find matching name in a file using variable 1 and replace using variable 2 shell

Question

My oratab file has following content:

cat /etc/oratab
#
# Multiple entries with the same $ORACLE_SID are not allowed.
#
#
+ASM1:/u01/app/12.2.0.1/grid:N
exaiaddb:/u02/app/oracle/product/12.2.0/dbhome_2:Y
nttest:/u02/app/oracle/product/12.2.0/dbhome_3:Y

Variable 1 : $DB_NAME=nttest

Variable 2: $DB_UNI_NAME=nttest_iad92

I simply want to find $DB_NAME in above file and replace with $DB_UNI_NAME

I tried the following, but it is not updating the file

sed -i 's/${DB_NAME}/${db_uni_name}/g' oratab

Please explain why the answers you received to yesterdays Q aren't helping you . Please update your Q above to include your best attempt at solving your problem, or we'll just think you can't be bothered. Good luck. — shellter
– shellter, Commented Oct 26, 2018 at 20:34
This is replace and update the file for permanent change. I am not sure about replacing/updating the file with new variable, so i raised this question — user918753
– user918753, Commented Oct 26, 2018 at 20:41
" Please update your Q above to include your best attempt at solving your problem" ... This sort of Q gets asked every week here. try searching for [bash] [sed] use shell variables. Good luck. — shellter
– shellter, Commented Oct 26, 2018 at 20:47
sed -i 's/${DB_NAME}/${db_uni_name}/g' oratab ... Change the single-quotes to double-quote to allow variable-expansion to take place.... Single-quotes prevent variable-expansion, so your sed command is literally looking for the characters ${DB_NAME} (that is '$', '{', 'D', 'B', ....) in your file. — David C. Rankin
– David C. Rankin, Commented Oct 27, 2018 at 7:10

Mayank Porwal · Accepted Answer · 2018-10-27 07:06:31Z

1

The command you are using has 2 mistakes:

1.) You used the variable ${db_uni_name} in sed command. Instead, you should have used DB_UNI_NAME as you declared this above. (see difference in the case)

2.) Use double-quotes(" ") instead of single-quotes (' ') in sed command. " makes sure that sed expands the variables.

So, your command would be:

sed -i "s/${DB_NAME}/${DB_UNI_NAME}/g" oratab

This should work. Let me know.

answered Oct 27, 2018 at 7:06

Mayank Porwal

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