Shell – bash / sh script to replace text between some tags/strings in a text file

openwrtreplaceshell

I am creating executable which will be executed with /bin/sh or /bin/bash script,
I have a file which contains a structure like, there will be only one #start and #end tag in the config file, and I want to replace text in between those tags,

...

#start
FirewallRuleSet global {
    FirewallRule allow tcp to google.com
    FirewallRule allow tcp to facebook.com

#more rules
}
#end

FirewallRuleSet known-users {
    FirewallRule allow to 0.0.0.0/0
}

...

Desired output will be, 

...

#start
FirewallRuleSet global {
    FirewallRule allow tcp to google.com
    FirewallRule deny tcp to facebook.com
    FirewallRule deny tcp to twitter.com
    FirewallRule allow tcp to exaple.com



#more rules
}
#end

FirewallRuleSet known-users {
    FirewallRule allow to 0.0.0.0/0
}

...

How can I replace the whole text between #start and #end with some new text? I just want to add or remove Rules from this config file.

This is part of a config file and I want to modify url allowed inside that texts.

Best Answer

Use

sed '/#start/,/#end/replace_command'

For example, if the file is called myconfig, and you want to replace "allow" with "deny" in that section, you could say

sed '/#start/,/#end/s/allow/deny/' myconfig

That would leave the file untouched, and display on the standard output what the file would look like after the modification.  You should probably do that first, to verify that you've got the command right.  If you want to actually change the file, add the -i option:

sed -i '/#start/,/#end/s/allow/deny/' myconfig

If you want to replace the whole text (all the text) between those two lines, you can do something slightly simpler than Lucas's answer:

sed '/#start/,/#end/c\
New text line 1\
New text line 2\
        ︙      \
New text line n-1\
New text line n (last)'                                   ← Close quote; no backslash here

c is the change command in sed (and ed); it means "replace entire line(s)".  You cannot simply leave the #start and #end lines untouched.  If you want to keep them, you must re-insert them:

sed -i '/#start/,/#end/c\
#start\
FirewallRuleSet global {\
    FirewallRule allow tcp to google.com\
    FirewallRule deny tcp to facebook.com\
                      ︙                 \
\
#more rules\
}\
#end' myconfig

/#start/,/#end/ specifies a range — the lines from the first line that contains #start through the first line after that that contains #end.  If you need to find lines that contain those strings and nothing else, use /^#start$/,/^#end$/.

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