从文件中删除所有行，以特定字符串开头和结尾

Question

I need to check if a file contains a specific two strings and if it does, remove all the text between them (strings included). Let's say I have a file text which looks something like this:

line of text
line of text
line of text
line of text
#1st string
line of text
line of text
line of text
#2nd string

Now I would like to delete all the lines between #1st string and #2nd string and those two strings included.

I tried getting the whole text into a variable and then removing them like that:

prefix="#1st string"
suffix="#2nd string"

#content of a file into variable
tempfile=$( cat text )
tempfile=${tempfile#"$prefix"}
tempfile=${tempfile%"$suffix"}
echo ${tempfile}

Unfortunately, this doesn't work because the text file contains some commands which somehow list the content of the current directory and blend the output into the variable which leaves the file corrupted. Can I prevent that somehow, or is there a better way of achieving this altogether?

Answer 1

You could use sed to remove the line range:

sed '/#1st string/,/#2nd string/d' text

To store the result in-place, use

sed -i '/#1st string/,/#2nd string/d' text

or the more portable

sed '/#1st string/,/#2nd string/d' text > tempfile && mv tempfile text

And finally, because you might have files where only the first string exists, you have to check existence of the second string first:

grep -q '#2nd string' text && sed '/#1st string/,/#2nd string/d' text

Answer 2

You could use grep's before and after feature:

prefix="#1st string"
suffix="#2nd string"

grep -B 100000000 $prefix text | grep -v $prefix > output
grep -A 100000000 $suffix text | grep -v $suffix >> output