_file() {
   local L_ID_FILE="$1"
 
   if [ -z "$L_ID_FILE" ] ; then
-    printf "%s: ERROR: no ID file found\n" "$0"
+    printf '%s: ERROR: no ID file found\n' "$0"
     exit 1
   fi
 
-  if expr "$L_ID_FILE" : ".*\.pub$" >/dev/null ; then
+  if expr "$L_ID_FILE" : '.*\.pub$' >/dev/null ; then
     PUB_ID_FILE="$L_ID_FILE"
   else
     PUB_ID_FILE="$L_ID_FILE.pub"
@@ -93,7 +96,7 @@ use_id_file() {
     ErrMSG=$( { : < "$f" ; } 2>&1 ) || {
       local L_PRIVMSG=""
       [ "$f" = "$PRIV_ID_FILE" ] && L_PRIVMSG="	(to install the contents of '$PUB_ID_FILE' anyway, look at the -f option)"
-      printf "\n%s: ERROR: failed to open ID file '%s': %s\n" "$0" "$f" "$(printf "%s\n%s\n" "$ErrMSG" "$L_PRIVMSG" | sed -e 's/.*: *//')"
+      printf "\\n%s: ERROR: failed to open ID file '%s': %s\\n" "$0" "$f" "$(printf '%s\n%s\n' "$ErrMSG" "$L_PRIVMSG" | sed -e 's/.*: *//')"
       exit 1
     }
   done
@@ -110,10 +113,10 @@ do
 
   case "$OPT" in
     i)
-  	[ "${SEEN_OPT_I}" ] && {
-        	printf "\n%s: ERROR: -i option must not be specified more than once\n\n" "$0"
-        	usage
-  	}
+      [ "${SEEN_OPT_I}" ] && {
+        printf '\n%s: ERROR: -i option must not be specified more than once\n\n' "$0"
+        usage
+      }
       SEEN_OPT_I="yes"
       use_id_file "${OPTARG:-$DEFAULT_PUB_ID_FILE}"
       ;;
@@ -146,16 +149,18 @@ if [ $# != 1 ] ; then
 fi
 
 # drop trailing colon
-USER_HOST="$@"
+USER_HOST="$*"
 # tack the hostname onto SSH_OPTS
 SSH_OPTS="${SSH_OPTS:+$SSH_OPTS }'$(quote "$USER_HOST")'"
 # and populate "$@" for later use (only way to get proper quoting of options)
 eval set -- "$SSH_OPTS"
 
+# shellcheck disable=SC2086
 if [ -z "$(eval $GET_ID)" ] && [ -r "${PUB_ID_FILE:=$DEFAULT_PUB_ID_FILE}" ] ; then
   use_id_file "$PUB_ID_FILE"
 fi
 
+# shellcheck disable=SC2086
 if [ -z "$(eval $GET_ID)" ] ; then
   printf '%s: ERROR: No identities found\n' "$0" >&2
   exit 1
@@ -166,6 +171,7 @@ fi
 populate_new_ids() {
   local L_SUCCESS="$1"
 
+  # shellcheck disable=SC2086
   if [ "$FORCED" ] ; then
     NEW_IDS=$(eval $GET_ID)
     return
@@ -175,17 +181,20 @@ populate_new_ids() {
   eval set -- "$SSH_OPTS"
 
   umask 0177
-  local L_TMP_ID_FILE=$(mktemp ~/.ssh/ssh-copy-id_id.XXXXXXXXXX)
+  local L_TMP_ID_FILE
+  L_TMP_ID_FILE=$(mktemp ~/.ssh/ssh-copy-id_id.XXXXXXXXXX)
   if test $? -ne 0 || test "x$L_TMP_ID_FILE" = "x" ; then
     printf '%s: ERROR: mktemp failed\n' "$0" >&2
     exit 1
   fi
   local L_CLEANUP="rm -f \"$L_TMP_ID_FILE\" \"${L_TMP_ID_FILE}.stderr\""
+  # shellcheck disable=SC2064
   trap "$L_CLEANUP" EXIT TERM INT QUIT
   printf '%s: INFO: attempting to log in with the new key(s), to filter out any that are already installed\n' "$0" >&2
+  # shellcheck disable=SC2086
   NEW_IDS=$(
     eval $GET_ID | {
-      while read ID || [ "$ID" ] ; do
+      while read -r ID || [ "$ID" ] ; do
         printf '%s\n' "$ID" > "$L_TMP_ID_FILE"
 
         # the next line assumes $PRIV_ID_FILE only set if using a single id file - this
@@ -218,7 +227,7 @@ populate_new_ids() {
   fi
   if [ -z "$NEW_IDS" ] ; then
     printf '\n%s: WARNING: All keys were skipped because they already exist on the remote system.\n' "$0" >&2
-    printf '\t\t(if you think this is a mistake, you may want to use -f option)\n\n' "$0" >&2
+    printf '\t\t(if you think this is a mistake, you may want to use -f option)\n\n' >&2
     exit 0
   fi
   printf '%s: INFO: %d key(s) remain to be installed -- if you are prompted now it is to install the new keys\n' "$0" "$(printf '%s\n' "$NEW_IDS" | wc -l)" >&2
@@ -241,7 +250,7 @@ installkeys_sh() {
   INSTALLKEYS_SH=$(tr '\t\n' ' ' <<-EOF)
 	cd;
 	umask 077;
-	mkdir -p $(dirname ${AUTH_KEY_FILE}) &&
+	mkdir -p $(dirname "${AUTH_KEY_FILE}") &&
 	  { [ -z \`tail -1c ${AUTH_KEY_FILE} 2>/dev/null\` ] || echo >> ${AUTH_KEY_FILE}; } &&
 	  cat >> ${AUTH_KEY_FILE} ||
 	  exit 1;
@@ -257,12 +266,13 @@ EOF
 REMOTE_VERSION=$(ssh -v -o PreferredAuthentications=',' -o ControlPath=none "$@" 2>&1 |
                  sed -ne 's/.*remote software version //p')
 
+# shellcheck disable=SC2029
 case "$REMOTE_VERSION" in
   NetScreen*)
     populate_new_ids 1
     for KEY in $(printf "%s" "$NEW_IDS" | cut -d' ' -f2) ; do
-      KEY_NO=$(($KEY_NO + 1))
-      printf "%s\n" "$KEY" | grep ssh-dss >/dev/null || {
+      KEY_NO=$((KEY_NO + 1))
+      printf '%s\n' "$KEY" | grep ssh-dss >/dev/null || {
          printf '%s: WARNING: Non-dsa key (#%d) skipped (NetScreen only supports DSA keys)\n' "$0" "$KEY_NO" >&2
          continue
       }
@@ -270,7 +280,7 @@ case "$REMOTE_VERSION" in
       if [ $? = 255 ] ; then
         printf '%s: ERROR: installation of key #%d failed (please report a bug describing what caused this, so that we can make this message useful)\n' "$0" "$KEY_NO" >&2
       else
-        ADDED=$(($ADDED + 1))
+        ADDED=$((ADDED + 1))
       fi
     done
     if [ -z "$ADDED" ] ; then