Code example demonstrating the use of sed with shell to replace special characters in variables

Utilize a corresponding tool that directly interprets the substitution variable without alteration. The (ref) tool possesses this capability because variables, if included in the environment through exporting or setting them in the invocation line, are treated as first class entities. Only four specific characters within the substitution part of the sed command need to be escaped, as mentioned in this reference, despite the question being criticized for its general nature within the SE community. These special characters include a comma, a newline, and the delimiter (typically denoted as ‘but can actually be any character’).

Solution 1:

To separate commands, any character, such as


, can be used as a delimiter. For instance,

sed -i -e "s|$answer|$FORME $answer|g" ~$answer.txt

Solution 2:

Surprisingly, this question is frequently asked and addressed on various Stack Exchange platforms. However, the two valuable responses to this logical query are difficult to find amidst a vast amount of information. These responses can be likened to needles hidden within a haystack.

1. Only escape four specific special characters within your variable.

The question mentioned here, although it is a general question that is not favored by SE, highlights the four characters that are considered special in the replacement part of the sed command:





, as well as newline and the delimiter (typically


, but it can be any character).

To utilize an arbitrary variable as a substitute in sed, ensure to escape any instances of those four characters beforehand.

REPL='Arbitrary variable potentially with special characters like / and & and  and 
REPL=$(sed -e 's/[&\/]/\&/g; s/$/\/' -e '$s/\$//' <<<"$REPL")
hexdump -C <<< "$REPL"

For example:

REPL=$(sed -e 's/[&\/]/\&/g; s/$/\/' -e '$s/\$//' <<<"$REPL")
sed "s/x/$REPL/" <<< "STARTxEND"



as expected.

2. Employ a comparable tool that directly interprets the replacement variable.

Variables in (ref) have the ability to be treated as first-class citizens, as long as they are included in the environment through exporting or setting them in the invocation line. It is worth noting that the use of


is not necessary in the replacement string, but it can be helpful in the regular expression string.

export REPL='/& 
perl -pe 's/x/$ENV{REPL}/' <<< "STARTxEND"



The mentioned code,


, does not work, even with a reference.

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