How to add a header and/or footer to a sed or awk stream?

Question

I have a bunch of output going through sed and awk.

How can I prefix the output with START and suffix the answer with END?

For example, if I have

All this code
on all these lines
and all these

How could I get:

START
All this code
on all these lines
and all these
END

?

My attempt was:

awk '{print "START";print;print "END"}'

but I got

...
START
    All this code
END
START
    on all these lines
END
START
    and all these
END

Solution 1

This works, as indicated by jasonwryan:

awk 'BEGIN{print "START"}; {print}; END{print "END"}'

Solution 2

This can be done in sed with

sed -e $'1i\\\nSTART' -e $'$a\\\nEND'

1i means insert before line 1; $a means append after the last line.  The $'…' syntax is bash-specific.  In other shells, you should be able to do this with:

sed -e '1i\Enter
START' -e '$a\Enter
END'Enter

Warning: the question says “I have a bunch of output ...”  If you run the above command with no data, you will get no output, because the command depends on there actually being a first line and a last line.  The other two answers will give the header and footer even if the input is null.

Solution 3

If you're already using sed, you can use 1 to match the first line and $ to match the last line (see Scott's answer). If you're already using awk, you can use a BEGIN block to run code before the first line and an END block to run code after the last line (see Michael Durrant's answer).

If all you need to do is add a header and a footer, just use echo and cat.

echo START
cat
echo END

In a pipeline, to run multiple commands, use { … } to tell the parser that they're one single compound command.

content-generator |
{ echo START; cat; echo END; } |
postprocessor

Solution 4

sed -e '1s/.*/START\n&/g' -e '$s/.*/&\nEND/g' filename

START
All this code
on all these lines
and all these
END

Python

#!/usr/bin/python
k=open('filename','r')
o=k.readlines()
for i in range(0,len(o),1):
    if ( i == 0 ):
        print "START"
        print o[i].strip()
    elif ( i == (len(o)-1)):
        print o[i].strip()
        print "END"
    else:
        print o[i].strip()

output

START
All this code
on all these lines
and all these
END

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