grep : find bigger string in small string

Question

I am writing a small shell script to receive an input and match against a text file.

However, the input would be a bigger string than the string in the file, against which I want a match.

User input:

abc-de-ef-gh1

Text in file:

This is test,-de-ef-gh,This is test

I want a positive result if I grep user-input with existing file.

How can I achieve this? I couldn't do it with grep.

Answer 1

You have a file with patterns. grep can read the patterns with its -f option. If you want to check whether a string, $input, matches a pattern in patterns.txt, you may do

printf '%s\n' "$input" |
if grep -q -f patterns.txt; then
    echo 'matches'
else
    echo 'does not match'
fi

This would run grep over the contents of the string with the patterns in patterns.txt. In bash you could instead use a here-string:

if grep -q -f patterns.txt <<<"$input"; then
    echo 'matches'
else
    echo 'does not match'
fi

The -q stops grep from producing output (we're only interested in the exit status).

If the patterns are fixed strings (not regular expressions), use -F with grep in addition to the other flags (grep -qF -f ...).

Answer 2

Using bash, cut and grep:

read -p "Hey user, input something: " $n
printf "Match "
grep -m 1 -q -f <(cut -d, -f2 file) <<< "$n" || printf "not "
printf "found.\n"

Notes:

• It's impossible to search for a longer string in a shorter, but this is really about finding whether shorter strings in file match a longer string.
• cut is used to extract the middle field from file
• grep searches for that middle field in the user input string.
• printf provides some feedback.