大部分功能强大的文本编辑器都提供重新格式化段落的命令;供用户切分段落,使文本行数不要超出我们看到的屏幕范围.这样我们就引入了 fmt 命令,虽然一些 fmt 的实现有较多的选项可用,但其实只用:-s 仅切割较长的行,但不会将短行结合成较长的行,而-w n 则设置输出行宽度为 n 个字符(默认通常是 75 个).
fmt 命令的语法:
fmt [option] [file-list]
fmt 通过将所有非空白的长度设置为几乎相同,来进行简单的文本格式化.
-s 截断长行，但不合并
-t 除每个段落的第 1 行外都缩进
-u 改变格式化，使字之间出现一个空格，句子之间出现两个空格
-w n 将输出的行宽改为 n 个字符。不带该选项时，fmt 输出的行宽度为 75 个字符
例如,我有一个文件 demo,内容为:
A long time ago, there was a huge apple tree. A little boy loved to come and play around it every day. He climbed to the tree top, ate the apples, took a nap under the shadow… He loved the tree and the tree loved to play with him.
使用命令 fmt -s demo,输出为:
A long time ago, there was a huge apple tree. A little boy loved
to come and play around it every day. He climbed to the tree top, ate
the apples, took a nap under the shadow… He loved the tree and the
tree loved to play with him.
该命令的含义是节段2长行.
使用fmt -t demo命令的意思是说排除首行的缩进,结果为:
A long time ago, there was a huge apple tree. A little boy loved
to come and play around it every day. He climbed to the tree top,
ate the apples, took a nap under the shadow… He loved the tree and
the tree loved to play with him.
使用fmt -u demo命令的意思是说格式化单词和句子的间隔.输出为:
A long time ago, there was a huge apple tree. A little boy loved to come
and play around it every day. He climbed to the tree top, ate the apples,
took a nap under the shadow… He loved the tree and the tree loved to
play with him.
显然 A little boy 前面的多个空格变成了两个.
使用命令fmt -w 40 demo意思是说指定行的宽度,这里的行宽为 40 个字符.所以输出为:
A long time ago, there was a huge
apple tree. A little boy
loved to come and play around it
every day. He climbed to the tree top,
ate the apples, took a nap under the
shadow… He loved the tree and the
tree loved to play with him.
仅作切割的选项： -s , 在你想将长的行绕回，短的行保持不动时很好用，这么做也能使结果与原始版本间的差异达到最小,例如:
fmt -s -w 10 << EOF
one two three four five
six
seven
eight 输出为:
one two
three
four five
six
seven
eight
fmt 的小案例:
下面以拼音字典为例：
字典文件：/usr/dict/words 或者/usr/share/dict/words。
sed -n -e 9991,10010p /usr/share/dict/words | fmt
sed -n -e 9991,10010p /usr/share/dict/words | fmt -w 30
观察上面两行命令的输出.
复习一下 sed 命令:
sed 是一个很好的文件处理工具，本身是一个管道命令，主要是以行为单位进行处理，可以将数据行进行替换、删除、新增、选取等特定工作.假设我们有一个文件 demo
sed ‘1d’ demo 删除第一行
sed -n ‘1p’ 显示第一行
sed -n ‘/root/p’ demo 查询包括关键字 root 所在所有行
sed ‘1a hahaha’ demo 第一行后增加字符串 hahaha
sed ‘1,3a hahaha’ demo 第一行到第三行后增加字符串 hahaha
sed ‘1c hihihi’ demo 第一行代替为 hihihi
sed ‘1,2c hihihi’ demo 第一行和第二行替换为 hihihi
替换一行中的某部分
格式：sed 's/要替换的字符串/新的字符串/g' （要替换的字符串可以用正则表达式）,案例:
sed ‘s/root/hahaha/g’ 替换 root 为 hahaha
sed ‘s/root//g’ 删除 root
sed -i '$a bye' ab #在文件ab中最后一行直接输入"bye"