Table of Contents

replace text between two lines with a file

tags | line numbers, sed command to insert a file

Replace lines between \$start and \$end in main.txt with contents of part.txt 

sed -e "$start e cat part.txt" -e "$start,$end d" main.txt

Sample command: 

sed -e "1 e cat part.txt" -e "1,2 d" main.txt
$ cat main.txt
a b c
d e f
g h i
j k l

$ cat part.txt
x y z
p q r
s t u

$ start=1; end=2; sed -e "$start e cat part.txt" -e "$start,$end d" main.txt
x y z
p q r
s t u
g h i
j k l

$ start=2; end=4; sed -e "$start e cat part.txt" -e "$start,$end d" main.txt
a b c
x y z
p q r
s t u

$ start=2; end=3; sed -e "$start e cat part.txt" -e "$start,$end d" main.txt
a b c
x y z
p q r
s t u
j k l

$ start=2; end=2; sed -e "$start e cat part.txt" -e "$start,$end d" main.txt
a b c
x y z
p q r
s t u
g h i
j k l

insert file at the beginning of another file

This will insert part.txt at the beginning of main.txt. 

sed -e "1 e cat part.txt" main.txt

Example: 

$ cat main.txt
a b c
d e f
g h i
j k l

$ cat part.txt
x y z
p q r
s t u

$ sed -e "1 e cat part.txt" main.txt
x y z
p q r
s t u
a b c
d e f
g h i
j k l

Found it in: https://unix.stackexchange.com/questions/337435/sed-insert-file-at-top-of-another

backup with timestamp

tags | sed create backup, YYYYMMDD_HHMMSS 

sed "-i_asof_`date +%Y%m%d_%H%M%S`" -e 's/foo/bar/g' main.txt

will backup to something like main.txt_asof_20210128_151656 

sed "-i.`date +%F`" -e 's/foo/bar/g' main.txt

will backup to something like main.txt.2021-01-28

sed do not change line endings

sed -b

Ref:- https://stackoverflow.com/questions/4652652/preserve-line-endings

replace double quote with single quote

sed "s/\"/'/g"

Ref:- https://stackoverflow.com/questions/16154007/replace-all-double-quotes-with-single-quotes

Sample run: 

% sed "s/\"/'/g"
a
a
"
'
'
'