Compare the content of two different files

Question

For example, `file1.txt, contains only variables:

a
b
d
c

file2.txt contains < , variable and path:

< a /x/y/1.c
< c /x/d/7.h
< f /x/c/6.s
< b /x/v/8.mk
< t /x/1.h
< d /x/5.so

file1.txt variables should be compared with file2.txt . If a match is found, the complete variable and path should be printed from file2.txt .

Expected output:

< a /x/y/1.c
< b /x/v/8.mk
< d /x/5.so
< c /x/d/7.h

I tried with comm -3 file1.txt file2.txt , but it is not effectively working.

diff can't be used in my case.

Answer 1

if the lines in file2.txt not start with <, you can use this;

join <(sort file1.txt) <(sort file2.txt)

if starts with < char, you can use this;

join -11 -22 <(sort file1.txt) <(sort file2.txt)

Eg;

user@host:/tmp$ join -11 -22 <(sort file1.txt) <(sort file2.txt)
a < /x/y/1.c
b < /x/v/8.mk
c < /x/d/7.h
d < /x/5.so

-11 means file1.txt and first column, -22 means file2.txt and second column (after "<" char)

Answer 2

Solution for when the keys are not anywhere in the path: Try this

cat file2.txt | grep -f file1.txt

Switch the file names as need.

Answer 3

You asked for shell but I would answer via python

import sys

with open(sys.argv[1], "r") as f:
    d = dict((e.rstrip().split()[1], e) for e in f)

with open(sys.argv[2], "r") as f:
    for e in f:
        e = e.rstrip()
        if e in d:
            print(d[e], end="")

If you saved it to run.py , you can call it such that

python3 run.py file2.txt file1.txt > output.txt

It also preserves the order of file1.txt compared to sorting solutions but loads second file into memory.

Answer 4

AWK is good for these things:

$ awk 'NR == FNR {keys[$0] = 1; next}keys[$2]' file1.txt file2.txt
< a /x/y/1.c
< c /x/d/7.h
< b /x/v/8.mk
< d /x/5.so

Basically file1.txt is buffered in the keys array. And then each line from file2 is printed if column 2 is in said array: