How to use grep when file does not contain the string?

How to use grep when file does not contain the string?

In my bash script I’m trying to print a line if a certain string does not exist in a file. if grep -q “$user2” /etc/passwd; then echo “User does exist!!” This is how I wrote it if I wanted the string to exist in the file but how can I change this to make it print “user does not exist” if the user is not found in the /etc/passwd file?

How can I search a file using grep?

By default, the grep command displays name of files containing the search pattern (as well as matched lines). This is quite logical, as that’s what expected of this tool. However, there might be cases wherein the requirement could be to get names of those files that do not contain the searched pattern.

How to check if file does not contain a string?

You can use the grep option “-L / –files-without-match”, to check if file does not contain a string: An alternative is to look for the exit status of grep. For example:

How to avoid stack overflow with grep regex?

If you need to “match A but not B” you usually use pipes: Try this. It uses negative lookbehind to ignore the line if it is preceeded by 1.2.3.4. Hope that helps! Thanks for contributing an answer to Stack Overflow!

Can a grep find text in a binary file?

Yes, it’s not a standard text file, I admit, but grep is able to find strings also in binary file. Indeed it was able to found the word in two jar files in the project. Why it failed with this text one?

What to do when grep fails to find a word?

I cloned with git the source code of a project, and I used grep to find a word in the entire project, SchemaHandler. grep failed to find the word in this strange code file: https://github.com/yawlfoundation/yawl/blob/master/src/org/yawlfoundation/yawl/schema/YDataValidator.java

What is a list of patterns in grep?

It’s just a list of patterns like the “1\\.2\\.3\\.4.*Has exploded” part I am passing, in a loop, so I can’t pass “-v” for example. I am confused trying to do the inverse of the above, and NOT match lines with a certain IP address and error so “!1.2.3.4.*Has exploded” will match syslog lines for anything other than 1.2.3.4 telling me it has exploded.

What does grep stand for in Linux command line?

Grep is an acronym that stands for Global Regular Expression Print. Grep is a Linux / Unix command line tool used to search for a string of characters in a specified file.

What does it mean when a line is not returned in grep?

You’re grepping for “not a”, which means any lines containing something that is not an a will be returned. Lines which contain only one or more a ‘s will not be returned. Try using grep -v a file instead.

How to command grep not to display the searched lines?

you can use cut command for this purpose. Here -c6- option means print from 6th to last character. You can use grep and just grep: -o, –only-matching Print only the matched (non-empty) parts of a matching line, with each such part on a separate output line.

How to print only one word per line in grep?

(allowing only one occurrence per line; if there are more than one, only the rightmost one will be displayed). That won’t print the file names. For that, you could use awk instead: The * operator in regular expressions means “zero or more”, so grep is perfectly happy to satisfy that condition by using “zero” additional characters.

How can I have grep not print out’no such file or directory’errors?

You can use the -s or –no-messages flag to suppress errors. If you are grepping through a git repository, I’d recommend you use git grep. You don’t need to pass in -R or the path.

Can a grep return true or false or there alternative?

In an if statement, a zero exit code is mapped to “true” and a non-zero exit code is mapped to false. In addition, grep has a -q argument to not output the matched text (but only return the exit status code)

When does grep return a different exit code?

grep returns a different exit code if it found something (zero) vs. if it hasn’t found anything (non-zero). In an if statement, a zero exit code is mapped to “true” and a non-zero exit code is mapped to false. In addition, grep has a -q argument to not output the matched text (but only return the exit status code)