How to replace ${} placeholders in a text file?


Question

I want to pipe the output of a "template" file into MySQL, the file having variables like ${dbName} interspersed. What is the command line utility to replace these instances and dump the output to standard output?

1
129
11/3/2015 8:06:52 PM

Accepted Answer

Sed!

Given template.txt:

The number is ${i}
The word is ${word}

we just have to say:

sed -e "s/\${i}/1/" -e "s/\${word}/dog/" template.txt

Thanks to Jonathan Leffler for the tip to pass multiple -e arguments to the same sed invocation.

154
1/7/2016 1:49:01 PM

Update

Here is a solution from yottatsa on a similar question that only does replacement for variables like $VAR or ${VAR}, and is a brief one-liner

i=32 word=foo envsubst < template.txt

Of course if i and word are in your environment, then it is just

envsubst < template.txt

On my Mac it looks like it was installed as part of gettext and from MacGPG2

Old Answer

Here is an improvement to the solution from mogsie on a similar question, my solution does not require you to escale double quotes, mogsie's does, but his is a one liner!

eval "cat <<EOF
$(<template.txt)
EOF
" 2> /dev/null

The power on these two solutions is that you only get a few types of shell expansions that don't occur normally $((...)), `...`, and $(...), though backslash is an escape character here, but you don't have to worry that the parsing has a bug, and it does multiple lines just fine.


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