How to check if there are only spaces in a string?
I want to use conditions in an if() statement.
For example,
str<-" "< br />#check if str has only white spaces? example usage
i
Category: OS
Operating System (Operating System, referred to as OS) is a computer program that manages and controls computer hardware and software resources. It is the most basic system software that runs directly on the “bare metal”. Any other software must be supported by the operating system to run .
Signal capture trap and its usage in shell
kll -l command to view all signals
Some of the most commonly used signal values are as follows
#! /bin/bash
trap’echo “good”‘ 2 Here you can use numeric numbers, signal names or abbreviations
sleep 100 When the above script is running, if We a
Regular expression – parts matching with EGREP regular expression
I want to know, if I use egrep ((GNU grep)2.5.1), I can select a part of the matching text, for example:
grep’^([a-zA-Z.-]+)[0-9]+’ ./file.txt So I only get the matching part between th
Regular expression – What is the best way to make a string operation in a shell script?
I have a path as a string in a shell script, which can be absolute or relative:
/usr/userName/config.cfg< /p> or
../config.cfg
I want to extract the file name (the part after the
Shell script printing and other waist triangles
Shell script printing isosceles triangle #!/bin/bash
for ((i=1;i<= 9;i++))
do
for ((j=9;j>=i;j- -))
do
echo -n ” ”
done
for ((j=2;j<= i;j++)) do echo -n "*" done for ((j=1
Shell – interactive input
Interactive input and for statement (8-15)
Interactive input
1, read Usage: The read command can define multiple variable values at the same time, and the input content can be used as
Shell script prints the right angle triangle
The shell script prints a right-angled triangle #! /bin/ bash
for ((i=1;i<= 9;i++)) do for ((j=1;j<=$i;j++ )) do echo -n "*" done echo done
#! /bin/bash
for ((i=1;i<= 9;i++)) do for ((j=1;j<=$i;j++ )) do echo -n "*" done echo done
DHCP Server – Dynamic Host Configuration Protocol
The main configuration file: /etc/dhcp/dhcpd.conf is almost empty
Reference template: /usr/share/doc/dhcp-4.2.5/dhcpd.conf .sample
IP information and related lease information: /var/lib/dhcpd/dhcpd
Regular expression – Why does this frontal assertion does not work when anchored to the beginning of a string?
Why does this post-assertion not work when it is fixed at the front of the string? Run the following code, and you will see that the first test passes, but the second test only passes the ^ anchor
Bash – Extract many pre-guides from a huge text file
I have a huge text file. I want to extract the first 532541 lines of it and store them in another file. Selecting the text with the mouse and executing ctrl c is obviously not a feasible Solution.<