I'd like to use grep to recursively search through a directory, using patterns listed in a file, then store each result in its own file for reference later.

I made an attempt (using this question as a guide) and came up with:


mkdir -p grep_results   # For storing results

echo "Performing grep searches.."
while IFS='' read -r line || [[ -n "$line" ]]; do
    echo "Seaching for $line.."
    grep -r "$line" --exclude-dir=grep_results . > ./grep_results/"$line"_infile.txt

echo "Done."

However, when I run it, the console hangs until I hit CTRL-C:

$ bash grep_search.sh search_terms.txt
Performing grep searches..

Where is the issue with this script? Or am I approaching this wrong?

  • 3
    on this line grep -r "$line" --exclude-dir=grep_results > ./grep_results/"$line"_infile.txt, I'm unable to see a file name to be looked into. That might be the reason why it hangs until ctrl-c is pressed. – MelBurslan Feb 17 '16 at 18:04
  • Well spotted! Unfortunately it's still not working. I modified my post to include the edited line. – PaleSaint Feb 17 '16 at 18:19
  • 1
    Similar to the previous issue, what is read reading from? Are you manually typing in search strings? Did you mean to run bash grep_search.sh < search_terms.txt? (Also note that bash can read patterns from a file. Check out the -f option.) – muru Feb 17 '16 at 18:23
  • That was the issue, I wasn't directing in search_terms.txt! Thanks muru, working as expected now – PaleSaint Feb 17 '16 at 18:25
  • @MelBurslan no, grep -r will be run on the current directory by default. That wasn't a problem. The -r flag makes grep run on all files in the current directory recursively. – terdon Feb 17 '16 at 18:37

There are a few issues here:

  1. The while loop isn't reading any input. The correct format is

    while read line; do ... ; done < input file


    some other command | while read ...

    Your loop is therefore hanging, waiting for input. You can test this by running your script and then typing anything and hitting enter (here, I entered foo):

    $ foo.sh 
    Performing grep searches..
    Searching for foo..

    You can improve this by adding a prompt to your read:

    while IFS='' read -p "Enter a search pattern: " -r line ...

    That will still run until you stop it with Ctrl+C though.

  2. The || [[ -n "$line" ]] (which means "OR the variable $line is not empty") is never executed. Since read hangs, the "OR" is never reached. I don't understand what you wanted it to do anyway. If you want to search for $line if $line is defined and use read if it is not, you'd need something like:

    if [[ -n "$line" ]]; then
         grep -r "$line" --exclude-dir=grep_results > ./grep_results/"$line"_infile.txt
        while IFS='' read -p "Enter a search pattern: " -r line || [[ -n "$line" ]]; do
          grep -r "$line" --exclude-dir=grep_results > ./grep_results/"$line"_infile.txt

    Here, if $line is not defined, you still need to enter it manually. A cleaner approach would be to either feed a file to the while loop:

    while IFS='' read -r line || [[ -n "$line" ]]; do
      grep -r "$line" --exclude-dir=grep_results > ./grep_results/"$line"_infile.txt
    done < list_of_patterns.txt
  • The intention was to direct list of patterns in a file at it - so multiple sets of patterns can be saved and used as and when. The || [[ -n "$line" ]] bit was there on recommendation from the answer to the question linked in my original post (prevents the last line from being ignored if it doesn't end with a \n (since read returns a non-zero exit code when it encounters EOF).) Your answer definitely helped me make sense of it though, thanks! – PaleSaint Feb 17 '16 at 18:46

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