Elegant way to reverse column order

Question

Hi,

I have a file named ip-list with two columns:

IP1  <TAB>  Server1
IP2  <TAB>  Server2

And I want to produce:

Server1  <TAB>  IP1
Server2  <TAB>  IP2

What's the most elegant, shortest Linux command line tool to do it?

Answer 1

The simplest solution is:

awk '{print $2 "\t" $1}'

However, there are some issues. If there may be white space in either of the fields, you need to do one of: (depending on if your awk supports -v)

awk -v FS='\t' '{print $2 "\t" $1}'
awk 'BEGIN{ FS="\t" } {print $2 "\t" $1}'

Alternatively, you can do one of:

awk -v OFS='\t' '{print $2,$1}'
awk 'BEGIN{ OFS="\t" } {print $2,$1}'
awk -v FS='\t' -v OFS='\t' '{print $2,$1}' # if allowing spaces in fields

One of the comments asks, 'where does the filename go'? awk is used as a filter, so it would typically appear as:

$ some-cmd | awk ... | other-cmd

with no filename given. Or, a filename can be given as an argument after all commands:

$ awk ... filename

Answer 2

perl -pi -e 's/^([^\t]+)\t([^\t]+)$/\2\t\1/' yourfile.csv

perl -pi -e 'split("\t"); print "$_[1]\t$_[0]"'

The first one probably works on sed, too.

Answer 3

Use awk:

awk '{print $2,$1}' ip-list

That should give you what you want.

Answer 4

Depends on your environment, but cut is probably the command you are looking for.

$ cat yourfile.csv | cut -f 2,1