processing lines in a file

[boondocks]

I am able to add text to the beginning of a line with:

sed 's/^/ LINE_start /g' inputfile.txt > outputfile.txt
I am able to add text to the end of a line with:

sed 's/$/ LINE_stop /g' inputfile.txt > outputfile.txt
But how do I add text to the beginning and end of a line, only if it contains a pattern.
So if the line contains "some food" like:
There is some food in the kitchen.
Then update the line with:
! Eureka ->> There is some food in the kitchen. <<- Found it !

And if the line does not contain "some food" then ignore it.

[Portmanteaufu]

I think backreferences will help you out here, though there may be a more elegant way of doing things.



cat myfile.txt | sed 's/^\(.*\)\(some food\)\(.*\)$/!!! Eureka-> \1\2\3 <- Found it!/


In the second part of a sed command, \1 refers to "whatever was found in the first set of \(\) parenthases", \2 the second set of parens, etc. This method ensures that "some food" appears someplace in the middle of the line and then reconstructs the line with the necessary additions.

[Portmanteaufu]

As an alternative, if you're just trying to view the contents of a file with the important bits highlighted, you can always do this:



grep --color=auto 'pattern|$' file_to_display


This will print any line that either:
1.) Contains the pattern you specify
or
2.) Has an end. (That is to say, all of them because every line has an end.)

The result is that all of the lines of the file you specify are dumped to the terminal, but all of the words matching your pattern (e.g. "some food") are in bright red. (The color is configurable via environment variable.)

[boondocks]

I think backreferences will help you out here, though there may be a more elegant way of doing things.



cat myfile.txt | sed 's/^\(.*\)\(some food\)\(.*\)$/!!! Eureka-> \1\2\3 <- Found it!/


In the second part of a sed command, \1 refers to "whatever was found in the first set of \(\) parenthases", \2 the second set of parens, etc. This method ensures that "some food" appears someplace in the middle of the line and then reconstructs the line with the necessary additions.
Portmanteaufu,
Thank you, once again!