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grep: input file 'X' is also the output

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.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty{ margin-bottom:0;
}

7

2

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

shell ubuntu command-line grep io-redirection

share|improve this question

edited Oct 25 '14 at 23:18

jimmij

33.4k88 gold badges7878 silver badges115115 bronze badges

asked Oct 25 '14 at 21:24

KasrâmvdKasrâmvd

49411 gold badge55 silver badges1515 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  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 !
  
  – Kasrâmvd
  Oct 25 '14 at 21:34
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  for example with ../f i get this bash: ../f.txt: Permission denied
  
  – Kasrâmvd
  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
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Now I understand that you are actually greping recursively the whole directory structure and want to append the result to the file which already exists in this structure. The problem is that shell (bash, zsh, whatever) first performs redirections and only then goes back to commands (grep in this example). It means that grep in command grep pattern file > file sees already empty file, so has nothing as input. However if you use >> instead of > then the file is not empty, but grep throws error anyhow as it may lead to recursive processing the same line (pattern) over and over again.
  
  – jimmij
  Oct 25 '14 at 22:22
  

  
  
  
  

 | 
show 3 more comments

7

2

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

shell ubuntu command-line grep io-redirection

share|improve this question

edited Oct 25 '14 at 23:18

jimmij

33.4k88 gold badges7878 silver badges115115 bronze badges

asked Oct 25 '14 at 21:24

KasrâmvdKasrâmvd

49411 gold badge55 silver badges1515 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  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 !
  
  – Kasrâmvd
  Oct 25 '14 at 21:34
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  for example with ../f i get this bash: ../f.txt: Permission denied
  
  – Kasrâmvd
  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
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Now I understand that you are actually greping recursively the whole directory structure and want to append the result to the file which already exists in this structure. The problem is that shell (bash, zsh, whatever) first performs redirections and only then goes back to commands (grep in this example). It means that grep in command grep pattern file > file sees already empty file, so has nothing as input. However if you use >> instead of > then the file is not empty, but grep throws error anyhow as it may lead to recursive processing the same line (pattern) over and over again.
  
  – jimmij
  Oct 25 '14 at 22:22
  

  
  
  
  

 | 
show 3 more comments

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

shell ubuntu command-line grep io-redirection

share|improve this question

edited Oct 25 '14 at 23:18

jimmij

33.4k88 gold badges7878 silver badges115115 bronze badges

asked Oct 25 '14 at 21:24

KasrâmvdKasrâmvd

49411 gold badge55 silver badges1515 bronze badges

grep -E -r -o -n r"%}(.*){%" > myfile

share|improve this question

edited Oct 25 '14 at 23:18

jimmij

33.4k88 gold badges7878 silver badges115115 bronze badges

asked Oct 25 '14 at 21:24

KasrâmvdKasrâmvd

49411 gold badge55 silver badges1515 bronze badges

share|improve this question

edited Oct 25 '14 at 23:18

jimmij

33.4k88 gold badges7878 silver badges115115 bronze badges

asked Oct 25 '14 at 21:24

KasrâmvdKasrâmvd

49411 gold badge55 silver badges1515 bronze badges

edited Oct 25 '14 at 23:18

jimmij

33.4k88 gold badges7878 silver badges115115 bronze badges

edited Oct 25 '14 at 23:18

jimmij

33.4k88 gold badges7878 silver badges115115 bronze badges

asked Oct 25 '14 at 21:24

KasrâmvdKasrâmvd

49411 gold badge55 silver badges1515 bronze badges

asked Oct 25 '14 at 21:24

KasrâmvdKasrâmvd

49411 gold badge55 silver badges1515 bronze badges

3 Answers
3

active

oldest

votes

6

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

answered Oct 25 '14 at 21:45

jimmijjimmij

33.4k88 gold badges7878 silver badges115115 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  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
  
  
  

  
  
  
  

add a comment | 

4

You can use the --exclude field in your grep command like so:

grep  --exclude=myfile  -Eron  r"%}(.*){%"  >  myfile

share|improve this answer

answered Sep 4 '15 at 13:23

AaronDanielsonAaronDanielson

14133 bronze badges

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Make sure myfile is unique as it only applies to the file's basename. You don't want to skip files with the same name in other directories.
  
