What the need of environmental variables

Question

when we are writing shell scripts which contains sql relative statements
why we need to have these environmental variables
ORACLE_HOME=........; export ORACLE_HOME
LD_LIBRARY_PATH=$ORACLE_HOME/lib;
export LD_LIBRARY_PATH
PATH=$ORACLE_HOME/bin:$PATH;
export PATH
unset ORA_NLS33
export NLS_NUMERIC_CHARACTERS=,
please tell me
if possible each one in detail and any link contains these things

Answer 1

As already mentioned, they are pointers which allow the script to find programs and files. For example, if you set ORACLE_HOME=/app/oracle/product/10.2.0 and then PATH=$ORACLE_HOME/bin:$PATH then when you call sqlplus, the operating system can find the sqplus program because it searches down the $PATH directory structure. Some of the Oracle code itself relies on these being set - try not having ORACLE_HOME or PATH set and then executing sqlplus from the oracle installation bin directory - you get an error stating a message file cannot be accessed - this is becuse the internal code it using the ORACLE_HOME and PATH environment variables.
Also, setting the variables makes your scripts much easier to maintain - if you move your script to another server where the filesystem is different or you upgrade Oracle so that the $ORACLE_HOME changes, you only need to change these lines, rather than trawl your whole script. It's basically good coding practice to do this.
Cheers,
James