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I use ubuntu 14.4, and attempt to redirect the output of grep command to a file, but I keep getting this error:

grep: input file 'X' is also the output

I've searched for this issue and just found out that it was a bug in ubuntu 12.4 and there is not any describe about, can anybody help me to figure out this problem?

I run the following command:

grep -E -r -o -n r"%}(.*){%" > myfile
share|improve this question
    
If you are trying grep pattern file > file then it doesn't work. You cannot use the same file as input and output for grep. –  jimmij Oct 25 '14 at 21:29
    
i add my command ! thanks for hint , but when i try to use a file in other path the does not predicate it and i cant do that ! –  Kasra Oct 25 '14 at 21:34
    
for example with ../f i get this bash: ../f.txt: Permission denied –  Kasra Oct 25 '14 at 21:37
    
show full command, what is your input file, or are you using the pipe? –  jimmij Oct 25 '14 at 21:42
    
Yes, please show the entire command. It's unclear what you're asking us at this point, so unlikely that anyone will be able to help you further. –  slm♦ Oct 25 '14 at 21:43

1 Answer 1

up vote 2 down vote accepted

It is not possible to use the same file as input and output for grep. You may consider the following alternatives:

  • temporary file

    grep pattern file > tmp_file
mv tmp_file file

  • sed

    sed -i -n '/pattern/p' file

  • put whole file in the variable (not bright idea for large files)

    x=$(cat file); echo "$x" | grep pattern > file
share|improve this answer
    
sed can be more portable sed -i '/pattern/!d' file –  Costas Oct 25 '14 at 21:53
    
But in the case OP wants sed -i -n 's/.*\(pattern\).*/\1/p' file –  Costas Oct 25 '14 at 22:20
    
@Costas you are right, the question was edited and additional info added so one can polish sed syntax as well. –  jimmij Oct 25 '14 at 22:35

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