为什么在标准输入上对文件进行 gzip 压缩会产生比作为参数给出的同一文件更小的输出？

Question

因为它会保存文件名和时间戳，以便稍后解压缩后可以尝试恢复它们。由于在第二个示例中foo给出了gzipvia <stdin>，因此它无法存储文件名和时间戳信息。

从联机帮助页：

   -n --no-name
          When compressing, do not save the original file name and time stamp by default. (The original name is always saved if the name had
          to  be truncated.) When decompressing, do not restore the original file name if present (remove only the gzip suffix from the com-
          pressed file name) and do not restore the original time stamp if present (copy it from the compressed file). This  option  is  the
          default when decompressing.

   -N --name
          When compressing, always save the original file name and time stamp; this is the default. When decompressing, restore the original
          file name and time stamp if present. This option is useful on systems which have a limit on file name  length  or  when  the  time
          stamp has been lost after a file transfer.

我在这里重现了这个问题：

[root@xxx601 ~]# cat /etc/fstab > file.txt
[root@xxx601 ~]# gzip < file.txt > file.txt.gz
[root@xxx601 ~]# gzip -c file.txt > file2.txt.gz
[root@xxx601 ~]# ll -h file*
-rw-r--r--. 1 root root  465 May 17 19:35 file2.txt.gz
-rw-r--r--. 1 root root 1.2K May 17 19:34 file.txt
-rw-r--r--. 1 root root  456 May 17 19:34 file.txt.gz

在我的示例中，file.txt.gz相当于您的foo2.gz.使用该-n选项会禁用此行为，否则会可以访问以下信息：

[root@xxx601 ~]# gzip -nc file.txt > file3.txt.gz
[root@xxx601 ~]# ll -h file*
-rw-r--r--. 1 root root  465 May 17 19:35 file2.txt.gz
-rw-r--r--. 1 root root  456 May 17 19:43 file3.txt.gz
-rw-r--r--. 1 root root 1.2K May 17 19:34 file.txt
-rw-r--r--. 1 root root  456 May 17 19:34 file.txt.gz

file.txt正如您在上面看到的，和的文件大小file3.txt匹配，因为它们现在都省略了名称和日期。

Answer 1