Shell Programming and Scripting

Hey, I am working on some file comparisons with csv files. csv files use "," as the field separator and I want to do a

Code:

cat -n file > file

to put the file numbers at the beginning of the lines, but cat uses "\t" as the separator. Can I force cat to use "," as the Output file separator. Or can i use

Code:

awk '{print getline}{print ","}{print $0}' file > file

Same file for input and output won't work (some cat's actually complain if input and output files are the same):

Code:

$ cat -n FILE > FILE
cat: FILE: input file is output file

If you need to update file in-place try somehting like this

Code:

cat -n file | sed 's/\t/,/' > file2; mv file2 file

cat doesn't care about the value of $OFS, as it just takes one file and prints it as-is on stdout.

But you can get a similar effect using perl -i.bak -ne 'printf "%d,%s", $., $_' file

@pludi thanks for your excellent reply. That code worked great. Could you please explain how it works, in particular the

Code:

-i.bak -ne 'printf "%d,%s", $., $_'

part.

@Chubler_XL, I know cat dosn't like the same output and input stuff, my code on that line is actually a fairly long pipe getting input and then outputting it to a temp file. But thanks for the reply.

---------- Post updated at 12:30 AM ---------- Previous update was at 12:12 AM ----------

nevermind, I found a bash only alternative
here. (can't post urls until 5 posts!)

Code:

awk '{printf "%s,%s\n",NR,$0}' FILE

That last one isn't bash only, it's using awk instead of Perl.

Explanation of my code:

Code:

awk '$0=NR","$0' infile

could you please explain the code..especially this part

Code:

'$0=NR