1

I have the following script:

#!/bin/bash
result=$(grep "pattern 1\|pattern 2\|pattern 3\|pattern 4\|pattern 5\|pattern 6\|pattern 7\|pattern 8" file_data.dat)

if [ -n "$result" ]; then
    printf '%s\n' "$result"
else
    printf 'No match found for pattern "%s"\n' "$pattern"
fi

It works but it has an issue, if there is no match for one of the patterns, I want to know which pattern did not match.

I also tried with:

#!/bin/bash

if
        grep "pattern 1\|pattern 2\|pattern 3\|pattern 4\|pattern 5\|pattern 6\|pattern 7\|pattern 8" file_data.dat
then
echo "All patterns found"
else
echo "Missing pattern"
fi

But it has same issue.

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7
  • 2
    I see no expected behavior, nor explanation as to how it fails to work. Commented May 5, 2021 at 11:03
  • yes, I want it to report which pattern didn't find.Never used awk for these type of cases but I will try to investigate. Commented May 5, 2021 at 11:31
  • 1
    Your grep runs over the file (once) and prints all lines that match at least one of the patterns, so the output is only empty (or the exit code not 0) if none of the patterns match. Perhaps you rather want to loop over the patterns and check them separately? Commented May 5, 2021 at 11:42
  • 1
    Please edit your question and explain what you want to happen. What is the desired output here? Do you want to see matching lines? Do you want to see counts of matches? Should the script actually fail if no matches are found? Or fail if one match is not found? Can the matches be on the same line? Commented May 5, 2021 at 12:27
  • 1
    awk would be able to count the number of matches for each pattern, and the actual matched lines if required, and show the counts for each pattern in an END clause. It could even tell you all the actual strings that matched each instance of each pattern, if you wished. It can do that in one pass through the file, too, instead of one pass per pattern. If you can refine the requirement, I can post the code. Commented May 5, 2021 at 12:49

1 Answer 1

Reset to default
4

Consider this:

#!/bin/bash -
patterns=('pattern1' 'pattern2' 'pattern3' 'pattern4' '...')

for pat in "${patterns[@]}"; do
    if ! grep -q -e "$pat" infile; then
        ((missed++))
        printf '%s\n' "pattern $pat not found"
    fi
done
if [[ -z "$missed" ]]; then
    printf '%s\n' 'all patterns were found'
else
    printf 'Among %d patterns, %d patterns were not found\n' "${#patterns[@]}" "$missed"
fi

Hold all the patterns into an array in patterns=( ... ), then loop over the patterns in the array and check with grep for the matching of that pattern. If the pattern matches, then quit silently, else report that the pattern wasn't found and increment the missed temporary variable by 1.

Outside of the loop we checks if that temporary variable was not set, that means all patterns were found and so reported, else print the count of missed patterns among total patterns.

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