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I would like to change the format of the output xargs displays cat k.txt 1 2 3

And

cat k.txt | xargs 
1 2 3

However I would like to have 1, 2, 3 or 1|2|3. Any suggestions?

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That could be achieved with something (not exactly this) like xargs cat -n, but is easier if you just trim the newline characters, this can be achieved with echo $(cat), grep or awk (crawl the way to do it). xargs don't fit well for your current purpose. –  galegosimpatico Sep 2 '13 at 10:13

2 Answers 2

up vote 9 down vote accepted

Below are a dozen or so examples of how you can take a file such as this:

$ cat k.txt
1
2
3

and convert it to this format:

1,2,3

You can use this command to create the above file if you'd like to play along:

$ cat <<EOF > k.txt
1
2
3
EOF

The examples below are split into 2 groups. Ones that "work" and ones that "almost" work. I leave these because often times it's just as valuable to see why something doesn't work, as it is to see why something does.

Most scripting languages that I'm familiar with are represented. Some are represented multiple times, since as with the famous acronym typically referenced in Perl, TIMTOWTDI.

NOTE: You can swap out the comma (,) in the examples below and replace it with whatever characters you want, i.e. |.

Examples that "work"

These code snippets will produce the desired output.

The paste command:

$ paste -s -d ',' k.txt 
1,2,3

The sed command:

$ sed ':a;N;$!ba;s/\n/,/g' k.txt
1,2,3

$ sed ':a;{N;s/\n/,/};ba' k.txt 
1,2,3

The perl command:

$ perl -00 -p -e 's/\n(?!$)/,/g' k.txt
1,2,3

$ perl -00 -p -e 'chomp;tr/\n/,/' k.txt
1,2,3

The awk command:

$ awk '{printf"%s%s",c,$0;c=","}' k.txt
1,2,3

$ awk '{printf "%s,",$0}' k.txt | awk '{sub(/\,$/,"");print}'
1,2,3

$ awk -vORS=, 1 k.txt | awk '{sub(/\,$/,"");print}'
1,2,3

$ awk 'BEGIN {RS="dn"}{gsub("\n",",");print $0}' k.txt | awk '{sub(/\,$/,"");print}'
1,2,3

The python command:

$ python -c "import sys; print sys.stdin.read().replace('\n', ',')[0:-1]" <k.txt
1,2,3

$ python -c "import sys; print sys.stdin.read().replace('\n', ',').rstrip(',')" <k.txt
1,2,3

Bash's mapfile built-in:

$ mapfile -t a < k.txt; (IFS=','; echo "${a[*]}")
1,2,3

The ruby command:

$ ruby -00 -pe 'gsub /\n/,",";chop' < k.txt
1,2,3

$ ruby -00 -pe '$_.chomp!"\n";$_.tr!"\n",","' k.txt
1,2,3

The php command:

$ php -r 'echo strtr(chop(file_get_contents($argv[1])),"\n",",");' k.txt
1,2,3

Caveats

Most of the examples above will work just fine. Some have hidden issues, such as the PHP example above. The function chop() is actually an alias to rtrim(), so the last line's trailing spaces will also be removed.

So too do does the first Ruby example, and the first Python example. The issue is with how they're all making use of a type of operation that essentially "chops" off, blindly, a trailing character. This is fine in for the example that the OP provided, but care must be taken when using these types of one liners to make sure that they conform with the data they're processing.

Example

Say our sample file, k.txt looked like this instead:

$ echo -en "1\n2\n3" > k.txt

It looks similar but it has one slight difference. It doesn't have a trailing newline (\n) like the original file. Now when we run the first Python example we get this:

$ python -c "import sys; print sys.stdin.read().replace('\n', ',')[0:-1]" <k.txt
1,2,

Examples that "almost" work

These are the "always a bridesmaid, never a bride" examples. Most of them could probably be adapted, but when working a potential solution to a problem, when it feels "forced", it's probably the wrong tool for the job!

The perl command:

$ perl -p -e 's/\n/,/' k.txt
1,2,3,

The tr command:

$ tr '\n' ','  < k.txt 
1,2,3,

The cat + echo commands:

$ echo $(cat k.txt)
1 2 3

The ruby command:

$ ruby -pe '$_["\n"]=","' k.txt
1,2,3,

Bash's while + read built-ins:

$ while read line; do echo -n "$line,"; done < k.txt
1,2,3,
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1  
Why no ruby? ruby -pe '$_["\n"]=","' k.txt –  manatwork Sep 2 '13 at 12:38
    
Regarding awk I prefer a shorter alternative: awk -vORS=, 1 k.txt –  manatwork Sep 2 '13 at 12:39
    
Not sure whether CentOS has bash: mapfile -t a < k.txt; (IFS=','; echo "${a[*]}") –  manatwork Sep 2 '13 at 12:42
    
not sure about the trailing newline. According to my test your perl and first awk has them too. –  manatwork Sep 2 '13 at 12:44
    
I would put the paste one at the top. That's exactly what paste -s is for here. It's a standard command and would be the most efficient. All the other ones are overkill and/or are not portable or have limitations. –  Stéphane Chazelas Sep 2 '13 at 12:46

@slm already given nice answer, but as your question "format output of xargs"

xargs -I{} echo -n "{}|" < test.txt
  • -I is "replace strings" option.
  • {} is a placeholder for output text.
  • This is similar to the use of a curly-bracket pair in "find."

If you want to get rid of the trailing | you can use sed to do some clean up:

$ xargs -I{} echo -n "{}|" < k.txt  | sed -e 's/|$//'
1|2|3
share|improve this answer
    
That tacks an extra pipe on after the 3. "1|2|3|". I've been having the same issue with a while loop and awk solution. –  slm Sep 2 '13 at 10:38
    
yes, if there is new line.. tr,sed and other also.. –  Rahul Patil Sep 2 '13 at 10:40
    
@slm thanks sir –  Rahul Patil Sep 2 '13 at 12:19

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