Modify awk script to add looping logic - unix

Question

I have an awk script to print pids appearing in myfilename. Where myfilename contains a list of pids each one appearing on a new line...
ps -eaf | awk -f script.awk myfilename -
And here is the contents of script.awk...
# process the first file on the command line (aka myfilename)
# this is the list of pids
ARGIND == 1 {
pids[$0] = 1
}
# second and subsequent files ("-"/stdin in the example)
ARGIND > 1 {
# is column 2 of the ps -eaf output [i.e.] the pid in the list of desired
# pids? -- if so, print the entire line
if ($2 in pids)
printf("%s\n",$0)
}
At the moment the comman prints out pids in order of the ps -eaf command however I would like it to print out pids as per the order that they appear in myfilename.
I tried to modify the script to loop through $pids and repeat the same logic but I couldn't quite get it right.
Appreciate it if someone could help me with this.
thanks

Answer 1

Forgive my rusty AWK. Perhaps this is usable?
ARGIND == 1 {
pids[$0] = NR # capture the order
}
ARGIND > 1 {
if ($2 in pids) {
idx = pids[$2];
matches[idx] = $0; # capture the line and associate it with the ps -eaf order
if (idx > max)
max = idx;
}
}
END {
for(i = 1; i <= max; i++)
if (i in matches)
print matches[i];
}
I don't know what the output from ps -eaf looks like or what assumptions might be useful to exploit from its output. When I first read the question I thought OP had more than two inputs to the script. If it's really going to be only two then it probably makes more sense to reverse the inputs, if not then this might be the more general approach.

Answer 2

I would instead do this using the time-honoured NR==FNR construct. It goes a little something like this (one-liner).
ps -eaf | awk 'NR==FNR{p[$1]++;next} $2 in p' mypidlist -
The idea of NR==FNR is we look at the current record number (NR), and compare it to the record number within the current file (FNR). If they are the same, we are in the same file, so we store a record and move to the next line of input.
If NR==FNR is not true, then we simply check for $2 being in the array.
So the first expression populates the array p[] with the contents of mypidlist, and the second construct is a condition only, which defaults to {print} as its statement.
Of course, the one-liner above does not address your requirement to print results in the order of your pid input file. To do that, you need to keep an index and record the data in an array for some kind of sort. Of course, it doesn't have to be a real sort, just keeping the index itself should be sufficient. The following is a bit long as a one-liner:
ps -eaf | awk 'NR==FNR{p[$1]++;o[++n]=$1;next} $2 in p {c[$2]=$0} END {for(n=1;n<=length(o);n++){print n,o[n],c[o[n]]}}' mypidlist -
Broken out for easier reading, the awk script looks like this:
# Record the pid list...
NR==FNR {
p[$1]++ # Each pid is an element in this array.
o[++n]=$1 # This array records the order of the pids.
next
}
# If the second+ input source has a matching pid...
$2 in p {
c[$2]=$0 # record the line in a third array, pid as key.
}
END {
# At the end of our input, step through the ordered pid list...
for (n=1;n<=length(o);n++) {
print c[o[n]] # and print the collected line, using our pid index as key.
}
}
Note that in the event a pid from your list is missing from ps output, the result will be to print a blank line, since awk doesn't complain about references to nonexistent array indices.
Note also that length(arrayname) notation works in GAWK and OneTrueAwk, but may not be universal. If that doesn't work for you, you might be able to add an something like this to your awk script:
function alength(arrayname, i, n) {
for(i in arrayname)
n++
return n
}

Answer 3

If there is one file, you can flip the order of inputs and use idiomatic awk as follows
$ awk 'NR==1; NR==FNR{a[$2]=$0;next} $0 in a{print a[$0]}' <(ps -eaf) <(seq 10)
UID PID PPID C STIME TTY TIME CMD
root 1 0 0 02:36 ? 00:00:03 /sbin/init
root 2 0 0 02:36 ? 00:00:00 [kthreadd]
root 3 2 0 02:36 ? 00:00:00 [ksoftirqd/0]
root 4 2 0 02:36 ? 00:00:00 [kworker/0:0]
root 5 2 0 02:36 ? 00:00:00 [kworker/0:0H]
root 6 2 0 02:36 ? 00:00:00 [kworker/u30:0]
root 7 2 0 02:36 ? 00:00:00 [rcu_sched]
root 8 2 0 02:36 ? 00:00:00 [rcuos/0]
root 9 2 0 02:36 ? 00:00:00 [rcuos/1]
root 10 2 0 02:36 ? 00:00:00 [rcuos/2]
Here, the list of the ids provided by the seq, substitute with your file.