Insert text between two marker lines in bash

Question

I have some lines stored in a text file called bashrc_snippet. I would like to insert them into .bashrc. Since I sometimes change the contents of the text file I would like to be able to re-insert them in the .bashrc-file. To do this I want to use marker lines:

# User things
HISTSIZE=1000

#START
alias ls='ls --color=tty'
... some more lines
#END

I would like a bash script to do this (possibly by using sed or awk). The algoritm should be:

• If the marker lines are missing add them at the end of the file (and the lines of text)
• If the marker lines are present, replace the contents between them with the new lines of text

Answer 1

Hello! I would like to suggest this (ex or vim commands):

ex -c '/^#START/+1,/^#END/-1 d' -c '/^#START/ r bashrc_snippet' -c 'wq'

Answer 2

don't really understand your requirement, but here's a guess

#!/bin/bash

rcfile="$1"
snippet="$2"
var=$(<"$snippet")
if grep -q "START" "$rcfile" ;then
   awk -v v="$var" '/START/ {
     print $0
     print v
     f=1
   }f &&!/END/{next}/END/{f=0}!f' "$rcfile" >t && mv t "$rcfile"
else
   echo "#START" >> "$rcfile"
   echo "$var" >> "$rcfile"
   echo "#END" >> "$rcfile"
fi

to use:

$  ./test.sh rc_file bashrc_snippet