sed Using different delimiters


POSIX/IEEE Open Group Base Specification says:

[2addr] s/BRE/replacement/flags

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 / for 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 _ or even a space:

$ echo "2/3/4" | sed "s#2/3#X#"
$ echo "2/3/4" | sed "s_2/3_X_"
$ echo "2/3/4" | sed "s 2/3 X "