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Neeraj Gupta
Asked: 2011-03-27 06:22:07 +0800 CST

Grep, ignore warnings

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I am trying to find the installation directory of a particular package. I have a certain keyword using which I am trying to find a particular file.

During grep, I only want to include cpp or h file type. I do not want the grep to show warnings like Permission Denied or Could not find the Directory. I just want it to display matched files, nothing else. Please suggest how can I do this?

At present I am using

grep "My term" -ir --exclude-dir="\.svn" --include=*.{cpp,h} ./
search

5 Answers

  1. Best Answer

    Those warnings are directed to the stderr stream, as opposed to the standard out file descriptor. You can silence the stderr output by adding 2>/dev/null to the end of your command.

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  2. More directly than filtering the warnings you can disable them by adding -s:

    grep "My term" -sir --exclude-dir="\.svn" --include=*.{cpp,h} ./

    There are some compatibility issues with this option. However, this shouldn't be a problem for personal use.

    -s, --no-messages: Suppress error messages about nonexistent or unreadable files. Portability note: unlike GNU grep, 7th Edition Unix grep did not conform to POSIX, because it lacked -q and its -s option behaved like GNU grep's -q option. USG-style grep also lacked -q but its -s option behaved like GNU grep. Portable shell scripts should avoid both -q and -s and should redirect standard and error output to /dev/null instead. (-s is specified by POSIX.)

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  3. I used to get a ton of annoying messages like this:

    grep: commands: Is a directory
grep: events: Is a directory
grep: views: Is a directory

    The reason is that the --directories flag is defaulted to read. I changed it to recurse; if you don't want it to automatically do a recursive search you can use skip instead.

    The easiest way to handle this all the time is to set it in an environment variable. In ~/.bash_profile or ~/.bashrc depending on your distro:

    export GREP_OPTIONS='--directories=recurse'

    Now it automatically suppresses those messages any time I use grep.

    Another option is the --no-messages flag, shorthand -s. This will also get rid of the Is a directory messages, but it also suppresses other messages which might be more useful. For example, if you're doing a nested search in */*/* and no such file of that pattern exists, it won't tell you that.

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  4. Alternative approach instead of doing grep recursively with -ir would be to let find command (which is recursive by default) handle the permissions with -readable flag and path's to exclude with -not -path "*.svn*" flags, and then pass the file to grep. Excluding directories is done via -type f for finding only regular files.

    $ find . -not -path "*.svn*" -type f -name "*.cpp" -or -name "*.h"  -readable -exec grep "my terms" "{}" \;
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  5. When doing recursive searches in specific files, you are much better off using ack-grep. The syntax here would be:

    ack-grep -i "My term" --cpp --h

    To remove the permission error messages, you may want to run the same command with sudo:

    ack-grep -i "My term" --cpp --h

    But eventually, if you want to search installed packages, look at those various options: https://www.google.com/search?q=ubuntu%20search%20inside%20installed%20packages

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