I have written small Shell/bash script, where I have some data in sampleData.txt file which I want to convert in Base64 and to pass it in variable $scriptPayload:

value=$(cat sampleData.txt)
echo "$value"
encoded= echo  $value | base64 
scriptPayload='{"scriptText":"$encoded" }'
echo "$scriptPayload"

but the output which Ii am geting is literally {"scriptText":"$encoded"}. I t should take value from $encoded variable like {"scriptText":"Test the Shell Script and its behaviour" }

Please suggest. I am new to this.


Your script has a syntax error (not actualy, but it's definitely not doing what you think it does):

encoded= echo  $value | base64 

This could, assuming you're using a shell such as bash, be written as

encoded=$( base64 <<<"$value" )

or even

encoded=$( base64 <sampleData.txt )

which captures the base64-encoding of the data in the file sampleData.txt into the variable encoded using a command substitution, in a similar way to how you're already using cat in a command substitution on your first line of code.

Since variables are not expanded within single-quoted strings, the code

scriptPayload='{"scriptText":"$encoded" }'

will not do what you think it does (it sets scriptPayload to the literal string {"scriptText":"$encoded" }).

In bash, this is better written as

printf -v scriptPayload '{"scriptText":"%s"}' "$encoded"


printf -v scriptPayload '{"scriptText":"%s"}' "$( base64 <sampleData.txt )"

The printf utility built into bash prints directly into a variable with -v varname.

Note that some base64 utility implementations may produce data with CRLF line-endings though.

Using jo:

scriptPayload=$( jo scriptText=%sampleData.txt )
printf '%s\n' "$scriptPayload"

The argument scriptText=%sampleData.txt tells jo to create a JSON object with a key scriptText. The data for that key should be the base64-encoded contents of the file sampleData.txt (it's the % that decides that it should be base64-encoded).

With a file, sampleData.txt, containing the string Hello World (followed by a newline), this would output


jo is a tool for effortlessly creating properly encoded and quoted JSON data on the command line or in shell scripts.

  • <<< in bash (like in zsh but contrary to Byron Rakitzis's clone of rc, the two shells where the feature originate from) adds a newline character (and value=$(cat sampleData.txt) strips trailing newline characters if any). You'd need printf %s "$value" | base64 Sep 28 '20 at 7:25

Your line for encoding was not doing anything, I changed it. Plus I also changed the line for the final scriptPayload and used escaping.

echo $value
encoded=`echo -n "$value" | base64`
scriptPayload="{\"scriptText\":\"${encoded}\" }"
echo $scriptPayload
encoded=`base64 -w0 < sampleData.txt`
scriptPayload='{"scriptText":"'"$encoded"'" }'
echo "$scriptPayload"

Try above piece of code. The reason your variable was not evaluating is because you encapsulated it inside single quotes. I happen to close single quote just before variable. That way shell would recognise a variable and replace it with actual contents.


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