How to use a variable in a sedscript

Question

I set a variable in a shell script I then call a sed script and in the sed script I use the variable That does not seem to work and I needed help on how to achieve that

1. Following works at the command line

sed -e "s/text/$VAR" testfile

2. Following does not work

test.sh

export VAR=somevar
sed -f sedfile testfile

testfile

This is a test file

sedfile

s/text/$VAR/

Also tried

s/text/${VAR}/

Result

This is a $VAR file

Expected output

This is a somevar file

Answer 1

The soft quotes " on the command line version of your example allow for shell expansion of the variable by your shell, before sed executes the sed instructions.

The sedfile is not a shell script, it is a sed script interpreted by sed, so no shell expansion of the variable can take place. That is simply not going to work AFAIK.

Answer 2

you may wish to generate sedfile using here document syntax

cat <<foobar > sedfile
s/text1/${VAR1}/
s/text2/${ANOTHERVAR}/
foobar

• foobar must be used at the start of the line
• foobar can be any string, just use the same string in <<foobar

then do the seding

sed -f sedfile testfile

I expect your sedfile is a bit complex, for one or two substitutions it might not be worth using it.