Reading key/value parameters from a file into a shell script

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First choice: Associative array

This requires bash 4.0 or newer to support declare -A; see below for other options.

#!/bin/bash

# first, read your key/value pairs into shell variables
declare -A v=( )
while read -r var value; do
  v[$var]=$value
done < Parameters.conf

# second, perform a command that depends on them
sqlplus / as sysdba <<  E00
CREATE USER ${v[USERNAME]}
DEFAULT TABLESPACE USERS
TEMPORARY TABLESPACE TEMP
ACCOUNT UNLOCK;
ALTER USER ${v[USERNAME]} DEFAULT ROLE ALL;
GRANT CREATE SESSION TO ${v[USERNAME]};
GRANT CONNECT TO ${v[USERNAME]};
exit
E00

sqlplus / as sysdba > /home/o/output/output.log << E01
GRANT ${v[PERMISSION_TYPE]} ON ${v[TARGET_USER]}.${v[TARGET_TABLE]} TO ${v[USERNAME]};
E01

Key points:

  • Assignment to a shell variable which is itself named in a variable is described in BashFAQ #6; likewise for associative arrays.
  • The redirection needs to be done as while read key value; do ...; done <input rather than cat input | while read key value; do ...; done to avoid the bug BashFAQ #24.
  • The actual sqlplus calls shouldn’t be inside the loop, because the loop body is run once per line in the file. Since you want all the file’s lines to be read (and all the variables assigned) before running sqlplus, the loop should entirely complete before sqlplus is called.
  • Using either a prefix or an associative-array ensures that variables coming from the configuration file can’t override system environment variables like PATH or LD_PRELOAD.

Second choice: Prefixed namespace

#!/bin/bash

while read -r var value; do
  printf -v "v_$var" %s "$value"
done <Parameters.conf

# second, perform a command that depends on them
sqlplus / as sysdba <<  E00
CREATE USER ${v_USERNAME}
DEFAULT TABLESPACE USERS
TEMPORARY TABLESPACE TEMP
ACCOUNT UNLOCK;
ALTER USER ${v_USERNAME} DEFAULT ROLE ALL;
GRANT CREATE SESSION TO ${v_USERNAME};
GRANT CONNECT TO ${v_USERNAME};
exit
E00

sqlplus / as sysdba > /home/o/output/output.log << E01
GRANT ${v_PERMISSION_TYPE} ON ${v_TARGET_USER}.${v_TARGET_TABLE} TO ${v_USERNAME};
E01

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