Linux Learning-standard input and output

standard input and output redirection-- any command executed under Linux will go through the process shown:

Directory

1. Three types of I/O devices

2. Redirect I/O to a file

3. Tr

4. Using the Pipe link command

5. Practical cases

I. I/O devices

• Three types of I/O devices are available in Linux:

Standard input (STDIN)-0 accepts input from the keyboard by default

Standard output (STDOUT)-1 Default output to terminal window

Standard error (STDERR)-2 default output to terminal window

• Operation Symbols:

1> or > correct output to file

2> error Output to file

> cover

2>> Append

file exists:> and >> can create new file

file does not exist:> overwrite >> append

set-c is forbidden, but can be appended

>|+ file name Force Overwrite

Set +c Allow overwrite

&> All output Files

2>&1 Turn the wrong into the right

1>&2 Turn the right into the wrong

() merging output from multiple programs

Example: (Cal 2007;cal) > All.text

• TR Conversion characters

For example:

tr ABCD 123 converts a conversion of A to 1,b to 2,CD to 3

TR ABC 1234 converts a to 1,b converted to 2,c to 3, 4 invalid

tr-t ABCD 123 will a->1,b->2,c->3,d invalid

tr-d A removes the A string

echo Hello 123 World | tr-cd 0-9 only leaves the 0-9, Deleting all characters in the input text that are not in the complement (a bit around) /c16>

Run results

tr-s ab converts multiple consecutive A and b into a and B

TR A [:p UNCT:] will error

• < input redirection

tr-d Abd </etc/fstab Delete any of the ABC characters in the Fstab file

cat > File then enter the content, Ctrl+d left in a disguised form of an input

cat > File3.txt </etc/fstab Copy the contents of Fstab to File3.txt

Video 56.03 screenshot

• << Termination Words ****** is used in scripts ******

cat > File4.txt << EOF

Video Screen 57.19 screenshot

• | piping  -- Pass the correct result of the front output to the next command to execute

can take advantage 2>&1 | error results can also be passed to the pipeline

Less paging to view output

ls-l/etc |

mail-s "subject" + username --e-mail sent to the specified user

User Lisi send the subject as test, the content is Hello World mail to the user Zhanshan, the result diagram is as follows:

Combined with pipe breaks:

echo Hello World | mail-s "Test" +username

• Case:

1. Convert the contents of the/etc/issue file to uppercase and save to the/tmp/issue.out file

cat/etc/issue |tr A-z >/tmp/issue.out

TR A-Z </etc/issue >/tmp/issue.out

2. Convert the current system login user's information to uppercase and save to the/tmp/who.out file

W.H.O. | tr [A-z] [a-z] >/tmp/who.out

3, a Linux user to the root email, request the message titled "Help", the message body is as follows:

Hello, I am Username, the system version is Here,please help me to Check it, thanks+ operating system version information

ECHO-E hello,i am ' whoami ', the system version is Here,please help me to check it,thanks. " \ n "' Cat/etc/redhat-release ' | Mail-s Help Root

4, the/root/file list, displayed as a line, and the file name separated by a space

Ls-1/root/|tr "\ n" ""

5. Calculation 1+2+3+. The sum of +99+100

echo {1..100} |tr "" + |BC

6, processing string "Xt.,l 1 jr#! $mn 2 c*/fe 3 uz 4", keep only the numbers and Spaces

echo "Xt.,l 1 jr#hat-releasemn 2 c*/fe 3 uz 4" | TR-CD [:d Igit:][:blank:]

7. Display the path variable in a separate row for each directory

echo $PATH |tr: "\ n"

Linux Learning-standard input and output