How to extract lines from a text file that contains strings from a list in another file? [duplicate]

Question

I have a file containing population information for a bunch of towns. I have another file that is a list of the names of a subset of those towns. I want to select the population information from the first file using the second file. How would I do this?

Examples:

File 1: ma-towns.txt

Acton   Town    Middlesex   Open town meeting   21,924  1735  
Acushnet    Town    Bristol Open town meeting   10,303  1860  
Adams   Town    Berkshire   Representative town meeting 8,485   1778  
Agawam  City[4] Hampden Mayor-council   28,438  1855  
Alford  Town    Berkshire   Open town meeting   494 1773  
Amesbury    City    Essex   Mayor-council   16,283  1668  
Amherst Town    Hampshire   Representative town meeting 37,819  1775  

File 2: town-list.txt

Acton  
Adams  
Agawam 

Desired output would be

Acton   Town    Middlesex   Open town meeting   21,924  1735  
Adams   Town    Berkshire   Representative town meeting 8,485   1778  
Agawam  City[4] Hampden Mayor-council   28,438  1855   

Basically, as said generally, extract the line if it contains the string in one of the lines of file 2.

Answer 1

grep -f <(sed 's/.*/\^&\\>/' town-list.txt) ma-towns.txt

Explanation:

grep -f file reads file for a list of patterns to match against. We are searching in the ma-towns.txt list, using patterns from town-list.txt. Each separate line is treated as a new pattern, i.e. a new search term.

However, that's not quite enough, so I've included a sed to format the search terms like this:

^Acton\>
^Adams\>
^Agawam\>

The ^ makes grep only match that pattern at the start of a line, and the \> makes grep only match if the word ends at that point.

Together this ensures that the search term only looks at the beginning of the line (where the town names are), and that the search term must end where the town name ends.

---

The sed command itself runs a s (substitute) command, of the form s/search/replace/.

The search term .* matches a whole line. The replacement, \^&\\>, replaces it with a literal ^ character, followed by the original line, followed by the text \>.

---

What this answer does that the other does not:

• Handles town names beginning with a dash or containing backslashes (which is unlikely, but if the input is taken from a user you don't want them to be able to break your scripts in unpredictable ways). Note that both answers treat town names as a regex rather than a literal search term.
• Outputs the towns in the original order as specified in ma-towns.txt
• Performs better
• Searches the beginning of the line for the town name, not just anywhere in the line
• Does not match a town if only a substring matches (e.g. Waterloo will not match Waterlooville)

Answer 2

This will read the lines of file2 and parse file1 with grep using the lines :

while read line; do
  grep "${line}" file1
done < file2