COMM(1) General Commands Manual COMM(1)

comm — select or reject lines common to two files

comm [-123] file1 file2

The comm utility shall read file1 and file2, which should be ordered in the current collating sequence, and produce three text columns as output: lines only in file1; lines only in file2; and lines in both files. If the lines in both files are not ordered according to the collating sequence of the current locale, the results are unspecified.

The comm utility shall conform to the utility argument syntax guidelines described in 2.10.2. The following options shall be supported by the implementation:

Suppress the output column of lines unique to file1.

Suppress the output column of lines unique to file2.

Suppress the output column of lines duplicated in file1 and file2.

The following operands shall be supported by the implementation:

file1

A pathname of the first file to be compared. If file1 is −, the standard input is used.

file2

A pathname of the second file to be compared. If file2 is −, the standard input is used. If both file1 and file2 refer to standard input or to the same special, block special, or character special file, the results are undefined.

The standard input shall be used only if one of the file1 or file2 operands refers to standard input. See Input Files.

The input files shall be text files.

The following environment variables shall affect the execution of comm:

This variable shall determine the locale to use for the locale categories when both LC_ALL and the corresponding environment variable (beginning with LC_ ) do not specify a locale. See 2.6.

This variable shall determine the locale to be used to override any values for locale categories specified by the settings of LANG or any environment variables beginning with LC_.

This variable shall determine the locale for the interpretation of sequences of bytes of text data as characters (e.g., single- versus multibyte characters in arguments and input files).

This variable shall determine the locale for the collating sequence comm expects to have been used when the input files were sorted.

This variable shall determine the language in which messages should be written.

Default.

The comm utility shall produce output depending on the options selected. If the −1, −2, and −3 options are all selected, comm shall write nothing to standard output. If the −1 option is not selected, lines contained only in file1 shall be written using the format: "%s\n", <line in file1> If the −2 option is not selected, lines contained only in file2 shall be written using the format: "%s%s\n", <lead>, <line in file2> where the string <lead> is: <tab> if the −1 option is not selected, or null string if the −1 option is selected. If the −3 option is not selected, lines contained in both files shall be written using the format: "%s%s\n", <lead>, <line in both> where the string <lead> is: <tab><tab> if neither the −1 nor the −2 option is selected, or <tab> if exactly one of the −1 and −2 options is selected, or null string if both the −1 and −2 options are selected. If the input files were ordered according to the collating sequence of the current locale, the lines written shall be in the collating sequence of the original lines.

Used only for diagnostic messages.

None.

None.

The comm utility shall exit with one of the following values:

All input files were successfully output as specified.

An error occurred.

Default.

If the input files are not properly presorted, the output of comm might not be useful. If a file named posix.2 contains a sorted list of the utilities in this standard, a file named xpg3 contains a sorted list of the utilities specified in X/Open Portability Guide Issue 3, and a file named svid89 contains a sorted list of the utilities in the System V Interface Definition Third Edition: comm -23 posix.2 xpg3 | comm -23 - svid89 would print a list of utilities in this standard not specified by either of the other documents, comm -12 posix.2 xpg3 | comm -12 - svid89 would print a list of utilities specified by all three documents, and comm -12 xpg3 svid89 | comm -23 - posix.2 would print a list of utilities specified by both and , but not specified in this standard.

None.

September 1991 posix.fail