Shell Programming and Scripting

1.) How is .profile and environment variable linked.?
2.) What happens when we execute a script.?

Answer to your first question:
When you login, the various commands in the .profile are run. This may include setting the path, the prompt, and a host of other things. An example .profile:

Code:

PATH=/usr/bin:/usr/sbin:/sbin; export PATH
MANPATH=/usr/share/man:/opt/<some_app>/man; export MANPATH
/usr/games/fortune

The above file will set the PATH and the MANPATH variables in the environment and run the fortune program. This is the way that the .profile and the env variables are linked. It is just a convenient way to customize your environment.

I didn't get the second question. I mean, when you run a script, the various commands in the script are executed. What more?

If that is so, then what is `env` used for ?

1.) where can we find the `env` file ?
2.) When we run `env` command , we find list of things. What is the use of it & How to change it .?

From the man page of env:
The simplest form of the command is to just run 'env'. This will give you the current environment, which may be used by various commands when they execute. In the more complicated form, the env command can be used to set a specified variable with the given value and that modified variable used in the environment when executing the specified command.

To understand what the above paragraph says, let us take an example (this is for ksh):

Code:

$ export ORACLE_SID=abc; export ORACLE_HOME=/oracle817
$ sqlplus internal
SQL> set pages 1000;
SQL> select name,open_mode from v$database;
NAME      OPEN_MODE
--------- ----------
ABC         MOUNTED
SQL> exit;
$ env ORACLE_SID=xyz sqlplus internal
SQL> set pages 100
SQL> select name,open_mode from v$database;
NAME      OPEN_MODE
--------- ----------
XYZ         MOUNTED
SQL> exit;
$ env|grep ORA
ORACLE_SID=abc
ORACLE_HOME=/oracle817

The above example shows how env can be used to temporarily change the environment for the duration of a single command, without actually modifying the value of the variable.

1) The 'env' command does not read from a file, the environment is stored in the memory. From the man page of environ:
2) The use of the 'list of things' that we get from the 'env' command has been explained above, to set the various environment variables, you have to use shell specific syntax.
For sh:

Code:

PATH=/usr/bin; export PATH

For ksh,bash:

Code:

export PATH=/usr/bin

For csh,tcsh:

Code:

setenv PATH /usr/bin

I think that this answers both your questions. Also, read the man pages of env and environ for more indepth explainations.
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