diff --git a/Makefile b/Makefile
index dc98502..9b07e09 100644
--- a/Makefile
+++ b/Makefile
@@ -199,6 +199,9 @@ dist: distclean documentation
 /tmp/ccollect:
 	mkdir -p /tmp/ccollect
 
+shellcheck: ./ccollect
+	shellcheck -s sh -f gcc -x ./ccollect
+
 test: $(CCOLLECT_SOURCE) /tmp/ccollect
 	cd ./conf/sources/; for s in *; do CCOLLECT_CONF=../ ../../ccollect daily "$$s"; done
 	touch /tmp/ccollect/$$(ls /tmp/ccollect | head -n1).ccollect-marker
diff --git a/ccollect b/ccollect
index 4fa6da3..6dd3fc0 100755
--- a/ccollect
+++ b/ccollect
@@ -27,9 +27,9 @@ set -u
 #
 # Standard variables (stolen from cconf)
 #
-__pwd="$(pwd -P)"
-__mydir="${0%/*}"; __abs_mydir="$(cd "$__mydir" && pwd -P)"
-__myname=${0##*/}; __abs_myname="$__abs_mydir/$__myname"
+__mydir="${0%/*}"
+__abs_mydir="$(cd "$__mydir" && pwd -P)"
+__myname=${0##*/}
 
 #
 # where to find our configuration and temporary file
@@ -41,7 +41,8 @@ CPREEXEC="${CDEFAULTS}/pre_exec"
 CPOSTEXEC="${CDEFAULTS}/post_exec"
 CMARKER=".ccollect-marker"
 
-export TMP="$(mktemp "/tmp/${__myname}.XXXXXX")"
+TMP="$(mktemp "/tmp/${__myname}.XXXXXX")"
+export TMP
 CONTROL_PIPE="/tmp/${__myname}-control-pipe"
 
 VERSION="2.6"
@@ -76,6 +77,7 @@ LOCKFD=4
 lock_flock()
 {
     # $1 = source to backup
+    # shellcheck disable=SC2059
     lockfile="${LOCKDIR}/$(printf "${LOCKFILE_PATTERN}" "$1")"
     eval "exec ${LOCKFD}> ${lockfile}"
 
@@ -85,6 +87,7 @@ lock_flock()
 unlock_flock()
 {
     # $1 = source to backup
+    # shellcheck disable=SC2059
     lockfile="${LOCKDIR}/$(printf "${LOCKFILE_PATTERN}" "$1")"
     eval "exec ${LOCKFD}>&-"
     rm -f "${lockfile}"
@@ -96,6 +99,7 @@ unlock_flock()
 lock_mkdir()
 {
     # $1 = source to backup
+    # shellcheck disable=SC2059
     lockfile="${LOCKDIR}/$(printf "${LOCKFILE_PATTERN}" "$1")"
 
     mkdir "${lockfile}" && return 0 || return 1
@@ -104,6 +108,7 @@ lock_mkdir()
 unlock_mkdir()
 {
     # $1 = source to backup
+    # shellcheck disable=SC2059
     lockfile="${LOCKDIR}/$(printf "${LOCKFILE_PATTERN}" "$1")"
 
     rmdir "${lockfile}"
@@ -112,7 +117,7 @@ unlock_mkdir()
 #
 # determine locking tool: flock or mkdir
 #
-if $(which flock > /dev/null 2>&1)
+if command -v flock > /dev/null 2>&1
 then
     lockf="lock_flock"
     unlockf="unlock_flock"
@@ -137,6 +142,7 @@ LOGONLYERRORS=""
 # catch signals
 #
 TRAPFUNC="rm -f \"${TMP}\""
+# shellcheck disable=SC2064
 trap "${TRAPFUNC}" 1 2 15
 
 #
@@ -147,7 +153,7 @@ trap "${TRAPFUNC}" 1 2 15
 # see: http://www.tldp.org/LDP/abs/html/intandnonint.html
 _is_interactive()
 {
-    [ -t 0 -o -p /dev/stdin ]
+    [ -t 0 ] || [ -p /dev/stdin ]
 }
 
