Bash中printf和echo的区别 [英] Difference between printf and echo in Bash

问题描述

$ printf 'apple' | wc -m
       5
$ echo 'apple' | wc -m
       6

为什么printf可打印5个字符，而echo则可打印6个字符?

Why printf prints 5 and echo prints 6 characters?

推荐答案

bash手册页(重点是我的内容)中echo的第一句话:

First sentence of entry for echo in the bash man page (emphasis mine):

输出以空格分隔的args，后跟换行符.

printf手册页条目的第一句:

First sentence of the man page entry for printf:

在格式的控制下将格式化的参数写入标准输出.

Write the formatted arguments to the standard output under the control of the format.

printf仅打印格式显示的内容；它不会附加隐含的换行符.

printf only prints what appears in the format; it does not append an implied newline.

echo "foo"和printf "foo"之间可能还有其他差异，具体取决于foo的确切含义. POSIX规范在如何实现echo方面为实现提供了广泛的自由裁量权，可能是避免从各种历史实现中选择一种作为标准.依靠精确的输出时，请使用printf.

There may be other difference between echo "foo" and printf "foo", depending on what exactly foo is. The POSIX specification gives implementations broad discretion in how it implements echo, probably to avoid choosing from among the diverse historical implementations as the standard. Use printf when you rely on the precise output.

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