  – Walf
  Mar 7 '17 at 0:45
  

  
  
  
  

add a comment | 

1

I found a way in bash:
cat >> IN_OUTPUT_FILE <<< "$(grep something IN_OUTPUT_FILE)"

The command in <<<"..." will be executed first.

share|improve this answer

answered 54 mins ago

osexp2003osexp2003

12144 bronze badges

add a comment | 

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6

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

answered Oct 25 '14 at 21:45

jimmijjimmij

33.4k88 gold badges7878 silver badges115115 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  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
  
  
  

  
  
  
  

add a comment | 

6

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

answered Oct 25 '14 at 21:45

jimmijjimmij

33.4k88 gold badges7878 silver badges115115 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  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
  
  
  

  
  
  
  

add a comment | 

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

answered Oct 25 '14 at 21:45

jimmijjimmij

33.4k88 gold badges7878 silver badges115115 bronze badges

share|improve this answer

answered Oct 25 '14 at 21:45

jimmijjimmij

33.4k88 gold badges7878 silver badges115115 bronze badges

answered Oct 25 '14 at 21:45

jimmijjimmij

33.4k88 gold badges7878 silver badges115115 bronze badges

answered Oct 25 '14 at 21:45

jimmijjimmij

33.4k88 gold badges7878 silver badges115115 bronze badges

4

You can use the --exclude field in your grep command like so:

grep  --exclude=myfile  -Eron  r"%}(.*){%"  >  myfile

share|improve this answer

answered Sep 4 '15 at 13:23

AaronDanielsonAaronDanielson

14133 bronze badges

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Make sure myfile is unique as it only applies to the file's basename. You don't want to skip files with the same name in other directories.
  
  – Walf
  Mar 7 '17 at 0:45
  

  
  
  
  

add a comment | 

4

You can use the --exclude field in your grep command like so:

grep  --exclude=myfile  -Eron  r"%}(.*){%"  >  myfile

share|improve this answer

answered Sep 4 '15 at 13:23

AaronDanielsonAaronDanielson

14133 bronze badges

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Make sure myfile is unique as it only applies to the file's basename. You don't want to skip files with the same name in other directories.
  
  – Walf
  Mar 7 '17 at 0:45
  

  
  
  
  

add a comment | 

You can use the --exclude field in your grep command like so:

grep  --exclude=myfile  -Eron  r"%}(.*){%"  >  myfile

share|improve this answer

answered Sep 4 '15 at 13:23

AaronDanielsonAaronDanielson

14133 bronze badges

grep  --exclude=myfile  -Eron  r"%}(.*){%"  >  myfile

share|improve this answer

answered Sep 4 '15 at 13:23

AaronDanielsonAaronDanielson

14133 bronze badges

answered Sep 4 '15 at 13:23

AaronDanielsonAaronDanielson

14133 bronze badges

answered Sep 4 '15 at 13:23

AaronDanielsonAaronDanielson

14133 bronze badges

1

I found a way in bash:
cat >> IN_OUTPUT_FILE <<< "$(grep something IN_OUTPUT_FILE)"

The command in <<<"..." will be executed first.

share|improve this answer

answered 54 mins ago

osexp2003osexp2003

12144 bronze badges

add a comment | 

1

I found a way in bash:
cat >> IN_OUTPUT_FILE <<< "$(grep something IN_OUTPUT_FILE)"

The command in <<<"..." will be executed first.

share|improve this answer

answered 54 mins ago

osexp2003osexp2003

12144 bronze badges

add a comment | 

I found a way in bash:
cat >> IN_OUTPUT_FILE <<< "$(grep something IN_OUTPUT_FILE)"

The command in <<<"..." will be executed first.

share|improve this answer

answered 54 mins ago

osexp2003osexp2003

12144 bronze badges

share|improve this answer

answered 54 mins ago

osexp2003osexp2003

12144 bronze badges

answered 54 mins ago

osexp2003osexp2003

12144 bronze badges

answered 54 mins ago

osexp2003osexp2003

12144 bronze badges