shell基础之基本命令

                shell 基本命令分析 <一>

 

1. echo

synopsis

    echo [SHORT-OPTION]... [STRING]...

    echo LONG-OPTION

 

作用：echo the string(s) to standard output

常用option:

-n   取消行末换行符

-e   启用反斜线控制字符的转换   (如: \t, \n, \r, \b)

-E   关闭反斜线控制字符的转换

$ echo first line
first line
$ echo -n first line
first line $

$ echo -e "a\tb\tc\nd\te\tf"
a    b    c
d    e    f

 

2. tr

synopsis

   tr [OPTION] ... SET1 [SET2]

description

   translate, squeeze, and/or delete characters from standard input, writing to standard output.

tr用来从标准输入中通过替换或删除操作进行字符转换。主要用于删除文件中控制字符或进行字符转换。使用tr时要转换两个字符串：字符串1用于查询，字符串2用于处理各种转换。
tr刚执行时，字符串1中的字符被映射到字符串2中的字符，然后转换操作开始.

带有最常用选项的tr命令格式为：

tr -c -d -s ["string1_to_translate_from"] ["string2_to_translate_to"] inputfile

-c 用字符串1中字符集的补集替换此字符集，要求字符集为ASCII。
-d 删除字符串1中所有输入字符。
-s 删除所有重复出现字符序列，只保留第一个；即将重复出现字符串压缩为一个字符串。

去除重复出现的字符

$ cat sample.txt
thisss is a sammmpllleee.

 

$tr -s [a-z] < sample.txt
this is a sample.

or

$cat sample.txt | tr -s [a-z]
this is a sample.

删除空行

$cat space.txt
first line


second line

 

$cat space.txt | tr -s "[\n]"
first line
second line

大写到小写
除了删除控制字符,转换大小写是tr最常用的功能.为此需指定即将转换的小写字符[a-z]和转换结果[A-Z].

$echo "first second." | tr [a-z] [A-Z]
FIRST SECOND.

也可以使用字符类[:lower:]和[:upper:] 

$echo "first second" | tr [:lower:] [:upper:]
FIRST SECOND

删除指定字符

$cat char.txt
one 123
two 2345
three 345622

输出保留字符，不要数字

$tr -cs "[a-z][A-Z]" "[\n*]" < char.txt
one
two
three

转换控制字符

unix中打开来自dos的文件时，会遇到如下格式的文本.

$cat -v dos.txt
this file from dos^M
I want to change it^M
^Z

使用-s 选项将^M,^Z转换成回车符.查ASCII表，^M是015，^Z是032.

$tr -s "[\015\032]" "\n" < dos.txt > unix.txt
$cat -v unix.txt
this file from dos
I want to change it

将所有Tab换空行：  tab 011, space 040

$tr -s "[\011]" "[\040*]" < tabtos.txt

[character*n]格式匹配多于一个字符

 

3. cut   - remove sections from each line of files

cut OPTION... [FILE]...

-d, --delimiter=DELEM

-f, --fields=LIST

eg: uname -r | cut -d. -f1,2

result: $2.6

4. install  - copy files and set attributes

  install [OPTION]... [-T] SOURCE DEST

 *install [OPTION]... SOURCE... DIRECTORY

  install [OPTION]... -t DIRECTORY SOURCE...

  install [OPTION]... -d DIRECTORY...

OPTION:

-[cC]  -b  -[dD]  -[tT] -p -m ...

-d, --directory

eg:     $install -d ex{1..5}     <==>  mkdir ex{1..5}

-D  create all leading components of DEST except the last, then copy SOURCE to DEST

-m, --mode=MODE 

    set permission mode (as in chmod), instead of rwxr-xr-x

-p, --preserve-timestamps  保留原文件的访问修改时间

    apply access/modification times of SOURCE files to orresponding     destination files

eg: $install -p -m 644 sample /usr/bin

-o, --owner=OWNER
    set ownership (super-user only)
-s, --strip
    strip symbol tables

-S, --suffix=SUFFIX
    override the usual backup suffix

-t, --target-directory=DIRECTORY
    copy all SOURCE arguments into DIRECTORY

-T, --no-target-directory
    treat DEST as a normal file

-g, --group=GROUP
    set group ownership, instead of process' current group