POSIX/IEEE Open Group Base Specification says:
Substitute the replacement string for instances of the BRE in the pattern space. Any character other than backslash or newline can be used instead of a slash to delimit the BRE and the replacement. Within the BRE and the replacement, the BRE delimiter itself can be used as a literal character if it is preceded by a backslash.
There are cases when the delimiter
sed replacement is in the BRE or replacement, triggering errors like:
$ echo "2/3/4" | sed "s/2/3/X/" sed: -e expression #1, char 7: unknown option to `s'
For this, we can use different delimiters such as
_ or even a space:
$ echo "2/3/4" | sed "s#2/3#X#" X/4 $ echo "2/3/4" | sed "s_2/3_X_" X/4 $ echo "2/3/4" | sed "s 2/3 X " X/4