I wish to write a shell script whereby I could read the file from command and edit the file without manual intervention (based on searching some text and replacing it with another).
I need not use any text editor for this....simply text-searching (like using grep) and then replacing it with some other text and saving the changes....
That is where sed comes in to play. A sed command has this format:
[pattern1][,pattern2][!] command [args]
It uses regexes so it can/will be a bit difficult. Some basic examples taken from the 2nd link below:
# substitute (find and replace) "foo" with "bar" on each line
sed 's/foo/bar/' # replaces only 1st instance in a line
sed 's/foo/bar/4' # replaces only 4th instance in a line
sed 's/foo/bar/g' # replaces ALL instances in a line
sed 's/(.*)foo(.*foo)/1bar2/' # replace the next-to-last case
sed 's/(.*)foo/1bar/' # replace only the last case
# substitute "foo" with "bar" ONLY for lines which contain "baz"
sed '/baz/s/foo/bar/g'
# substitute "foo" with "bar" EXCEPT for lines which contain "baz"
sed '/baz/!s/foo/bar/g'
# change "scarlet" or "ruby" or "puce" to "red"
sed 's/scarlet/red/g;s/ruby/red/g;s/puce/red/g' # most seds
gsed 's/scarlet|ruby|puce/red/g' # GNU sed only
Some references
