test

字串或文字的比對 
 Str1 = str2 | 當str1與str2相同時, 傳回True
Str1 != str2| 當str1與str2不同時, 傳回True
Str1 < Str2 
Str1 <= Str2
Str1 > Str2
Str1 >= Str2
Str | 當str不是空字符時, 傳回True
-n str | 當str的長度大於0時, 傳回True
-z str | 當str的長度是0時, 傳回True 
 [ ]與[[ ]] 差別 
 
 [ ... ] : POSIX 相容指令，別名 test，用於條件判斷式。 
 [[ ... ]] : Bash 專有語法，可用於更複雜的條件判斷式。 
 [ -n "$VAR_STR"] : 使用 [ ] 時要注意變數的雙引號用法。 
 
 範例： 
 VAR_STR=""
if [[ -n $VAR_STR ]]; then
 echo "var str is nonzero with [["
else
 echo "var str is zero with [["
fi

if [ -n $VAR_STR ]; then
 echo "var str is nonzero with ["
else
 echo "var str is zero with ["
fi 
 Output: 
 var str is zero with [[
var str is nonzero with [ 
 Fix: 
 VAR_STR=""

if [[ -n $VAR_STR ]]; then
 echo "var str is nonzero with [["
else
 echo "var str is zero with [["
fi

if [ -n "$VAR_STR" ]; then # <<<<
 echo "var str is nonzero with ["
else
 echo "var str is zero with ["
fi 
 數值型比對 
 整數 
 Int1 -eq int2 |當int1等於int2時, 傳回True
Int1 -ge int2 |當int1大於/等於int2時, 傳回True
Int1 -le int2 |當int1小於/等於int2時, 傳回True
Int1 -gt int2 |當int1大於int2時, 傳回True
Int1 -ne int2 |當int1不等於int2時, 傳回True
Int1 -lt int2 |當int1小於 int2時, 傳回True 
 浮點數 
 asr=87.22
thre=90.00
if (( $(echo "$asr < $thre" | bc -l) )); then
 return 0 # true
fi 
 檔案的比對 
 -e file | 檔案是否存在
-d file | 當file是一個目錄時, 傳回 True
-f file | 當file是一個普通檔案時, 傳回 True
-r file | 當file是一個可讀檔案時, 傳回 True
-s file | 當file檔案內容長度大於0時, 傳回 True; 空白內容傳回 False
-w file | 當file是一個可寫檔案時, 傳回 True
-x file | 當file是一個可執行檔案時, 傳回 True 
 File operators list 
 
 
 
 Operator 
 Returns 
 
 
 
 
 -a FILE 
 True if file exists. 
 
 
 -b FILE 
 True if file is block special. 
 
 
 -c FILE 
 True if file is character special. 
 
 
 -d FILE 
 True if file is a directory. 
 
 
 -e FILE 
 True if file exists. 
 
 
 -f FILE 
 True if file exists and is a regular file. 
 
 
 -g FILE 
 True if file is set-group-id. 
 
 
 -h FILE 
 True if file is a symbolic link. 
 
 
 -L FILE 
 True if file is a symbolic link. 
 
 
 -k FILE 
 True if file has its `sticky' bit set. 
 
 
 -p FILE 
 True if file is a named pipe. 
 
 
 -r FILE 
 True if file is readable by you. 
 
 
 -s FILE 
 True if file exists and is not empty. 
 
 
 -S FILE 
 True if file is a socket. 
 
 
 -t FD 
 True if FD is opened on a terminal. 
 
 
 -u FILE 
 True if the file is set-user-id. 
 
 
 -w FILE 
 True if the file is writable by you. 
 
 
 -x FILE 
 True if the file is executable by you. 
 
 
 -O FILE 
 True if the file is effectively owned by you. 
 
 
 -G FILE 
 True if the file is effectively owned by your group. 
 
 
 -N FILE 
 True if the file has been modified since it was last read. 
 
 
 ! EXPR 
 Logical not. 
 
 
 EXPR1 && EXPR2 
 Perform the and operation. 
 