 #
@@ -163,26 +169,26 @@ delete_from_file()
     # dirs for deletion will be moved to this trash dir inside destination dir
     # - for fast mv operation
     trash="$(mktemp -d ".trash.XXXXXX")"
-    while read to_remove; do
+    while read -r to_remove; do
         mv "${to_remove}" "${trash}" ||
             _exit_err "Moving ${to_remove} to ${trash} failed."
         set -- "$@" "${to_remove}"
         if [ "${suffix}" ]; then
-            to_remove_no_suffix="$(echo ${to_remove} | sed "s/$suffix\$//")"
+            to_remove_no_suffix="$(echo "${to_remove}" | sed "s/$suffix\$//")"
             mv "${to_remove_no_suffix}" "${trash}" ||
                 _exit_err "Moving ${to_remove_no_suffix} to ${trash} failed."
             set -- "$@" "${to_remove_no_suffix}"
         fi
     done < "${file}"
-    _techo "Removing $@ in ${trash}..."
+    _techo "Removing $* in ${trash}..."
     empty_dir=".empty-dir"
     mkdir "${empty_dir}" || _exit_err "Empty directory ${empty_dir} cannot be created."
     [ "${VVERBOSE}" ] && echo "Starting: rsync -a --delete ${empty_dir} ${trash}"
     # rsync needs ending slash for directory content
-    rsync -a --delete "${empty_dir}/" "${trash}/" || _exit_err "Removing $@ failed."
+    rsync -a --delete "${empty_dir}/" "${trash}/" || _exit_err "Removing $* failed."
     rmdir "${trash}" || _exit_err "Removing ${trash} directory failed"
     rmdir "${empty_dir}" || _exit_err "Removing ${empty_dir} directory failed"
-    _techo "Removing $@ in ${trash} finished."
+    _techo "Removing $* in ${trash} finished."
 }
 
 display_version()
@@ -232,7 +238,7 @@ unlock()
 # stdout version
 _techo_stdout()
 {
-    echo "$(${DDATE}): $@"
+    echo "$(${DDATE}): $*"
 }
 
 # syslog version
@@ -260,14 +266,16 @@ _techo()
 {
     if [ "${LOGLEVEL}" = "a" ]
     then
-        set -- ${name:+"[${name}]"} $@
+        # name is exported before calling this function
+        # shellcheck disable=SC2154
+        set -- ${name:+"[${name}]"} "$@"
         "${_techof}" "$@"
     fi
 }
 
 _techo_err()
 {
-    _techo "Error: $@"
+    _techo "Error: $*"
 }
 
 _exit_err()
@@ -368,7 +376,7 @@ else
     LOGLEVEL="a"
 fi
 
-if [ "${LOGFILE}" -o "${SYSLOG}" ]
+if [ "${LOGFILE}" ] || [ "${SYSLOG}" ]
 then
     if [ "${LOGONLYERRORS}" ]
     then
@@ -378,8 +386,7 @@ fi
 
 # check that MAX_JOBS is natural number > 0
 # empty string means run all in parallel
-echo "${MAX_JOBS}" | grep -q -E '^[1-9][0-9]*$|^$'
-if [ "$?" -ne 0 ]
+if ! echo "${MAX_JOBS}" | grep -q -E '^[1-9][0-9]*$|^$'
 then
     _exit_err "Invalid max jobs value \"${MAX_JOBS}\""
 fi
@@ -412,19 +419,22 @@ if [ "${USE_ALL}" = 1 ]; then
     ( cd "${CSOURCES}" && ls -1 > "${TMP}" ) || \
         _exit_err "Listing of sources failed. Aborting."
 
-    while read tmp; do
-        eval export source_${no_sources}=\"${tmp}\"
-        no_sources=$((${no_sources}+1))
+    while read -r tmp; do
+        eval export "source_${no_sources}=\"${tmp}\""
+        no_sources=$((no_sources + 1))
     done < "${TMP}"
 else
     #
     # Get sources from command line
     #
     while [ "$#" -ge 1 ]; do
-        eval arg=\"\$1\"; shift
+        eval "arg=\"\$1\""
+        shift
 
-        eval export source_${no_sources}=\"${arg}\"
-        no_sources="$((${no_sources}+1))"
+        # arg is assigned in the eval above
+        # shellcheck disable=SC2154
+        eval export "source_${no_sources}=\"${arg}\""
+        no_sources="$((no_sources + 1))"
     done
 fi
 
@@ -461,6 +471,7 @@ if [ "${PARALLEL}" ]; then
     # fd 5 is tied to control pipe
     eval "exec 5<>${CONTROL_PIPE}"
     TRAPFUNC="${TRAPFUNC}; rm -f \"${CONTROL_PIPE}\""
+    # shellcheck disable=SC2064
     trap "${TRAPFUNC}" 0 1 2 15
 
