大部分功能強(qiáng)大的文本編輯器都提供重新格式化段落的命令；供用戶(hù)切分段落，使文本行數(shù)不要超出我們看到的屏幕范圍。這樣我們就引入了 fmt 命令，雖然一些 fmt 的實(shí)現(xiàn)有較多的選項(xiàng)可用，但其實(shí)只用:-s 僅切割較長(zhǎng)的行，但不會(huì)將短行結(jié)合成較長(zhǎng)的行，而 -w n 則設(shè)置輸出行寬度為 n 個(gè)字符 (默認(rèn)通常是 75 個(gè))。

fmt 命令的語(yǔ)法:

fmt [option] [file-list]

fmt 通過(guò)將所有非空白的長(zhǎng)度設(shè)置為幾乎相同，來(lái)進(jìn)行簡(jiǎn)單的文本格式化。

-s 截?cái)嚅L(zhǎng)行，但不合并
-t 除每個(gè)段落的第 1 行外都縮進(jìn)
-u 改變格式化，使字之間出現(xiàn)一個(gè)空格，句子之間出現(xiàn)兩個(gè)空格
-w n 將輸出的行寬改為 n 個(gè)字符。不帶該選項(xiàng)時(shí)，fmt 輸出的行寬度為 75 個(gè)字符

例如，我有一個(gè)文件 demo，內(nèi)容為:

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，輸出為:

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.

該命令的含義是節(jié)段 2 長(zhǎng)行。

使用 fmt -t demo 命令的意思是說(shuō)排除首行的縮進(jìn)，結(jié)果為:

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 命令的意思是說(shuō)格式化單詞和句子的間隔。輸出為:

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.

顯然 A little boy 前面的多個(gè)空格變成了兩個(gè)。

使用命令 fmt -w 40 demo 意思是說(shuō)指定行的寬度，這里的行寬為 40 個(gè)字符。所以輸出為:

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.

僅作切割的選項(xiàng)： -s，在你想將長(zhǎng)的行繞回，短的行保持不動(dòng)時(shí)很好用，這么做也能使結(jié)果與原始版本間的差異達(dá)到最小，例如:

fmt -s -w 10 << EOF
one two three four five
six
seven
eight
輸出為:
one two
three
four five
six
seven
eight

fmt 的小案例:

下面以拼音字典為例：

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

觀察上面兩行命令的輸出。

復(fù)習(xí)一下 sed 命令:

sed 是一個(gè)很好的文件處理工具，本身是一個(gè)管道命令，主要是以行為單位進(jìn)行處理，可以將數(shù)據(jù)行進(jìn)行替換、刪除、新增、選取等特定工作。假設(shè)我們有一個(gè)文件 demo

sed '1d' demo    刪除第一行
sed -n '1p' 顯示第一行
sed -n '/root/p' demo 查詢(xún)包括關(guān)鍵字 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  第一行代替為 hihihi
sed '1,2c hihihi' demo  第一行和第二行替換為 hihihi

替換一行中的某部分

格式：sed 's/ 要替換的字符串 / 新的字符串 /g'   （要替換的字符串可以用正則表達(dá)式），案例:
sed 's/root/hahaha/g'  替換 root 為 hahaha
sed 's/root//g' 刪除 root 
sed -i '$a bye' ab         #在文件 ab 中最后一行直接輸入 "bye"

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