Ubuntu – Using grep to print line numbers

grep

I would like to use the grep command to print a line number for the string I'm searching for. However, when I used the command grep -n it prints the line number with a colon : next to it. Is there any way I can use the same grep -n command to print a line number with it being followed by the : colon?

$ grep -n 'Captain' sometextfile.txt
3: Captain America

I would like it to instead print,

3 Captain America

(without the ':' )

Any suggestions??

Best Answer

You can use sed along with grep to achieve this.

grep -n 'Captain' sometextfile.txt | sed 's/:/ /'

This sed command finds the pattern : and replaces it with (a space).

General Syntax - sed 's/find/replace/'

This method will replace only the first occurence of : in each line with . Therefore, even if a line in the text file contains :, it will remain unaffected.

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Ubuntu – grep recursively for specific files

You are getting these Permission denied errors because there are some python files that your user does not have permission to read, so grep is not working for those files (you can't search them).

You want to "get rid of" the Permission denied errors.

You can add 2>/dev/null to the end of your command like this:
```
grep -rn --include="*.py" "search-pattern" 2>/dev/null
```
This suppresses all error messages, so you won't see the Permission denied errors popping up. But this obviously still means that grep is not searching those files, so if they do contain your search-pattern, you won't see them in the output.

Explanation:
In Linux, there are three things called file descriptors: stdin, stdout, stderr. If you run a command and it gives you an error, the error is written to the file descriptor stderr. By default, stderr outputs the errors to the terminal. So what we can do is redirect the errors, i.e. we redirect stderr somewhere else instead of the terminal. We redirect stuff in Linux by using the > sign. So where are we going to redirect stderr? To /dev/null. /dev/null is a special file; think of it as a black hole. Anything you redirect to it gets thrown away. Finally, we refer to stderr as simply the number 2. So 2>/dev/null tells Linux to redirect 2 to /dev/null. 1 means stdout (which is the normal output of a command, i.e. not errors). So, for example, if you wanted to save the actual output of your grep command to a file rather than have it displayed in the terminal, you can use 1>/path/to/filename, which will redirect stdout to that file.
Use sudo with your command, assuming that you have the privileges:
```
sudo grep -rn --include="*.py" "search-pattern"
```
If your username has root privileges (i.e. if you're an administrator on the machine), using sudo before a command runs it as the root user, so you will never get the Permission denied errors and grep will search those files and output the search-pattern if it finds it inside them.

Ubuntu – Repeat whole line matches with grep for multiple instances on the same line

grep doesn't have counter for matches, only -c counter for lines that have the match, but we can use awk to do that. As far as I understand , you want to print the line that matches x number of times based on the amount of matches. Well, here it is:

$ awk '{for(i=1;i<=NF;i++) if($i=="banana") counter++;for(j=1;j<=counter;j++) print NR,$0;counter=0 }' input.txt         
1 There is one banana here
2 There are two banana banana here
2 There are two banana banana here
3 There are three banana banana banana here
3 There are three banana banana banana here
3 There are three banana banana banana here
4 Basically there is no limit to how many banana banana banana banana banana banana banana we can have
4 Basically there is no limit to how many banana banana banana banana banana banana banana we can have
4 Basically there is no limit to how many banana banana banana banana banana banana banana we can have
4 Basically there is no limit to how many banana banana banana banana banana banana banana we can have
4 Basically there is no limit to how many banana banana banana banana banana banana banana we can have
4 Basically there is no limit to how many banana banana banana banana banana banana banana we can have
4 Basically there is no limit to how many banana banana banana banana banana banana banana we can have

Basic idea here is that we loop over each word in a line, and count matches. If there's a match we increment counter and then use that counter to print the same line in a loop. Finally counter is reset and process repeats

Best Answer

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Ubuntu – grep recursively for specific files

Ubuntu – Repeat whole line matches with grep for multiple instances on the same line

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