     # determine how much parallel jobs to prestart
@@ -483,7 +494,7 @@ while [ "${source_no}" -lt "${no_sources}" ]; do
     # Get current source
     #
     eval export name=\"\$source_${source_no}\"
-    source_no=$((${source_no}+1))
+    source_no=$((source_no + 1))
 
     #
     # Start ourself, if we want parallel execution
@@ -498,12 +509,12 @@ while [ "${source_no}" -lt "${no_sources}" ]; do
         then
             # run prestart child if pending
             { "$0" "${INTERVAL}" "${name}"; printf '\n' >&5; } &
-            prestart=$((${prestart} - 1))
+            prestart=$((prestart - 1))
             continue
         else
             # each time a child finishes we get a line from the pipe
             # and then launch another child
-            while read line
+            while read -r line
             do
                 { "$0" "${INTERVAL}" "${name}"; printf '\n' >&5; } &
                 # get out of loop so we can contnue with main loop
@@ -557,6 +568,7 @@ while [ "${source_no}" -lt "${no_sources}" ]; do
 
     # redefine trap to also unlock (rm lockfile)
     TRAPFUNC="${TRAPFUNC}; unlock \"${name}\""
+    # shellcheck disable=SC2064
     trap "${TRAPFUNC}" 1 2 15
 
     #
@@ -576,10 +588,10 @@ while [ "${source_no}" -lt "${no_sources}" ]; do
     for opt in verbose very_verbose summary exclude rsync_options \
                   delete_incomplete rsync_failure_codes  \
                   mtime quiet_if_down ; do
-        if [ -f "${backup}/${opt}" -o -f "${backup}/no_${opt}"  ]; then
-            eval c_$opt=\"${backup}/$opt\"
+        if [ -f "${backup}/${opt}" ] || [ -f "${backup}/no_${opt}" ]; then
+            eval "c_$opt=\"${backup}/$opt\""
         else
-            eval c_$opt=\"${CDEFAULTS}/$opt\"
+            eval "c_$opt=\"${CDEFAULTS}/$opt\""
         fi
     done
 
@@ -599,6 +611,8 @@ while [ "${source_no}" -lt "${no_sources}" ]; do
     #
     # Sort by ctime (default) or mtime (configuration option)
     #
+    # variable is assigned using eval
+    # shellcheck disable=SC2154
     if [ -f "${c_mtime}" ] ; then
         TSORT="t"
     else
@@ -642,6 +656,8 @@ while [ "${source_no}" -lt "${no_sources}" ]; do
     #
     # Exclude list
     #
+    # variable is assigned using eval
+    # shellcheck disable=SC2154
     if [ -f "${c_exclude}" ]; then
         set -- "$@" "--exclude-from=${c_exclude}"
     fi
@@ -649,6 +665,8 @@ while [ "${source_no}" -lt "${no_sources}" ]; do
     #
     # Output a summary
     #
+    # variable is assigned using eval
+    # shellcheck disable=SC2154
     if [ -f "${c_summary}" ]; then
         set -- "$@" "--stats"
     fi
@@ -657,6 +675,8 @@ while [ "${source_no}" -lt "${no_sources}" ]; do
     # Verbosity for rsync, rm, and mkdir
     #
     VVERBOSE=""
+    # variable is assigned using eval
+    # shellcheck disable=SC2154
     if [ -f "${c_very_verbose}" ]; then
         set -- "$@" "-vv"
         VVERBOSE="-v"
@@ -667,8 +687,10 @@ while [ "${source_no}" -lt "${no_sources}" ]; do
     #
     # Extra options for rsync provided by the user
     #
+    # variable is assigned using eval
+    # shellcheck disable=SC2154
     if [ -f "${c_rsync_options}" ]; then
-        while read line; do
+        while read -r line; do
             # Trim line.
             ln=$(echo "${line}" | awk '{$1=$1;print;}')
             # Only if ln is non zero length string.
@@ -687,6 +709,8 @@ while [ "${source_no}" -lt "${no_sources}" ]; do
     # Check: source is up and accepting connections (before deleting old backups!)
     #
     if ! rsync "$@" "${source}" >/dev/null 2>"${TMP}" ; then
+        # variable is assigned using eval
+        # shellcheck disable=SC2154
         if [ ! -f "${c_quiet_if_down}" ]; then
             cat "${TMP}"
         fi
@@ -706,10 +730,13 @@ while [ "${source_no}" -lt "${no_sources}" ]; do
     #
     # Check incomplete backups (needs echo to remove newlines)
     #
+    # shellcheck disable=SC2010
     ls -1 | grep "${CMARKER}\$" > "${TMP}"; ret=$?
 
