在Linux檔案系統中，Shell指令碼判斷某個檔案是否存在：

# 這裡的-f引數判斷$file是否存在 
if [ ! -f "$file" ]; then
　　echo "檔案不存在!"
fi

Hadoop提供了test命令判斷HDFS上某個檔案或目錄是否存在：

[[email protected] ~]# hdfs dfs -help
...
-test -[defsz] <path> :
  Answer various questions about <path>, with result via exit status.
    -d  return
 
 0 if <path> is a directory.
    -e  return 0 if <path> exists.
    -f  return 0 if <path> is a file.
    -s  return 0 if file <path> is greater than zero bytes in size.
    -z  return 0 if file <path> is zero bytes in size, else return 1.
...

用test命令來判斷某個檔案或目錄是否存在。如果檔案或目錄存在，返回0；反之返回1。

[[email protected] ~]# hdfs dfs -test -e /path/not/exist
[[email protected] ~]# echo $?
1
[[email protected] ~]# hdfs dfs -test -e /path/exist
[[email protected] ~]# echo $?
0
[[email protected] ~]# 

那麼我們可以在Shell腳本里面判斷HDFS上某個檔案是否存在：

#!/bin/bash
hdfs dfs -test -e /path/exist
if [ $?
 
 -eq 0 ] ;then 
    echo 'exist' 
else 
    echo 'Error! NO Such File Or Directory !' 
fi
...

test 命令還可以判斷:**

1. -d某個路徑是否是資料夾( -d);
2. -f某個路徑是否是檔案( -f);
3. -s某個檔案大小是否大於0;
4. -z某個檔案大小等於0

#!/bin/bash

#判斷是否是資料夾
hdfs dfs -test -d /path/exist
if [ $? -eq 0 ] ;then 
    echo 'Is a directory' 
else 
    echo 'Is not a directory' 
fi

#判斷是否是檔案
hdfs dfs -test -f /path/exist
if [ $? -eq 0 ] ;then 
    echo 'Is a file' 
else 
    echo 'Is not a file' 
fi

#判斷檔案大小是否大於0
hdfs dfs -test -s /path/exist
if [ $? -eq 0 ] ;then 
    echo 'Is greater than zero bytes in size' 
else 
    echo 'Is not greater than zero bytes in size' 
fi
 
#判斷檔案大小是否等於0
hdfs dfs -test -z /path/exist
if [ $? -eq 0 ] ;then 
    echo 'Is zero bytes in size.' 
else 
    echo 'Is not zero bytes in size. '
fi