Regarding .sh and variable declaration

shivaa · 04-02-2013, 08:59 AM

It looks a text file more than a script. Since no command(s) are specified in it, so it's won't do anything. There is no scope of these variables outside of script.

If you want to create directories, write following commands at the end of your script, like this:

Code:

#!/bin/bash
........
........
# Hadoop Service - HDFS
 #
# Space separated list of directories where NameNode will store file system image.
 DFS_NAME_DIR="/grid/hadoop/hdfs/namenode /grid1/hadoop/hdfs/namenode"

# Space separated list of directories where DataNodes will store the blocks.
 DFS_DATA_DIR="/grid/hadoop/hdfs/datanode /grid1/hadoop/hdfs/datanode /grid2/hadoop/hdfs/datanode"
........
........ 
mkdir -p $DFS_NAME_DIR
chmod -R 755 $DFS_NAME_DIR
echo "Directories $DFS_NAME_DIR created."

chrism01 · 04-02-2013, 07:13 PM

As above, vars go out of scope when a script completes, so either

1. add your cmds to the bottom as above
OR
2. source the file so it actually sets the vars in your current env eg

Code:

. ./script

#OR
source ./script

then do your mkdir etc.

turboscrew · 04-03-2013, 12:18 AM

Like I mentioned:

Quote:

Originally Posted by rushikeshgaradade

DFS_NAME_DIR="/grid/hadoop/hdfs/namenode /grid1/hadoop/hdfs/namenode"

Here a new shell is started to run the command. The variable "DFS_NAME_DIR" becomes defined in this shell's environment. When the script ends, the shell exits and the environment is gone. You can see that by adding "printenv | grep DFS_NAME_DIR" to the end of the script.
Then give that same command on the terminal after the script is done.

If you want that variable to be seen in your command-shell, you have to "source" the script
("." is shorthand for "source").

Code:

source my_script.sh
. my_script.sh

Quote:

i have executed it with
#bash dierctories.sh

but i didnt find any affect of it

If you had the variable defined in this shell's environment, the shell executing your
script "directories.sh" doesn't have that variable in its environment unless the variable is exported.

Code:

export DFS_NAME_DIR="/grid/hadoop/hdfs/namenode /grid1/hadoop/hdfs/namenode"

Exported variables are "forwarded" to "sub-shells".

Quote:

and also it is said

mkdir -p $DFS_NAME_DIR

but this command showing error:

mkdir: missing operand
Try `mkdir --help' for more information.

Does this mean that directories.sh file is not executed. or is there any other alternative for "DFS_NAME_DIR"

Please help me.........

That's why there is no variable "DFS_NAME_DIR" in your shell environment and the command:
"mkdir -p $DFS_NAME_DIR" becomes "mkdir -p"

rushikesh24 · 04-03-2013, 01:22 AM

thanks...

actually i need these variables outside the scripts also....
i have to execute the commands like mkdir -p DFS_NAME_DIR etc.
As u said these variables don't hold the values after running the scripts... So can we make the variables to hold the values permanently i.e. outside the scripts also.

shivaa · 04-03-2013, 01:39 AM

Quote:

Originally Posted by rushikesh24

As u said these variables don't hold the values after running the scripts... So can we make the variables to hold the values permanently i.e. outside the scripts also.

Did you read the above posts? I don't think so. If you want those variables outside of your script, then use following cmds:

Code:

~$ source myscript.sh
OR
~$ . myscript.sh

evo2 · 04-03-2013, 01:43 AM

Hi,

Quote:

Originally Posted by rushikesh24

So can we make the variables to hold the values permanently i.e. outside the scripts also.

Yes, as explained by others you do this by sourcing the script instead of executing it.
Eg instead of running:

Code:

foo.sh

you need

Code:

source foo.sh

or

Code:

. foo.sh

Note however that if you want the variables available to new processes (not just he shell you are currently in), you need to export the variables in the script. Eg

Eg Instead of

Code:

FOO="/bar/baz"

you can do

Code:

export FOO="/bar/baz"

Evo2.

rushikesh24 · 04-03-2013, 02:29 AM

hey thanks all.... n sorry.. i didnt refresh my page so didnt get new answers posted by you all..

turboscrew · 04-05-2013, 12:31 AM

Quote:

Originally Posted by evo2

Hi,

that script, as posted, does nothing but set some variables that will go out of scope as soon as it exits. Ie it does absolutely nothing. Is that really the whole script?

Evo2.

...unless it's sourced, but even then the parameters are not exported to the shells running other commands.

---------- Post added 04-05-13 at 08:32 AM ----------

"source" is a shell built-in command.
Add "export" in front of the variable definitions and source the script.
Then try running the commands.