join Command: Tutorial & Examples

Join lines of two files on a common field

The join command is a utility in Linux that allows you to join the lines of two files based on a common field. It reads two input files and combines them based on the fields specified with the -1 and -2 options, which specify the field in each input file to be used for joining. By default, the join command outputs a line for each pair of input lines that have identical values in the specified fields.

Here is the basic syntax for using join:

join [options] file1 file2

Some common options for join include:

• -1 field: Specifies the field in file1 to use for joining.
• -2 field: Specifies the field in file2 to use for joining.
• -t char: Specifies the field separator character. The default is the tab character.
• -a file: Prints all lines from file, regardless of whether they match a line in the other file.
• -e string: Specifies a string to be printed in place of empty fields.
• -o format: Specifies the output format.

Here is an example of using join to join the lines of two files based on the first field:

join -t , -1 1 -2 1 file1.csv file2.csv

This command will join the lines of file1.csv and file2.csv based on the first field (which is separated by a comma).