 
 EXPR1 || EXPR2 
 Perform the or operation. 
 
 
 
 
 布林變數應用 
 # Let us Declare Two Boolean Variables
# Set this one to true
jobstatus=true
# Check it 
if [ "$jobstatus" = true ] ; then
	echo 'Okay :)'
else
	echo 'Noop :('
fi
# Double bracket format syntax to test Boolean variables in bash
bool=false
if [[ "$bool" = true ]] ; then
	echo 'Done.'
else
	echo 'Failed.'
fi 
 更多範例 
 # 如果前個指令執行有錯誤時，會執行兩個程序
[ ! $? -eq 0 ] && echo "Abort the process!! you can try it agian after you made change." && exit 1

# 或者
[ ! $? -eq 0 ] && {
 echo "Abort the process!! you can try it agian after you made change."
 exit 1
} 

#
if [[ $RETURN_CODE != 0 ]]; then
 echo "Zulip first start database initi failed in \"initialize-database\" exit code $RETURN_CODE. Exiting."
 exit $RETURN_CODE
fi

#
if [[ $TIMEOUT -eq 0 ]]; then
 echo "Could not connect to database server. Exiting."
 unset PGPASSWORD
 exit 1
fi
#
if (($? > 0)); then
 echo "$SECRET_KEY = $SECRET_VAR" >> "$DATA_DIR/zulip-secrets.conf"
 echo "Secret added for \"$SECRET_KEY\"."
fi
#
if test "x$newbranch" = x; then
 newbranch=`git branch -a | grep "*" | cut -d ' ' -f2`
fi

# Check router home directory.
[ -d "$PROD_HOME" ] || {
	echo "Router home directory ($PROD_HOME) not found"
	exit 1
}

# AND
autoBackupConfiguration() {
 if ([ "$AUTO_BACKUP_ENABLED" != "True" ] && [ "$AUTO_BACKUP_ENABLED" != "true" ]); then
 rm -f /etc/cron.d/autobackup
 echo "Auto backup is disabled. Continuing."
 return 0
 fi
}

# OR
if [ "$MANUAL_CONFIGURATION" = "False" ] || [ "$MANUAL_CONFIGURATION" = "false" ]; then
 databaseConfiguration
 secretsConfiguration
 authenticationBackends
 zulipConfiguration
fi

# Die if $f1 or $f2 is missing 
if [ ! -f "$f1" ] || [ ! -f "$f2" ]
then
	echo "Required files are missing."
else
	echo "Let us build SFTP jail."
fi
# And
if [[ $age -ge 18 ]] && [[ $nat -eq "Indian" ]];then
 echo "You can vote!!!"
else
 echo "You can not vote"

fi

# multiple AND
if [ -e "$DATA_DIR/.initiated" ] && ([ "$FORCE_FIRST_START_INIT" != "True" ] && [ "$FORCE_FIRST_START_INIT" != "true" ]); then
 echo "First Start Init not needed. Continuing."
 return 0
fi

# one-liner
 [[ -z "$var" ]] && echo "NULL" || echo "NOT NULL"
# if age is greater than or equal to 18 then the program will print "Adult" or it will print "Minor".
[[ $age -ge 18 ]] && echo "Adult" || echo "Minor"

# Contain a substring
if [[ $var = *pattern1* ]]; then
 echo "Do something"
fi

[[ $1 != *cyberciti.biz/faq/* ]] && { printf "Error: Specify faq url (e.g., http://www.cyberciti.biz/faq/url-1-2-3/)\n"; exit 2; }

if [[ $fullstring == *"$substr"* ]];

# Regex
if [[ $ip =~ ^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$ ]]; then

head="win00000:hascom_command.ksh : hostname:wintstc, monitor port#:17911"
if [[ $head =~ ^win00000.*$ ]]; then

# Check the the number of the version
[ "$(echo "$TMUX_VERSION >= 2.4" | bc)" = 1 ] || echo "The version $TMUX_VERSION is outdated" 
 Two functions (Is_alert & Notify) return True 
 if Is_alert && Notify; then
 echo "Send_mail"
fi