fold 命令
fold 命令用于限制文件列宽。
fold 指令会从指定的文件里读取内容，将超过限定列宽的列加入增列字符后，输出到标准输出设备。若不指定任何文件名称，或是所给予的文件名为"-"，则 fold 指令会从标准输入设备读取数据。
语法
fold [-bs][-w<每列行数>][--help][--version][文件...]
选项：
- -b 或--bytes 以 Byte 为单位计算列宽，而非采用行数编号为单位。
- -s 或--spaces 以空格字符作为换列点。
- -w<每列行数>或--width<每列行数> 设置每列的最大行数。
- --help 在线帮助。
- --version 显示版本信息。
实例
将一个名为 testfile 的文件的行折叠成宽度为 30，可使用如下命令：
fold -w 30 testfile
为了对比，先将 testfile 文件输出如下：
$ cat testfile #查看testfile 中的内容
Linux networks are becoming more and more common, but
security is often an overlooked
issue. Unfortunately, in today’s environment all networks
are potential hacker targets,
from top-secret military research networks to small home LANs.
Linux Network Security focuses on securing Linux in a
networked environment, where the
security of the entire network needs to be considered
rather than just isolated machines.
It uses a mix of theory and practical techniques to
teach administrators how to install and
use security applications, as well as how the
applications work and why they are necessary.
然后使用 fold 命令折叠显示：
$ fold -w 30 testfile #行折叠成宽度为30，显示testfile 文件
Linux networks are becoming mo
re and more common, but securi
ty is often an overlooked issu
e. Unfortunately, in today’s
environment all networks are
potential hacker targets, from
top-secret military research
networks to small home LANs.
Linux Network Security focuses
on securing Linux in a networ
ked environment, where the sec
urity of the entire network ne
eds to be considered rather th
an just isolated machines. It
uses a mix of theory and pract
ical techniques to teach admin
istrators how to install and u
se security applications, as w
ell as how the applications wo
rk and why they are necessary