Can we use shell variables in awk?

Question

Can we use shell variables in AWK like $VAR instead of $1, $2? For example:

UL=(AKHIL:AKHIL_NEW,SWATHI:SWATHI_NEW)  NUSR=`echo ${UL[*]}|awk -F, '{print NF}'` echo $NUSR echo ${UL[*]}|awk -F, '{print $NUSR}' 

Actually am an oracle DBA we get lot of import requests. I'm trying to automate it using the script. The script will find out the users in the dump and prompt for the users to which dump needs to be loaded.

Suppose the dumps has two users AKHIL, SWATHI (there can be may users in the dump and i want to import more number of users). I want to import the dumps to new users AKHIL_NEW and SWATHI_NEW. So the input to be read some think like AKHIL:AKHIL_NEW,SWATHI:SWATHI_NEW.

First, I need to find the Number of users to be created, then I need to get new users i.e. AKHIL_NEW,SWATHI_NEW from the input we have given. So that I can connect to the database and create the new users and then import. I'm not copying the entire code: I just copied the code from where it accepts the input users.

UL=(AKHIL:AKHIL_NEW,SWATHI:SWATHI_NEW) ## it can be many users like     USER1:USER1_NEW,USER2_USER2_NEW,USER3:USER_NEW..  NUSR=`echo ${UL[*]}|awk -F, '{print NF}'` #finding  number of fields or users y=1 while [ $y -le $NUSR ] ; do     USER=`echo ${UL[*]}|awk -F, -v NUSR=$y  '{print $NUSR}' |awk -F: '{print $2}'` #getting     Users to created AKHIL_NEW and SWATHI_NEW and passing to SQLPLUS     if [[ $USER = SCPO* ]]; then         TBS=SCPODATA     else         if [[ $USER = WWF* ]]; then             TBS=WWFDATA         else             if [[ $USER = STSC* ]]; then                 TBS=SCPODATA             else                 if [[ $USER = CSM* ]]; then                     TBS=CSMDATA                 else                     if [[ $USER = TMM* ]]; then                         TBS=TMDATA                     else                         if [[ $USER = IGP* ]]; then                         TBS=IGPDATA                         fi                     fi                 fi              fi         fi     fi      sqlplus -s '/ as sysdba'  <<EOF   # CREATING the USERS in the database      CREATE USER $USER IDENTIFIED BY $USER  DEFAULT TABLESPACE $TBS TEMPORARY TABLESPACE TEMP QUOTA 0K on SYSTEM QUOTA UNLIMITED ON $TBS;      GRANT     CONNECT,        CREATE TABLE,        CREATE VIEW,        CREATE SYNONYM,        CREATE SEQUENCE,        CREATE DATABASE LINK,        RESOURCE,        SELECT_CATALOG_ROLE     to $USER;     EOF      y=`expr $y + 1` done  impdp sysem/manager DIRECTORY=DATA_PUMP DUMPFILE=imp.dp logfile=impdp.log SCHEMAS=AKHIL,SWATHI REMPA_SCHEMA=${UL[*]}  

In the last impdp command I need to get the original users in the dumps i.e AKHIL,SWATHI using the variables.

Answer 1

Yes, you can use the shell variables inside awk. There are a bunch of ways of doing it, but my favorite is to define a variable with the -v flag:

$ echo | awk -v my_var=4 '{print "My var is " my_var}' My var is 4 

Just pass the environment variable as a parameter to the -v flag. For example, if you have this variable:

$ VAR=3 $ echo $VAR 3 

Use it this way:

$ echo | awk -v env_var="$VAR" '{print "The value of VAR is " env_var}' The value of VAR is 3 

Of course, you can give the same name, but the $ will not be necessary:

$ echo | awk -v VAR="$VAR" '{print "The value of VAR is " VAR}' The value of VAR is 3 

A note about the $ in awk: unlike bash, Perl, PHP etc., it is not part of the variable's name but instead an operator.

Answer 2

Awk and Gawk provide the ENVIRON associative array that holds all exported environment variables. So in your awk script you can use ENVIRON["VarName"] to get the value of VarName, provided that VarName has been exported before running awk.

Note ENVIRON is a predefined awk variable NOT a shell environment variable.

Since I don't have enough reputation to comment on the other answers I have to include them here!

The earlier answer showing $ENVIRON is incorrect - that syntax would be expanded by the shell, and probably result in expanding to nothing.

Further earlier comments about C not being able to access environment variable is wrong. Contrary to what is said above, C (and C++) can access environment variables using the getenv("VarName") function. Many other languages provide similar access (e.g., Java: System.getenv(), Python: os.environ, Haskell System.Environment, ...). Note in all cases access to environment variables is read-only, you cannot change an environment variable in a program and get that value back to the calling script.