The tests below are test conditions provided by the shell:

    * -b file = True if the file exists and is block special file.
    * -c file = True if the file exists and is character special file.
    * -d file = True if the file exists and is a directory.
    * -e file = True if the file exists.
    * -f file = True if the file exists and is a regular file
    * -g file = True if the file exists and the set-group-id bit is set.
    * -k file = True if the files’ “sticky” bit is set.
    * -L file = True if the file exists and is a symbolic link.
    * -p file = True if the file exists and is a named pipe.
    * -r file = True if the file exists and is readable.
    * -s file = True if the file exists and its size is greater than zero.
    * -s file = True if the file exists and is a socket.
    * -t fd = True if the file descriptor is opened on a terminal.
    * -u file = True if the file exists and its set-user-id bit is set.
    * -w file = True if the file exists and is writable.
    * -x file = True if the file exists and is executable.
    * -O file = True if the file exists and is owned by the effective user id.
    * -G file = True if the file exists and is owned by the effective group id.
    * file1 -nt file2 = True if file1 is newer, by modification date, than file2.
    * file1 ot file2 = True if file1 is older than file2.
    * file1 ef file2 = True if file1 and file2 have the same device and inode numbers.
    * -z string = True if the length of the string is 0.
    * -n string = True if the length of the string is non-zero.
    * string1 = string2 = True if the strings are equal.
    * string1 != string2 = True if the strings are not equal.
    * !expr = True if the expr evaluates to false.
    * expr1 -a expr2 = True if both expr1 and expr2 are true.
    * expr1 -o expr2 = True is either expr1 or expr2 is true.

Shell中的数据问题

   ArrayName=(”element 1″ “element 2″ “element 3″)  #数组定义
   echo ${#ArrayName[@]}
  echo “The number of elements in the array is ${#ArrayName[*]}”    
   
    例子
    #!/bin/bash
    # define array
    # name server names FQDN
    NAMESERVERS=(”ns1.nixcraft.net.” “ns2.nixcraft.net.” “ns3.nixcraft.net.”)
 
    # get length of an array
     tLen=${#NAMESERVERS[@]}
 
    # use for loop read all nameservers
    for (( i=0; i<${tLen}; i++ ));
    do
      echo ${NAMESERVERS[$i]}
    done

   Sample output:

     ns1.nixcraft.net.
     ns2.nixcraft.net.
     ns3.nixcraft.net.

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