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This article mainly introduces shell how to remove the blank lines in the document, has a certain reference value, interested friends can refer to, I hope you can learn a lot after reading this article, the following let the editor take you to understand it.

This section contains:

Shell removes blank lines from the file

1the shell removes the blank lines from the file.

The code is as follows:

Cat filename | sed-e'/ ^ $/ d'> filename

2. Keep the latest 9 files and delete the other files.

The code is as follows:

Ls-t | awk'{if (NR > 9) {print $0}}'| xargs rm-f

Attached, special variables in shell

$

PID (ProcessID) of Shell itself

$!

The PID of the background Process that the Shell last ran

$?

The end code of the last run command (return value)

$-

Flag list set using the Set command

$*

List of all parameters. In the case of "$*" enclosed by "$", with "$1 $2". Outputs all parameters in the form of $n ".

$@

List of all parameters. In the case of "$@" surrounded by ", output all parameters in the form of" $1 "" $2 "…" $n ".

$#

Number of parameters added to Shell

, 0

The file name of the Shell itself

$1 million

The parameter values added to the Shell. $1 is the first parameter, $2 is the second parameter.

Judge test

Whether test-f is a file or not

-d whether it is in the directory or not

Does the-e file exist?

Man test

Judge 7 file types

Test-f $1 & & cat $1 ordinary file

Test-d $1 & & ls-ld $1 directory

Test-L $1 & & ls-ld $1 connection file

Test-p $1 & & ls-ld $1 pipe file

Test-S $1 & & ls-ld $1 socket

Test-b $1 & & ls-ld $1 device

Test-c $1 & & ls-ld $1 character device

Here are a few examples for your reference.

1, compare the size of numbers

The code is as follows:

#! / bin/bash

Test $1-gt $2 & & echo $1

Test $1-lt $2 & & echo $2

Test $1-eq $2 & & echo $1 thanks 2

2, judge the string

The code is as follows:

#! / bin/bash

Test $1! = $2 & & echo is not equal

Test $1 / 2 & & echo $1 / 2

3, combination judgment

1),

The code is as follows:

#! / bin/bash

Test $1-gt 5-a $1-lt 10 & & echo $1

If

#! / bin/bash

If test $1-gt 5 (or if [$1-gt 5] Note spaces)

Then

Echo $1

Fi

2),

The code is as follows:

#! / bin/bash

Ping-c 1-W 1 192.168.0.room1 & > / dev/null (- c 1 means ping once,-W target host unreachable timeout is 1 second)

If [$?-eq 0]

Then

Echo link OK

Esle

Echo link no

Fi

SHELL deletes blank lines or blank lines in the file:

Today, I found that there are too many blank lines in a file. I intend to delete the blank lines in it.

So use sed, check the command, and write:

Sed'/ ^ $/ d'file1

It is inexplicable to find that there are still a lot of blank lines in the output.

So: sed'/ ^ $/ p 'file1 finds that there are very few blank lines in the output, but there are actually a lot of blank lines.

So use cat-A file1

Only to find that there are space characters in many lines, so that the regular does not recognize that it is a blank line.

So change it to: sed'/ ^ * $/ d 'file1. Now it's OK.

Also note that the newline character under windows is ^ M $.

Under LINUX, it is $. If it is a file under WINDOWS, it needs to be converted. Using doc2unix seems to be this tool.

Linux shell deletes the file blank line three:

The log file to be viewed recently has a lot of blank lines after extraction, which is not conducive to the comparison of previous files. In order to be compatible with each other, the blank lines can only be deleted. Their own google for a while, using the grep method, the efficiency is still very fast, 25000 + lines of 73 blank lines, instant fix, should be able to take over.

Method 1: (this is what I use)

Grep-v "^ $" file removes matching blank lines

In addition, when troubleshooting and finding errors, we also use grep to check which lines are blank lines, so as to see why those lines do not have this information from the original log file.

Add the parameter-n grep-n "^ $" file to find the blank line and go to the original log file to view the information.

Method 2: use the tr command

Cat file name | tr-s'\ n'

Method 3: use the sed command

Cat file name | sed'/ ^ $/ d'

Method 4: use the awk command

Cat file name | awk'{if ($0,000,") print}'

Cat file name | awk'{if (length! = 0) print $0}'

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