linux基础知识-I/O重定向,管道

Posted 2020-08-31

系统设定
 默认输出设备：标准输出，STDOUT, 1
 默认输入设备：标准输入, STDIN, 0
 标准错误输出：STDERR, 2
 
标准输入：键盘
标准输出和错误输出：显示器

I/O重定向：

Linux:
>: 覆盖输出

[[email protected] ~]# ll /var/ > /tmp/var.out
[[email protected] ~]# cat /tmp/var.out
total 76
drwxr-xr-x.  2 root root 4096 Jun 21  2015 account
drwxr-xr-x. 13 root root 4096 Jun 21  2015 cache
drwxr-xr-x.  2 root root 4096 Jun 21  2015 crash
drwxr-xr-x.  3 root root 4096 Jun 21  2015 db
drwxr-xr-x.  3 root root 4096 Jun 21  2015 empty
drwxr-xr-x.  2 root root 4096 Jun 28  2011 games

#
# /etc/fstab
# Created by anaconda on Sun Jun 21 02:15:00 2015
#
# Accessible filesystems, by reference, are maintained under ‘/dev/disk‘
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
UUID=57d85756-7680-4c7c-9125-6ad67dae2c45 /                       ext4    defaults        1 1
UUID=2622a4b4-ddc9-47a3-aa2b-f06bc9bec085 /boot                   ext4    defaults        1 2
UUID=33d94759-fa01-4c4f-b4ac-bf3a1fe5e84f swap                    swap    defaults        0 0
tmpfs                   /dev/shm                tmpfs   defaults        0 0
devpts                  /dev/pts                devpts  gid=5,mode=620  0 0
sysfs                   /sys                    sysfs   defaults        0 0
proc                    /proc                   proc    defaults        0 0

>>：追加输出

2>: 重定向错误输出

[[email protected] ~]# ls /varr > /tmp/var2.out
ls: cannot access /varr: No such file or directory
[[email protected] ~]# ls /varr 2> /tmp/var2.out
[[email protected] ~]# cat /tmp/var2.out
ls: cannot access /varr: No such file or directory
[[email protected] ~]#
2>>: 追加方式

&>: 重定向标准输出或错误输出至同一个文件

[[email protected] ~]# ls /var6 &> /tmp/var3.out
[[email protected] ~]# cat /tmp/var3.out
ls: cannot access /var6: No such file or directory
[[email protected] ~]# ls /var &> /tmp/var3.out
[[email protected] ~]# cat /tmp/var3.out
account
cache
crash
db
empty

---

输入重定向

<：输入重定向

[[email protected] ~]# tr ‘a-z‘ ‘A-Z‘ < /etc/fstab

#
# /ETC/FSTAB
# CREATED BY ANACONDA ON SUN JUN 21 02:15:00 2015
#
# ACCESSIBLE FILESYSTEMS, BY REFERENCE, ARE MAINTAINED UNDER ‘/DEV/DISK‘
# SEE MAN PAGES FSTAB(5), FINDFS(8), MOUNT(8) AND/OR BLKID(8) FOR MORE INFO
#
UUID=57D85756-7680-4C7C-9125-6AD67DAE2C45 /                       EXT4    DEFAULTS        1 1
UUID=2622A4B4-DDC9-47A3-AA2B-F06BC9BEC085 /BOOT                   EXT4    DEFAULTS        1 2
UUID=33D94759-FA01-4C4F-B4AC-BF3A1FE5E84F SWAP                    SWAP    DEFAULTS        0 0
TMPFS                   /DEV/SHM                TMPFS   DEFAULTS        0 0
DEVPTS                  /DEV/PTS                DEVPTS  GID=5,MODE=620  0 0
SYSFS                   /SYS                    SYSFS   DEFAULTS        0 0
PROC                    /PROC                   PROC    DEFAULTS        0 0
[[email protected] ~]#

<<：此处是文档

[[email protected] ~]# cat << END
> the first line
> the second line
> END
the first line
the second line
[[email protected] ~]#

从键盘中读入数据，并保存在文档中

cat >> /tmp/myfile.txt << EOF

[[email protected] ~]# cat >> /tmp/myfile.txt << EOF
> the first line
> the second line
> EOF
[[email protected] ~]# cat /tmp/myfile.txt
the first line
the second line
[[email protected] ~]#

---

管道：前一个命令的输出，作为后一个命令的输入

命令1 | 命令2 | 命令3 | ...

[[email protected] ~]# echo "hello,world" | tr ‘a-z‘ ‘A-Z‘
HELLO,WORLD
[[email protected] ~]#

[[email protected] ~]# echo "redhat" | passwd --stdin hive
Changing password for user hive.
passwd: all authentication tokens updated successfully.
[[email protected] ~]#

同时输出到屏幕和文件中

[[email protected] ~]# echo "hello,world" | tee /tmp/hello.out
hello,world
[[email protected] ~]# cat /tmp/hello.out
hello,world
[[email protected] ~]#

统计文件行数

[[email protected] ~]# wc -l /etc/passwd
32 /etc/passwd
[[email protected] ~]# wc -l /etc/passwd | cut -d‘ ‘ -f1
32
[[email protected] ~]#

---

练习：
1、统计/usr/bin/目录下的文件个数；
# ls /usr/bin | wc -l
2、取出当前系统上所有用户的shell，要求，每种shell只显示一次，并且按顺序进行显示；
# cut -d: -f7 /etc/passwd | sort -u
3、思考：如何显示/var/log目录下每个文件的内容类型？

4、取出/etc/inittab文件的第6行；
# head -6 /etc/inittab | tail -1
5、取出/etc/passwd文件中倒数第9个用户的用户名和shell，显示到屏幕上并将其保存至/tmp/users文件中；
# tail -9 /etc/passwd | head -1 | cut -d: -f1,7 | tee /tmp/users
6、显示/etc目录下所有以pa开头的文件，并统计其个数；
# ls -d /etc/pa* | wc -l
7、不使用文本编辑器，将alias cls=clear一行内容添加至当前用户的.bashrc文件中；
# echo "alias cls=clear" >> ~/.bashrc