Way to print last line of a file then first line of a file in awk only

awk

I have searched, but have come up short with an answer. I want to print the last line (or record) in a file; then print the first line using only awk. I know how to print first line:

NR == 1{print}

and last line

END{print}

However, how can I switch the positions? Is it even possible? I only get errors when I try to do so. Is there a way to integrate the

NR == 1{print}

command into the END command?
Again, I only want to perform this in awk. Thanks!

Best Answer

Just save the first line to a variable

awk 'NR==1 {first = $0} END {print; print first}' file

Ex. given file as

line 1
line 2
line 3
line 4
line 5

then

$ awk 'NR==1 {first = $0} END {print; print first}' file
line 5
line 1

Related Solutions

AWK – Process Last Line First Using AWK

You can do it as a two-pass solution in awk:

awk 'FNR == NR { n = $2; next } { print $1, $2/n }' infile infile

If your version of awk supports the ENDFILE block (e.g. GNU awk 4+), you can do it like this:

awk 'ENDFILE { n = $2 } FNR != NR { print $1, $2/n }' infile infile

Note that it is more efficient to seek to the end of the file first see camh's answer.

Explanation

The first example works by remembering the previous $2, i.e. it is only evaluated when the local line counter (FNR) is equal to the global line counter (NR). The next command skips to the next line, in this case it ensures that the last block is only evaluated when the second argument is parsed.

The second example has similar logic, but takes advantage of the the ENDFILE block which is evaluated when the end of an input-file is reached.

Shell – Print first and last line of all files in folder

So I like sed the answer can be

for file in file.log.*
do
   echo "file: $file"
   echo -n "first line: "
   cat "$file" | sed -n '/^\s*$/!{p;q}'
   echo -n "last line: "
   tac "$file" | sed -n '/^\s*$/!{p;q}'
done

Best Answer

Related Solutions

AWK – Process Last Line First Using AWK

Shell – Print first and last line of all files in folder

Related Question