How can I get all lines that are: in both of two files (set intersection) or in only one of two files (set subtraction).
Use the comm(1) command.
# Bash # intersection of file1 and file2 comm -12 <(sort file1) <(sort file2) # subtraction of file1 from file2 comm -13 <(sort file1) <(sort file2)
Read the comm manpage for details.
If for some reason you lack the core comm program, you can use these other methods:
- An amazingly simple and fast implementation, that took just 20 seconds to match a 30k line file against a 400k line file for me.
# intersection of file1 and file2 grep -xF -f file1 file2 # subtraction of file1 from file2 grep -vxF -f file1 file2
- It has grep read one of the sets as a pattern list from a file (-f), and interpret the patterns as plain strings not regexps (-F), matching only whole lines (-x).
- Note that the file specified with -f will be loaded into memory, so it doesn't scale for very large files.
It should work with any POSIX grep; on older systems you may need to use fgrep rather than grep -F.
- An implementation using sort and uniq:
# intersection of file1 and file2 sort file1 file2 | uniq -d (Assuming each of file1 or file2 does not have repeated content) # file1-file2 (Subtraction) sort file1 file2 file2 | uniq -u # same way for file2 - file1, change last file2 to file1 sort file1 file2 file1 | uniq -u
- Another implementation of subtraction:
cat file1 file1 file2 | sort | uniq -c | awk '{ if ($1 == 2) { $1 = ""; print; } }'- This may introduce an extra space at the start of the line; if that's a problem, just strip it away.
- Also, this approach assumes that neither file1 nor file2 has any duplicates in it.
- Finally, it sorts the output for you. If that's a problem, then you'll have to abandon this approach altogether. Perhaps you could use awk's associative arrays (or perl's hashes or tcl's arrays) instead.