awk Joining n fields with delimiter - awk

Question

How can I use awk to join various fields, given that I don't know how many of them I have? For example, given the input string
aaa/bbb/ccc/ddd/eee
I use -F'/' as delimiter, do some manipulation on aaa, bbb, ccc, ddd, eee (altering, removing...) and I want to join it back to print something line
AAA/bbb/ddd/e
Thanks

Answer 1

... given that I don't know how many of them I have?
Ah, but you do know how many you have. Or you will soon, if you keep reading :-)
Before giving you a record to process, awk will set the NF variable to the number of fields in that record, and you can use for loops to process them (comments aren't part of the script, I've just put them there to explain):
$ echo pax/is/a/love/god | awk -F/ '{
gsub (/god/,"dog",$5); # pax,is,a,love,dog
$4 = ""; # pax,is,a,,dog
$6 = $5; # pax,is,a,,dog,dog
$5 = "rabid"; # pax,is,a,,rabid,dog
printf $1; # output "pax"
for (i = 2; i <= NF; i++) { # output ".<field>"
if ($i != "") { # but only for non-blank fields (skip $4)
printf "."$i;
}
}
printf "\n"; # finish line
}'
pax.is.a.rabid.dog
This shows manipulation of the values, as well as insertion and deletion.

Answer 2

The following will show you how to process each field and do some example manipulations on them.
The only caveat of using the output field separator OFS is that "deleted" fields will still have delimiters as shown in the output below; however it makes the code much simpler if you can live with that.
awk '
BEGIN{FS=OFS="/"}
{
for(i=1;i<=NF;i++){
if($i == "aaa")
$i=toupper($i)
else if($i ~ /c/)
$i=""
else if($i ~ /^eee$/)
$i="e"
}
}1' <<<'aaa/bbb/ccc/ddd/eee'
Output
AAA/bbb//ddd/e

Answer 3

This might work for you:
echo "aaa/bbb/ccc/ddd/eee" |
awk 'BEGIN{FS=OFS="/"}{sub(/../,"",$4);NF=4;print}'
aaa/bbb/ccc/d
To delete fields not at the end use a function to shuffle the values:
echo "aaa/bbb/ccc/ddd/eee" |
awk 'func d(n){for(x=n;x<=NF-1;x++){y=x+1;$x=$y}NF--};BEGIN{FS=OFS="/"}{d(2);print}'
aaa/ccc/ddd/eee
Deletes the second field.

Answer 4

awk -F'/' '{ # I'd suggest to add them to an array, like:
# for (i=1;i<=NF;i++) {a[i]=$i }
# Now manipulate your elements in the array
# then finally print them:
n = asorti(a, dest)
for (i=1;i<=n;i++) { output+=dest[i] "/") }
print gensub("/$","","g",output)
}' INPUTFILE
Doing it this way you can delete elements as well. Note deleting an item can be done like delete array[index].