diff --git a/shell/ip.sh b/shell/ip.sh
new file mode 100644
index 0000000..20f8581
--- /dev/null
+++ b/shell/ip.sh
@@ -0,0 +1,101 @@
+#!/bin/bash
+
+
+# converts IPv4 as "A.B.C.D" to integer
+ip4_to_int() {
+  IFS=. read -r i j k l <<EOF
+$1
+EOF
+  echo $(( (i << 24) + (j << 16) + (k << 8) + l ))
+}
+
+# converts interger to IPv4 as "A.B.C.D"
+int_to_ip4() {
+  echo "$(( ($1 >> 24) % 256 )).$(( ($1 >> 16) % 256 )).$(( ($1 >> 8) % 256 )).$(( $1 % 256 ))"
+}
+
+# returns the ip part of an CIDR
+cidr_ip() {
+  IFS=/ read -r ip _ <<EOF
+$1
+EOF
+  echo $ip
+}
+
+# returns the prefix part of an CIDR
+cidr_prefix() {
+  IFS=/ read -r _ prefix <<EOF
+$1
+EOF
+  echo $prefix
+}
+
+# returns net mask in numberic from prefix size
+netmask_of_prefix() {
+  echo $((4294967295 ^ (1 << (32 - $1)) - 1))
+}
+
+# returns default gateway address (network address + 1) from CIDR
+cidr_default_gw() {
+  ip=$(ip4_to_int $(cidr_ip $1))
+  prefix=$(cidr_prefix $1)
+  netmask=$(netmask_of_prefix $prefix)
+  gw=$((ip & netmask + 1))
+  int_to_ip4 $gw
+}
+
+# returns default gateway address (broadcast address - 1) from CIDR
+cidr_default_gw_2() {
+  ip=$(ip4_to_int $(cidr_ip $1))
+  prefix=$(cidr_prefix $1)
+  netmask=$(netmask_of_prefix $prefix)
+  broadcast=$(((4294967295 - netmask) | ip))
+  int_to_ip4 $((broadcast - 1))
+}
+
+
+ip4_to_int 192.168.0.1
+# => 3232235521
+
+int_to_ip4 3232235521
+# => 192.168.0.1
+
+
+# network address
+ip=$(ip4_to_int 172.16.10.20)
+netmask=$(ip4_to_int 255.255.252.0)
+int_to_ip4 $((ip & netmask))
+# => 172.16.8.0
+
+
+# broadcast address
+ip=$(ip4_to_int 172.16.10.20)
+netmask=$(ip4_to_int 255.255.252.0)
+int_to_ip4 $(((ip & netmask) + 1))
+# => 172.16.8.1
+
+
+cidr_ip "172.16.0.10/22"
+# => 172.16.0.10
+
+cidr_prefix "172.16.0.10/22"
+# => 22
+
+netmask_of_prefix 8
+# => 4278190080
+
+
+cidr_default_gw 192.168.10.1/24
+# => 192.168.10.1
+cidr_default_gw 192.168.10.1/16
+# => 192.168.0.1
+cidr_default_gw 172.17.18.19/20
+# => 172.17.16.1
+
+
+cidr_default_gw_2 192.168.10.1/24
+# => 192.168.10.254
+cidr_default_gw_2 192.168.10.1/16
+# => 192.168.255.254
+cidr_default_gw_2 172.17.18.19/20
+# => 172.17.31.254
\ No newline at end of file
diff --git a/shell/log.sh b/shell/log.sh
new file mode 100644
index 0000000..4ab2184
--- /dev/null
+++ b/shell/log.sh
@@ -0,0 +1,18 @@
+#!/bin/bash
+
+
+LOGFILE=log.log
+RETAIN_NUM_LINES=10
+
+function logsetup {
+    TMP=$(tail -n $RETAIN_NUM_LINES $LOGFILE 2>/dev/null) && echo "${TMP}" > $LOGFILE
+    exec > >(tee -a $LOGFILE)
+    exec 2>&1
+}
+
+function log {
+    echo "[$(date --rfc-3339=seconds)]: $*"
+}
+
+logsetup
+log hello this is a log
\ No newline at end of file