> For the complete documentation index, see [llms.txt](https://book.bsdcn.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://book.bsdcn.org/man/man1/comm.1.md).

# comm.1

`comm` — 选择或拒绝两个文件中共同的行

## 名称

`comm`

## 概要

`comm [-123i] file1 file2`

## 描述

`comm` 实用程序读取 `file1` 和 `file2`（两者应已按词法排序），并产生三列文本输出：仅在 `file1` 中的行；仅在 `file2` 中的行；以及两个文件中都有的行。

文件名 \`\`-'' 表示标准输入。

以下选项可用：

**`-1`** 禁止打印第 1 列，即仅在 `file1` 中的行。

**`-2`** 禁止打印第 2 列，即仅在 `file2` 中的行。

**`-3`** 禁止打印第 3 列，即两个文件中共同的行。

**`-i`** 行比较时不区分大小写。

每列前面将附加若干制表符，数量等于正在打印的、编号小于该列的列数。例如，如果第 2 列被禁止打印，则第 1 列打印的行前面没有任何制表符，而第 3 列打印的行前面有一个制表符。

`comm` 实用程序假设文件已按词法排序；所有字符都参与行比较。

## 环境变量

`LANG`、`LC_ALL`、`LC_COLLATE` 和 `LC_CTYPE` 环境变量会影响 `comm` 的执行，如 [environ(7)](https://github.com/FreeBSD-Ask/freebsd-man-sc/blob/main/man7/environ.7.md) 所述。

## 退出状态

`comm` 实用程序成功时退出值为 0，发生错误时大于 0。

## 实例

假设有一个名为 `example.txt` 的文件，内容如下：

```sh
a
b
c
d
```

显示仅在 `example.txt` 中的行、仅在标准输入中的行以及共同的行：

```sh
$ echo -e "B\nc" | comm example.txt -
        B
a
b
                c
d
```

仅显示共同行，进行不区分大小写的比较：

```sh
$ echo -e "B\nc" | comm -1 -2 -i example.txt -
b
c
```

## 参见

[cmp(1)](/man/man1/cmp.1.md), [diff(1)](https://github.com/FreeBSD-Ask/freebsd-man-sc/blob/main/man1/diff.1.md), [sort(1)](https://github.com/FreeBSD-Ask/freebsd-man-sc/blob/main/man1/sort.1.md), [uniq(1)](https://github.com/FreeBSD-Ask/freebsd-man-sc/blob/main/man1/uniq.1.md)

## 标准

`comm` 实用程序符合 ISO/IEC 9945-2:1993 ("POSIX.2") 规范。

`-i` 选项是对 POSIX 标准的扩展。

## 历史

`comm` 命令首次出现于 Version 4 AT\&T UNIX。


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