Apache > Hadoop > Pig
 

Shell and Utility Commands

Shell Commands

fs

Invokes any FsShell command from within a Pig script or the Grunt shell.

Syntax

fs subcommand subcommand_parameters

Terms

subcommand

The FsShell command.

subcommand_parameters

The FsShell command parameters.

Usage

Use the fs command to invoke any FsShell command from within a Pig script or Grunt shell. The fs command greatly extends the set of supported file system commands and the capabilities supported for existing commands such as ls that will now support globing. For a complete list of FsShell commands, see File System Shell Guide

Examples

In these examples a directory is created, a file is copied, a file is listed.

fs -mkdir /tmp
fs -copyFromLocal file-x file-y
fs -ls file-y

sh

Invokes any sh shell command from within a Pig script or the Grunt shell.

Syntax

sh subcommand subcommand_parameters

Terms

subcommand

The sh shell command.

subcommand_parameters

The sh shell command parameters.

Usage

Use the sh command to invoke any sh shell command from within a Pig script or Grunt shell.

Note that only real programs can be run form the sh command. Commands such as cd are not programs but part of the shell environment and as such cannot be executed unless the user invokes the shell explicitly, like "bash cd".

Example

In this example the ls command is invoked.

grunt> sh ls 
bigdata.conf 
nightly.conf 
..... 
grunt> 

Utility Commands

clear

Clear the screen of Pig grunt shell and position the cursor at top of the screen.

Syntax

clear

Terms

key

Description.

none

no parameters

Example

In this example the clear command clean up Pig grunt shell.

grunt> clear

exec

Run a Pig script.

Syntax

exec [–param param_name = param_value] [–param_file file_name] [script] 

Terms

–param param_name = param_value

See Parameter Substitution.

–param_file file_name

See Parameter Substitution.

script

The name of a Pig script.

Usage

Use the exec command to run a Pig script with no interaction between the script and the Grunt shell (batch mode). Aliases defined in the script are not available to the shell; however, the files produced as the output of the script and stored on the system are visible after the script is run. Aliases defined via the shell are not available to the script.

With the exec command, store statements will not trigger execution; rather, the entire script is parsed before execution starts. Unlike the run command, exec does not change the command history or remembers the handles used inside the script. Exec without any parameters can be used in scripts to force execution up to the point in the script where the exec occurs.

For comparison, see the run command. Both the exec and run commands are useful for debugging because you can modify a Pig script in an editor and then rerun the script in the Grunt shell without leaving the shell. Also, both commands promote Pig script modularity as they allow you to reuse existing components.

Examples

In this example the script is displayed and run.

grunt> cat myscript.pig
a = LOAD 'student' AS (name, age, gpa);
b = LIMIT a 3;
DUMP b;

grunt> exec myscript.pig
(alice,20,2.47)
(luke,18,4.00)
(holly,24,3.27)

In this example parameter substitution is used with the exec command.

grunt> cat myscript.pig
a = LOAD 'student' AS (name, age, gpa);
b = ORDER a BY name;

STORE b into '$out';

grunt> exec –param out=myoutput myscript.pig

In this example multiple parameters are specified.

grunt> exec –param p1=myparam1 –param p2=myparam2 myscript.pig

help

Prints a list of Pig commands or properties.

Syntax

-help [properties]  

Terms

properties

List Pig properties.

Usage

The help command prints a list of Pig commands or properties.

Example

Use "-help" to get a list of commands.

$ pig -help

Apache Pig version 0.8.0-dev (r987348)
compiled Aug 19 2010, 16:38:44

USAGE: Pig [options] [-] : Run interactively in grunt shell.
       Pig [options] -e[xecute] cmd [cmd ...] : Run cmd(s).
       Pig [options] [-f[ile]] file : Run cmds found in file.
  options include:
    -4, -log4jconf - Log4j configuration file, overrides log conf
    -b, -brief - Brief logging (no timestamps)
    -c, -check - Syntax check
etc …

Use "-help properties" to get a list of properties.

$ pig -help properties

The following properties are supported:
    Logging:
        verbose=true|false; default is false. This property is the same as -v switch
        brief=true|false; default is false. This property is the same as -b switch
        debug=OFF|ERROR|WARN|INFO|DEBUG; default is INFO. This property is the same as -d switch
        aggregate.warning=true|false; default is true. If true, prints count of warnings
            of each type rather than logging each warning.
etc …

history

Display the list of statements used so far.

Syntax

history [-n]

Terms

key

Description.

-n

Omit line numbers in the list.

Usage

The history command shows the statements used so far.