     if [ "$ret" -eq 0 ]; then
-        _techo "Incomplete backups: $(echo $(cat "${TMP}"))"
+        _techo "Incomplete backups: $(cat "${TMP}")"
+        # variable is assigned using eval
+        # shellcheck disable=SC2154
         if [ -f "${c_delete_incomplete}" ]; then
             delete_from_file "${TMP}" "${CMARKER}" &
         fi
@@ -718,12 +745,15 @@ while [ "${source_no}" -lt "${no_sources}" ]; do
     #
     # Include current time in name, not the time when we began to remove above
     #
-    export destination_name="${INTERVAL}.$(${CDATE}).$$-${source_no}"
-    export destination_dir="${ddir}/${destination_name}"
+    destination_name="${INTERVAL}.$(${CDATE}).$$-${source_no}"
+    export destination_name
+    destination_dir="${ddir}/${destination_name}"
+    export destination_dir
 
     #
     # Check: maximum number of backups is reached?
     #
+    # shellcheck disable=SC2010
     count="$(ls -1 | grep -c "^${INTERVAL}\\.")"
 
     _techo "Existing backups: ${count} Total keeping backups: ${c_interval}"
@@ -731,6 +761,7 @@ while [ "${source_no}" -lt "${no_sources}" ]; do
     if [ "${count}" -ge "${c_interval}" ]; then
         # Use oldest directory as new backup destination directory.
         # It need not to be deleted, rsync will sync its content.
+        # shellcheck disable=SC2010
         oldest_bak=$(ls -${TSORT}1r | grep "^${INTERVAL}\\." | head -n 1 || \
             _exit_err "Listing oldest backup failed")
         _techo "Using ${oldest_bak} for destination dir ${destination_dir}"
@@ -739,14 +770,15 @@ while [ "${source_no}" -lt "${no_sources}" ]; do
             touch "${destination_dir}"
 
             # We have something to remove only if count > interval.
-            remove="$((${count} - ${c_interval}))"
+            remove="$((count - c_interval))"
         else
             _techo_err "Renaming oldest backup ${oldest_bak} to ${destination_dir} failed, removing it."
-            remove="$((${count} - ${c_interval} + 1))"
+            remove="$((count - c_interval + 1))"
         fi
         if [ "${remove}" -gt 0 ]; then
             _techo "Removing ${remove} backup(s)..."
 
+            # shellcheck disable=SC2010
             ls -${TSORT}1r | grep "^${INTERVAL}\\." | head -n "${remove}" > "${TMP}" || \
                     _exit_err "Listing old backups failed"
 
@@ -760,6 +792,7 @@ while [ "${source_no}" -lt "${no_sources}" ]; do
     # oldest existing destination directory.
     #
     dest_dir_name=$(basename "${destination_dir}")
+    # shellcheck disable=SC2010
     last_dir="$(ls -${TSORT}p1 | grep '/$' | grep -v "${dest_dir_name}" | head -n 1)" || \
         _exit_err "Failed to list contents of ${ddir}."
 
@@ -793,8 +826,10 @@ while [ "${source_no}" -lt "${no_sources}" ]; do
     # Check if rsync exit code indicates failure.
     #
     fail=""
+    # variable is assigned using eval
+    # shellcheck disable=SC2154
     if [ -f "$c_rsync_failure_codes" ]; then
-        while read code ; do
+        while read -r code ; do
             if [ "$ret" = "$code" ]; then
                 fail=1
             fi
@@ -831,10 +866,10 @@ while [ "${source_no}" -lt "${no_sources}" ]; do
     # Time calculation
     #
     end_s="$(${SDATE})"
-    full_seconds="$((${end_s} - ${begin_s}))"
-    hours="$((${full_seconds} / 3600))"
-    minutes="$(((${full_seconds} % 3600) / 60))"
-    seconds="$((${full_seconds} % 60))"
+    full_seconds="$((end_s - begin_s))"
+    hours="$((full_seconds / 3600))"
+    minutes="$(((full_seconds % 3600) / 60))"
+    seconds="$((full_seconds % 60))"
 
     _techo "Backup lasted: ${hours}:${minutes}:${seconds} (h:m:s)"