Mdtryhht

On queue-based clusters the Queue of pending jobs is shown from a command, say showqueue.

The command returns, in columns, a list of reasonable data like names, etc, but the columns/data don't really matter for the question.

I like using the utility watch like watch showqueue at times (with an alias of alias watch="watch " to force alias expansion of my command to watch). There is valuable data (Running jobs), in the first few lines, then pending jobs, etc, and some valuable summaries at the end.

However, at times the output of showqueue goes off the screen (Unbelievable, I know)! Ideally, I'd like some way to be able to see the beginning and end of the file at the same time.

The best I have so far is: showqueue > file; head -n 20 file > file2; echo "..." >> file2 ; tail -n 20 file >> file2; cat file2, and using watch on an alias of that.

Does anyone know of anything a little more flexible or single-utility? My solution gets a little nastier with bash loops to make the "..." break multilined, it's not adaptive to resizing the terminal window at all, and I'm sure there's more that I missed.

Any suggestions?

Are you looking to do something like the following? Shows output from both head and tail.

$ showqueue | (head && tail)

awk solution for an arbitrary number of lines shown from the head and the tail (change n=3 to set the amount):

$ seq 99999 | awk -v n=3 'NR <= n; NR > n a[NR] = $0; delete a[NR-n]; 
 END print "..."; for (i = NR-n+1; i <= NR; i++) if (i in a) print a[i]; '
1
2
3
...
99997
99998
99999

As it's written, the head and tail parts will not overlap, even if the input is shorter than 2*n lines.

_{In some awk implementations, using for (x in a) print a[x]; in the END part also works. But in general, it's not guaranteed to return the array entries in the correct order, and doesn't in e.g. mawk.}

You can use simple awk script. Added circle buffer there n=3 is for last 3 lines

awk 'NR<=n print $0 A[NR%n]=$0 END for (i=1; i<=n; ++i) print A[(NR+i)%n] ' n=3 < <( showqueue )

Using the same approach as you, using a temporary file, but doing it slightly shorter:

showqueue >/tmp/q.out; head -n 20 /tmp/q.out; echo '...'; tail -n 20 /tmp/q.out

This would not suffer from the same issues as discussed under another answer, but would possibly show the same lines twice if the output was shorter than 40 lines.