v1 indicates to display the non-matching records of file1. join gives you one more option with which we can only see the records for which there is no match: o : tells for which all missing fields this should be substituted.Ģ.2 - the seconf field of the second fileĥ. e : tells what to substitute in case of missing fields, NULL in this case. $ join -t"," -1 2 -a 1 -a2 -e ' NULL' -o '0,1.1,2.2' a1 a2ĭoes not this look like a proper database output with all the missing fields replaced with NULL!!! Let us understand what these options are for: The name came in place of the balance field since there is no balance record present in file a1. This output, if you notice, is not very user friendly, especially the last record. a option is to display the unmatchable or unpairable lines as well. In outer joins, the records for which there is no matching record, the missing fields will be displayed blank. Join command can also be simulated to do kind of outer join which we do in Oracle. Same output!! Join command, by default, displays only those records for which the matches are found. Now, lets try to execute the same join command as earlier: The last record in both the files does not have a matching record in the other files. Sometimes, we can have files where a file can have a record for which there is no matching record in the other file. Note: Keep in mind, in the above example, we need not have specified the key for the second file since the key is the first column itself. So, whenever we have files in which the key is not the first column, this is how the join needs to be done. 2 1 : use the first column(1) as the key for join in the second file(-2) 1 2 : use the second column(2) as the key for join in the first file(-1) What if the key on which the join is to happen is not present in the first column? ![]() Note: In case of files having delimiter, to use the "join" command, both the files should contain the same delimiter.ģ. Since comma is the delimiter, we specify it along with -t. The default join field is the first, delimited by blanks. FILE1 FILE2 DESCRIPTION top For each pair of input lines with identical join fields, write a line to standard output. Like the sort command, "-t" is the option we use to specify the delimiter. join - join lines of two files on a common field SYNOPSIS top join OPTION. Let us update the files with comma delimiter. Most of the times, files contain some delimiter to separate the columns. Note: When using join command, both the input files should be sorted on the KEY on which we are going to join the files.Ģ.
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