Convert list into a regexp that grep likes But lets be on the safe side.Īssume : working sed ,one of od OR hexdump OR xxd (from vim package) is available.ġ. Under normal situations, grep -rf patternfile.txt /some/dir/ is the way to go.Ī file containing a list of all the strings to be searchedĪssumptions : gnu coreutil not available. I assume (for some reason) the system is broken, and escapes do not work as expected. Also, if you find yourself using this often then you can convert this into a shell script that takes the file names as arguments.By reading, I assume we can not use the gnu coreutil, and egrep is not available. It can work for small files (maybe around 1000 lines or so). However, the efficiency can depend very much on the size of your input files. The command above can sort and compare 4 different files. However the command used in the above section, the one with cat, sort and uniq can be pretty scalable.īash$ cat <(sort file1 | uniq) <(sort file2 | uniq) <(sort file3 | uniq) <(sort file4 | uniq) | sort | uniq -d If you want to compare more than two files, then comm command is not much help. The comm command and the commands above works with two files. Remember that for large files, this might not be so efficient…īash$ cat <(sort file1 | uniq) <(sort file2 | uniq) | sort | uniq -d More than two files The solution is to sort and remove duplicate of each individual file before merging them for the final sort and unique check. If the same line occurs twice or more with in the same file (say, file1) then it will be printed as a common line which is not correct. It assumes that each line is unique with in the file. However, there is a small caveat with this approach. Without the -d option, it will print the unique lines whether duplicated or not which is not what you want. The -d option in uniq command is important in this context because that specifies that it should show only repeated or duplicate lines. To start with, we can do something like this… You can use a combination of cat, sort and uniq to achieve the same result. Well, comm is not the only command that can be used to find common lines. This will also take away the hassle of having to create intermediate files.īash$ comm -12 <(sort file1) <(sort file2) The following set of three commands will allow you to sort and find common lines.īeing Linux, you can easily combine the above three commands to a single line. The Linux command sort will allow you to sort text files.
If your files are not sorted, then obviously the first option is to sort the files and then run the comm command. Beware though that it can get a little tricky to interpret the results. In this case, you want the command to consider lines to be same only if it occurs in the same place in the file. This can be useful when comparing certain files, such as log files. This option ( –nocheck-order) is useful when you want comm to treat the input files as sorted. You can also turn this check off using the option –nocheck-order.īash$ comm -nocheck-order -12 file1 file2
You can force this check using the command line option –check-order. The comm command by default checks that the files are in sorted order. So, if you like to see only lines that are common to both files, then you can suppress the printing of columns 1 and 2 as shown in the example below. Here, file1 and file2 are example file names. Using the command without any options as shown below will produce a three column output, the first column shows lines that are unique to file1, the second column are lines that are unique to file2 and the third column shows lines that are common to both files. If you have two files that are already sorted, then you can use the comm command directly on these files. Straight out of the box, the comm command has some (mainly, two) limitations: It works only with pre-sorted files and it works with only two files. In this post, we will look at comm command in detail as we are trying to find common or similar lines in files. Also, it is more feature rich of the two commands. diff is the more popular of the two, as the most common use case is to find differing lines (I think!). These commands lets you find either the common lines or the differing lines: comm and diff. There are two related Linux commands that lets you compare files from command line. If most of the lines (say, more than 50%) in the files are the same then you probably are looking for all differing lines and vice-versa. It all depends on how closely related the two files are. When comparing files, it is usually one of two things that you are trying to achieve…1) Find all common lines in both files or all files and/or 2) Find all differing lines in both files. Let’s say you have two or more text files that you want to compare.
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