Wordcount程序是Hadoop上的经典“HelloWorld”程序。CDH系统自带了wordcount程序来检测部署的成功与否。

# 解压提前准备好的莎士比亚全集
[sujx@elephant ~]$ gzip -d shakespeare.txt.gz

# 上传至hadoop文件系统
[sujx@elephant ~]$ hdfs dfs -mkdir /user/sujx/input
[sujx@elephant ~]$ hdfs dfs -put shakespeare.txt /user/sujx/input

# 查看有哪些测试程序可用
[sujx@elephant ~]$ hadoop jar /opt/cloudera/parcels/CDH/lib/hadoop-mapreduce/hadoop-mapreduce-examples.jar
An example program must be given as the first argument.
Valid program names are:
  aggregatewordcount: An Aggregate based map/reduce program that counts the words in the input files.
  aggregatewordhist: An Aggregate based map/reduce program that computes the histogram of the words in the input files.
  bbp: A map/reduce program that uses Bailey-Borwein-Plouffe to compute exact digits of Pi.  dbcount: An example job that count the pageview counts from a database.
  distbbp: A map/reduce program that uses a BBP-type formula to compute exact bits of Pi.    grep: A map/reduce program that counts the matches of a regex in the input.
  join: A job that effects a join over sorted, equally partitioned datasets
  multifilewc: A job that counts words from several files.
  pentomino: A map/reduce tile laying program to find solutions to pentomino problems.       pi: A map/reduce program that estimates Pi using a quasi-Monte Carlo method.
  randomtextwriter: A map/reduce program that writes 10GB of random textual data per node.   randomwriter: A map/reduce program that writes 10GB of random data per node.
  secondarysort: An example defining a secondary sort to the reduce.
  sort: A map/reduce program that sorts the data written by the random writer.
  sudoku: A sudoku solver.
  teragen: Generate data for the terasort
  terasort: Run the terasort
  teravalidate: Checking results of terasort
  wordcount: A map/reduce program that counts the words in the input files.
  wordmean: A map/reduce program that counts the average length of the words in the input files.
  wordmedian: A map/reduce program that counts the median length of the words in the input files.
  wordstandarddeviation: A map/reduce program that counts the standard deviation of the length of the words in the input files.

# 执行mapreduce运算，output文件夹会自动建立
[sujx@elephant ~]$ hadoop jar /opt/cloudera/parcels/CDH/lib/hadoop-mapreduce/hadoop-mapreduce-examples.jar wordcount /user/sujx/input/shakespeare.txt /user/sujx/output/

# 查看输出结果
[sujx@elephant ~]$ hdfs dfs -ls /user/sujx/output
Found 4 items
-rw-r--r--   3 sujx supergroup          0 2020-03-09 02:47 /user/sujx/output/_SUCCESS      -rw-r--r--   3 sujx supergroup     238211 2020-03-09 02:47 /user/sujx/output/part-r-00000  -rw-r--r--   3 sujx supergroup     236617 2020-03-09 02:47 /user/sujx/output/part-r-00001  -rw-r--r--   3 sujx supergroup     238668 2020-03-09 02:47 /user/sujx/output/part-r-00002 

# 查看输出内容
[sujx@elephant ~]$ hdfs dfs -tail /user/sujx/output/part-r-00000
.       3
writhled        1
writing,        4
writings.       1
writs   1
written,        3
wrong   112
wrong'd-        1
wrong-should    1
wrong.  39
wrong:  1
wronged 11
wronged.        3
wronger,        1
wronger;        1
wrongfully?     1
wrongs  40
wrongs, 9
wrongs; 9
wrote?  1
wrought,        4
…………