diff --git a/record_m3u8.sh b/record_m3u8.sh
index a2b5641..1cececf 100644
--- a/record_m3u8.sh
+++ b/record_m3u8.sh
@@ -1,7 +1,7 @@
 #!/bin/bash
 # General m3u8 Live Stream Recorder
 
-if [ ! -n "$1" ]; then
+if [[ ! -n "$1" ]]; then
   echo "usage: $0 m3u8_url [loop]"
   exit 1
 fi
@@ -11,7 +11,7 @@ while true; do
   FNAME="stream_$(date +"%Y%m%d_%H%M%S").ts"
   ffmpeg -i "$1" -codec copy -f mpegts "$FNAME"
 
-  [ "$2" != "loop" ] && break
+  [[ "$2" != "loop" ]] && break
 
   LOG_PREFIX=$(date +"[%Y-%m-%d %H:%M:%S]")
   echo "$LOG_PREFIX The stream is not available now."
diff --git a/record_openrec.sh b/record_openrec.sh
index 55d7aa4..71a8971 100644
--- a/record_openrec.sh
+++ b/record_openrec.sh
@@ -1,7 +1,7 @@
 #!/bin/bash
 # OPENREC.tv Live Stream Recorder
 
-if [ ! -n "$1" ]; then
+if [[ ! -n "$1" ]]; then
   echo "usage: $0 openrec_id [format] [loop|once]"
   exit 1
 fi
@@ -19,7 +19,7 @@ while true; do
     LIVE_URL=$(curl -s "https://www.openrec.tv/user/$1" |\
       grep -Eoi "href=\"https://www.openrec.tv/live/(.+)\" class" |\
       head -n 1 | cut -d '"' -f 2)
-    [ -n "$LIVE_URL" ] && break
+    [[ -n "$LIVE_URL" ]] && break
 
     echo "$LOG_PREFIX The stream is not available now."
     echo "$LOG_PREFIX Retry after 30 seconds..."
@@ -40,5 +40,5 @@ while true; do
   # Exit if we just need to record current stream
   LOG_PREFIX=$(date +"[%Y-%m-%d %H:%M:%S]")
   echo "$LOG_PREFIX Live stream recording stopped."
-  [ "$3" == "once" ] && break
+  [[ "$3" == "once" ]] && break
 done
diff --git a/record_twitcast.sh b/record_twitcast.sh
index c323953..ee07811 100644
--- a/record_twitcast.sh
+++ b/record_twitcast.sh
@@ -1,7 +1,7 @@
 #!/bin/bash
 # TwitCasting Live Stream Recorder
 
-if [ ! -n "$1" ]; then
+if [[ ! -n "$1" ]]; then
   echo "usage: $0 twitcasting_id [loop|once]"
   exit 1
 fi
@@ -32,5 +32,5 @@ while true; do
   # Exit if we just need to record current stream
   LOG_PREFIX=$(date +"[%Y-%m-%d %H:%M:%S]")
   echo "$LOG_PREFIX Live stream recording stopped."
-  [ "$2" == "once" ] && break
+  [[ "$2" == "once" ]] && break
 done
diff --git a/record_twitch.sh b/record_twitch.sh
index e22f14f..43916fa 100644
--- a/record_twitch.sh
+++ b/record_twitch.sh
@@ -1,7 +1,7 @@
 #!/bin/bash
 # Twitch Live Stream Recorder
 
-if [ ! -n "$1" ]; then
+if [[ ! -n "$1" ]]; then
   echo "usage: $0 twitch_id [format] [loop|once]"
   exit 1
 fi
@@ -35,5 +35,5 @@ while true; do
   # Exit if we just need to record current stream
   LOG_PREFIX=$(date +"[%Y-%m-%d %H:%M:%S]")
   echo "$LOG_PREFIX Live stream recording stopped."
-  [ "$3" == "once" ] && break
+  [[ "$3" == "once" ]] && break
 done
diff --git a/record_youtube.sh b/record_youtube.sh
index 522e36c..e7a121a 100644
--- a/record_youtube.sh
+++ b/record_youtube.sh
@@ -1,14 +1,13 @@
 #!/bin/bash
 # YouTube Live Stream Recorder
 
-if [ ! -n "$1" ]; then
+if [[ ! -n "$1" ]]; then
   echo "usage: $0 youtube_channel_id|live_url [format] [loop|once]"
   exit 1
 fi
 
 # Construct full URL if only channel id given
 LIVE_URL=$1
-# Use double square brackets construct here to test substring
 [[ "$1" == "http"* ]] || LIVE_URL="https://www.youtube.com/channel/$1/live"
 
 # Record the best format available but not better that 720p by default
@@ -26,7 +25,7 @@ while true; do
     M3U8_URL=$(youtube-dl -g -f "$FORMAT" \
       --no-playlist --playlist-items 1 \
       --match-filter is_live "$LIVE_URL" 2>/dev/null)
-    [ -n "$M3U8_URL" ] && break
+    [[ -n "$M3U8_URL" ]] && break
 
     echo "$LOG_PREFIX The stream is not available now."
     echo "$LOG_PREFIX Retry after 30 seconds..."
@@ -52,5 +51,5 @@ while true; do
   # Exit if we just need to record current stream
   LOG_PREFIX=$(date +"[%Y-%m-%d %H:%M:%S]")
   echo "$LOG_PREFIX Live stream recording stopped."
-  [ "$3" == "once" ] && break
+  [[ "$3" == "once" ]] && break
 done