Example

In this example the history command shows all the statements with line numbers and without them.

grunt> a = LOAD 'student' AS (name, age, gpa);
grunt> b = order a by name;
grunt> history
1 a = LOAD 'student' AS (name, age, gpa);
2 b = order a by name;

grunt> c = order a by name;
grunt> history -n
a = LOAD 'student' AS (name, age, gpa);
b = order a by name;
c = order a by name;

kill

Kills a job.

Syntax

kill jobid

Terms

jobid

The job id.

Usage

Use the kill command to kill a Pig job based on the job id.

The kill command will attempt to kill any MapReduce jobs associated with the Pig job. Under certain conditions, however, this may fail; for example, when a Pig job is killed and does not have a chance to call its shutdown procedures.

Example

In this example the job with id job_0001 is killed.

grunt> kill job_0001

quit

Quits from the Pig grunt shell.

Syntax

exit

Terms

none

no parameters

Usage

The quit command enables you to quit or exit the Pig grunt shell.

Example

In this example the quit command exits the Pig grunt shall.

grunt> quit

run

Run a Pig script.

Syntax

run [–param param_name = param_value] [–param_file file_name] script 

Terms

–param param_name = param_value

See Parameter Substitution.

–param_file file_name

See Parameter Substitution.

script

The name of a Pig script.

Usage

Use the run command to run a Pig script that can interact with the Grunt shell (interactive mode). The script has access to aliases defined externally via the Grunt shell. The Grunt shell has access to aliases defined within the script. All commands from the script are visible in the command history.

With the run command, every store triggers execution. The statements from the script are put into the command history and all the aliases defined in the script can be referenced in subsequent statements after the run command has completed. Issuing a run command on the grunt command line has basically the same effect as typing the statements manually.

For comparison, see the exec command. Both the run and exec commands are useful for debugging because you can modify a Pig script in an editor and then rerun the script in the Grunt shell without leaving the shell. Also, both commands promote Pig script modularity as they allow you to reuse existing components.

Example

In this example the script interacts with the results of commands issued via the Grunt shell.

grunt> cat myscript.pig
b = ORDER a BY name;
c = LIMIT b 10;

grunt> a = LOAD 'student' AS (name, age, gpa);

grunt> run myscript.pig

grunt> d = LIMIT c 3;

grunt> DUMP d;
(alice,20,2.47)
(alice,27,1.95)
(alice,36,2.27)

In this example parameter substitution is used with the run command.

grunt> a = LOAD 'student' AS (name, age, gpa);

grunt> cat myscript.pig
b = ORDER a BY name;
STORE b into '$out';

grunt> run –param out=myoutput myscript.pig

set

Assigns values to keys used in Pig.

Syntax

set key 'value'

Terms

key

Key (see table). Case sensitive.

value

Value for key (see table). Case sensitive.

Usage

Use the set command to assign values to keys, as shown in the table. All keys and their corresponding values (for Pig and Hadoop) are case sensitive.

Key

Value

Description

default_parallel

a whole number

Sets the number of reducers for all MapReduce jobs generated by Pig (see Use the Parallel Features).

debug

on/off

Turns debug-level logging on or off.

job.name

Single-quoted string that contains the job name.

Sets user-specified name for the job

job.priority

Acceptable values (case insensitive): very_low, low, normal, high, very_high

Sets the priority of a Pig job.

stream.skippath

String that contains the path.

For streaming, sets the path from which not to ship data (see DEFINE (UDFs, streaming) and About Auto-Ship).

All Pig and Hadoop properties can be set, either in the Pig script or via the Grunt command line.

Examples

In this example key value pairs are set at the command line.

grunt> SET debug 'on'
grunt> SET job.name 'my job'
grunt> SET default_parallel 100

In this example default_parallel is set in the Pig script; all MapReduce jobs that get launched will use 20 reducers.

SET default_parallel 20;
A = LOAD 'myfile.txt' USING PigStorage() AS (t, u, v);
B = GROUP A BY t;
C = FOREACH B GENERATE group, COUNT(A.t) as mycount;
D = ORDER C BY mycount;
STORE D INTO 'mysortedcount' USING PigStorage();

In this example multiple key value pairs are set in the Pig script. These key value pairs are put in job-conf by Pig (making the pairs available to Pig and Hadoop). This is a script-wide setting; if a key value is defined multiple times in the script the last value will take effect and will be set for all jobs generated by the script.

...
SET mapred.map.tasks.speculative.execution false; 
SET pig.logfile mylogfile.log; 
SET my.arbitrary.key my.arbitary.value; 
...