CODEWITHSUNDEEP
shellsortingunixio-redirection
Mahagney Saleh
Mahagney Saleh

Reputation: 117

How to apply sort and uniq having the same input and output file in Unix?

I want to apply some operation(intersection and reunion) on two or more text files so after I put all rows together I have to apply sort and uniq on that file. The problem is that I want to have the same input and output file (-i doesn't work). Here is my code:

  nr_param=$#
    case $1 in

    '-r')
        if [ "$nr_param" = 3 ]
        then
            echo "reuniunea"
            rm -f reuniune1.txt
            cat $2 $3 >> reuniune1.txt
            sort <reuniune1.txt | uniq >reuniune.txt 
            rm -f reuniune1.txt
        else
            echo "parametri incorecti"
        fi;;
    '-i') 
        if [ "$nr_param" = 3 ]
        then
            echo "intersectia"
            rm -f intersectie.txt
            grep -Fx -f $2 $3 > intersectie.txt
        else
            echo "parametri incorecti"
        fi;;

Could you help me do the same thing without using an extra file? The same for grep if $2 would be "intersectie.txt".

Upvotes: 2

Views: 5986

Answers (1)

shellter
shellter

Reputation: 37288

Edit --

I wrote below when I was half asleep, ;-) and there's a great shortcut for your case

  sort -u -o file file

The -u option makes the sorted data uniq, and as mentioned below, -o file will save the output to any file your care to name, including the same name as the input.

If you want to do something like

  sort < file | uniq -c > uniqFileWithCounts

Then the first idea won't help you.

Don't kid yourself, even when you use sort -o file file to reuse the same filename for the sorted -o(utput), behind the scenes the system has to write all of the data to a tmp file and then rename to the file specified by -o file (Also sort is writing intermediate sort data to the /tmp dir and deletes that when the final output is complete).

So you're best bet is something like

sort <reuniune1.txt | uniq > uniqd.txt && mv uniqd.txt reuniune1.txt

This will only overwrite reuniune1.txt if the sort | uniq process exits without error.

IHTH

Upvotes: 6

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