Ytdyklly

So I am loading in a properties file to define some variables. In this example imagine it is a string mark!slashending called INPUT.

INPUT is declared by loading in the properties file using:

. ./properties

where

INPUT=mark!slashending

I need the final output to be a script run through SED of the form s!@output@!$INPUT!g such that when executed, @output@ is replaced in another file with the input from the properties file defined by the user (the variable, in this case, is INPUT). We are using ! as the delimiter in SED so this character will need to be escaped (as well as any ) before added to the SED template file.

If I try

echo SAFE_INPUT=$(printf '%sn' 'mark!slashending' | sed 's:[!]:\&:g')

I get the expected output

mark!slash\ending\

If, however, I try

SAFE_INPUT=$(printf '%sn' "${INPUT}" | sed 's:[!]:\&:g')

I get

mark!slashending

I am assuming it is something to do with my declaration of string vs a variable but I am at a loss as to the difference and how to solve the issue right now.

Edit:
On further testing INPUT as read using

. ./properties

is printed as

mark!slashending

So this is not an issue with SED but with reading in the property file.

The problem is when you set variable INPUT in file properties like shown in the question

INPUT=mark!slashending

and source it as a shell script.

The first e is replaced by the shell with e and the at the end of the line will either be removed if there is some whitespace following it, otherwise it denotes that the line is continied in the next line. So the value of INPUT will already be modified.

You either have to define your input with quotes

INPUT='mark!slashending'

like in Cornholio's answer or you have to parse your properties file in a different way.

With the following command you will get variable INPUT (and others if there are more lines in properties) set to the correct value.

eval $(sed -e 's:[!]:\&:g' properties)

This will let the shell evaluate the output of the sed command which replaces and ! and in the contents of properties. The result will be variables with the original names INPUT etc. This will work if your properties file contains one or more variable assignments. It may give strange result with other shell script code.

Note: If your input file contains other special characters, the peprocessing would be more difficult. So using eval this way without additional checking may be fragile or dangerous.

With your example the variable INPUT will have the intended value mark!slashending

After this you can do

SAFE_INPUT=$(printf '%sn' "${INPUT}" | sed 's:[!]:\&:g')

if you need variable SAVE_INPUT to contain mark!slash\ending\.

A better way would be to read the input line by line with while read -r line and check and process the line to separate variable name and value.

If I do the following, with the value of INPUT quoted, it works:

> INPUT='mark!slashending'

> SAFE_INPUT=$(printf '%sn' "${INPUT}" | sed 's:[!]:\&:g')

> echo $SAFE_INPUT

mark!slash\ending\

Note, it's an exact copy of your script, with INPUT= added by me.