How to use sed to replace multiline string? - sed

Question

How can I use the bash sed command to change this string:
<Directory /var/www/>
Options Indexes FollowSymLinks
AllowOverride None
Require all granted
</Directory>
into the following string? (only changing the 3rd line of string)
<Directory /var/www/>
Options Indexes FollowSymLinks
AllowOverride All
Require all granted
</Directory>
NOTE 1: I don't just want to target the string 'AllowOverride None' because there are other occurrences in the file that should not be changed. I need to target the entire string starting with <Directory /var/www>
NOTE 2: I also need to overwrite the file. So, take that into account in your answer. And provide different versions for GNU/non-GNU versions of sed just in case.

Answer 1

Since the patterns contain slashes, use \% (for any character %) to mark the search patterns. Then use:
sed -e '\%^<Directory /var/www/>%,\%^</Directory>% s/AllowOverride None/AllowOverride All/'
The search patterns inside \%…% limit the search to lines between the matching patterns, and the { s/…/…/; } looks for the desired pattern within the range and makes the appropriate replacement.
If you don't want to restrict it to a single directory section but to all directory sections, adjust the start pattern appropriately. For example, this will match any <Directory> section:
sed -e '\%^<Directory [^>]*>%,\%^</Directory>% s/AllowOverride None/AllowOverride All/'
You can make it more selective depending on your requirements.

Answer 2

The simple version, relying on the AllowOverride line coming within two lines after <Directory...> and using a GNU sed extension, is this:
sed '/^<Directory/,+2 { s/AllowOverride None/AllowOverride All/g; }'
UPDATE: Here is the version not relying on any GNU extension (I tried it first, but made a typo and was surprised that it didn't work, that's why a posted the other version first):
sed '/^<Directory/,/^<\/Directory>/ { s/AllowOverride None/AllowOverride All/; }'

Answer 3

I realize this is not what you asked by maybe its worth not using sed?
How about a python solution? It walks directory passed as first parameter to script and replaces exactly <Directory element as you wrote it while only changing None to All and writes changes back to the file. It will also work with different indentation levels while preserving original indentation. Works on both python2 and python3.
After all i am assuming if you have sed you probably have python too.
#!/usr/bin/env python
import re
r = re.compile(r'(<Directory /var/www/>\s+Options Indexes FollowSymLinks\s+AllowOverride )None(\s+Require all granted\s+</Directory>)', re.MULTILINE)
for root, dirs, files in os.walk(sys.argv[1]):
for file_name in files:
if file_name.endswith('.conf'):
file_path = os.path.join(root, file_name)
with open(file_path) as fp:
data = r.sub(r'\1All\2', fp.read())
with open(file_path, 'w+') as fp:
fp.write(data)

Answer 4

Using Gnu Sed:
sed -zie 's!\(<Directory /var/www/>[^<]*AllowOverride\) None!\1 All!' ex1.txt
Option -z is for Null separated records: all the file is one record,
so just make a simple substitution.
[^<]* (multiline) regular expression respects Directory boundaries, and allows flexible format and order.

Answer 5

Your question is a good illustration of the mantra, don't use sed. Really, you shouldn't use any regex engine for context-free language like XML. But you can get close, maybe close enough, with awk.
#! /usr/bin/awk -f
/<Directory \/var\/www\/>/ {
line = NR
}
/ AllowOverride None/ && line + 2 == NR {
gsub( /None/, "All" )
}
{ print }
That way you don't have any fancy, nonstandard regex to read, and your code says exactly what it means: If you find "AllowOverride" 2 lines after the "Directory" line, replace it. The above regexes are both very simple (and Posix compliant) and should work with any version of awk.

Answer 6

Your answer is already given by this user just check here.
Some Reference
In the simplest calling of sed, it has one line of text in the pattern space, ie. 1 line of \n delimited text from the input. The single line in the pattern space has no \n... That's why your regex is not finding anything.
You can read multiple lines into the pattern-space and manipulate things surprisingly well, but with a more than normal effort.. Sed has a set of commands which allow this type of thing... Here is a link to a Command Summary for sed. It is the best one I've found, and got me rolling.
However forget the "one-liner" idea once you start using sed's micro-commands. It is useful to lay it out like a structured program until you get the feel of it... It is surprisingly simple, and equally unusual. You could think of it as the "assembler language" of text editing.
Summary: Use sed for simple things, and maybe a bit more, but in general, when it gets beyond working with a single line, most people prefer something else...
I'll let someone else suggest something else.. I'm really not sure what the best choice would be (I'd use sed, but that's because I don't know perl well enough.)
sed '/^a test$/{
$!{ N # append the next line when not on the last line
s/^a test\nPlease do not$/not a test\nBe/
# now test for a successful substitution, otherwise
#+ unpaired "a test" lines would be mis-handled
t sub-yes # branch_on_substitute (goto label :sub-yes)
:sub-not # a label (not essential; here to self document)
# if no substituion, print only the first line
P # pattern_first_line_print
D # pattern_ltrunc(line+nl)_top/cycle
:sub-yes # a label (the goto target of the 't' branch)
# fall through to final auto-pattern_print (2 lines)
}
}' alpha.txt
Here it is the same script, condensed into what is obviously harder to read and work with, but some would dubiously call a one-liner
sed '/^a test$/{$!{N;s/^a test\nPlease do not$/not a test\nBe/;ty;P;D;:y}}' alpha.txt
Here is my command "cheat-sheet"
: # label
= # line_number
a # append_text_to_stdout_after_flush
b # branch_unconditional
c # range_change
d # pattern_delete_top/cycle
D # pattern_ltrunc(line+nl)_top/cycle
g # pattern=hold
G # pattern+=nl+hold
h # hold=pattern
H # hold+=nl+pattern
i # insert_text_to_stdout_now
l # pattern_list
n # pattern_flush=nextline_continue
N # pattern+=nl+nextline
p # pattern_print
P # pattern_first_line_print
q # flush_quit
r # append_file_to_stdout_after_flush
s # substitute
t # branch_on_substitute
w # append_pattern_to_file_now
x # swap_pattern_and_hold
y # transform_chars