What delimiters can you use in sed?

Question

I am using sed in a shell script to edit filesystem path names. Suppose I want to replace

/foo/bar

with

/baz/qux

However, sed's s/// command uses the forward slash / as the delimiter. If I do that, I see an error message emitted, like:

▶ sed 's//foo/bar//baz/qux//' FILE
sed: 1: "s//foo/bar//baz/qux//": bad flag in substitute command: 'b'

Similarly, sometimes I want to select line ranges, such as the lines between a pattern foo/bar and baz/qux. Again, I can't do this:

▶ sed '/foo/bar/,/baz/qux/d' FILE
sed: 1: "/foo/bar/,/baz/qux/d": undefined label 'ar/,/baz/qux/d'

What can I do?

Answer 1

You can use an alternative regex delimiter as a search pattern by backslashing it:

sed '\,some/path,d'

And just use it as is for the s command:

sed 's,some/path,other/path,'

You probably want to protect other metacharacters, though; this is a good place to use Perl and quotemeta, or equivalents in other scripting languages.

From man sed:

/regexp/
Match lines matching the regular expression regexp.

\cregexpc
Match lines matching the regular expression regexp. The c may be any character other than backslash or newline.

s/regular expression/replacement/flags
Substitute the replacement string for the first instance of the regular expression in the pattern space. Any character other than backslash or newline can be used instead of a slash to delimit the RE and the replacement. Within the RE and the replacement, the RE delimiter itself can be used as a literal character if it is preceded by a backslash.

Answer 2

Perhaps the closest to a standard, the 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."