In Python, how to get the epoch time (the number of seconds since epoch)? In Python, you can get the epoch time by calling time.time() which return a floating number: import time print time.time() If you would like to get only the number of seconds, you may convert it to an integer. One example is…
In Python, how to get the value (string) of an environment variable? In Python, all environment variables can be accessed directly through os.environ import os print os.environ[‘HOME’] If the environment variable is not present, it will raise a KeyError. You can use get to return None if the environment variable is not present: print os.environ.get(‘ENV_MIGHT_EXIST’)…
In Bash, how to get the value (string) of an environment variable? In Bash, just directly use: $VAR Note that if you assigned a value to the “local” variable $VAR in your program before reading the “environmental” $VAR, the $VAR will actually contain the value you assigned.
In Bash, how to process a file line by line? The file is a plain text line like input.txt. As an example, the process can be to just print it out. In Bash to process a file ./input.txt line by line: while read line ; do echo $line done < ./input.txt Reference: https://www.systutorials.com/qa/2166/how-to-process-a-file-line-by-line-in-go
sort supports –parallel N to run N thread. However, it seems it only uses around 100% CPU as I observed although the command specified that N threads can be used. The command is as follows cat large-file | sort –parallel `nproc` where I have 16 from nproc. How to make sort use multiple threads to…
In PHP, how to process a file line by line? The file is a plain text line like input.txt. As an example, the process can be to just print it out. In PHP, you can use this code snippet to process a file line by line: if ( ($fhandle = fopen(“./input.txt”, “r”) !== FALSE )…
In C++, how to process a file line by line? The file is a plain text line like input.txt. As an example, the process can be to just print it out. In C++, you may open a input stream on the file and use the std::getline() function from the <string> to read content line by…
Any good suggestions on a Java REPL implementation like ‘scala’ and ‘python’ or ‘php -a’? The java-repl tool https://github.com/albertlatacz/java-repl/ works nicely for most situations for me. It is released as a .jar. Hence, it is easy to download and run: $ wget –quiet https://github.com/albertlatacz/java-repl/releases/download/428/javarepl-428.jar -O /tmp/javarepo-428.jar && java -jar /tmp/javarepo-428.jar One usage example is as…
How to convert a svg image file to a high-quality png file in Linux? inkscape works great with vector images (better than ImageMagikk’s convert). Try this command to convert in.svg to a 1000×1000 png image: inkscape -z -e out.png -w 1000 -h 1000 in.svg
Go lang is fast to compile and can be used as a script by go run prog.go. However, a REPL is more convenient for testing/trying some small pieces of code. Any good Go REPL implementation / tool? Try gore https://github.com/motemen/gore Get gore $ go get -u github.com/motemen/gore An example $ gore gore version 0.2.6 :help…
In Python, how to get hostname as the command hostname does on Linux? In Python, you can get the hostname by the socket.gethostname() library function in the socket module: import socket hostname = socket.gethostname() Reference: https://www.systutorials.com/dtivl/20/how-to-get-the-hostname-of-the-node?show=34#a34
In Python, how to process read a file line by line to process it? Like those lines in Bash: while read line ; do echo $line done < ./input.txt In Python, you can process a file line by line by a for in the file like with open(“./input.txt”, “r”) as thefile: for line in thefile:…
I got this error when I tried to save a file with a space in its name into HDFS: $ hdfs dfs -put -f “/home/u1/testa/test a” “/u1/testa/test a” put: unexpected URISyntaxException while the HDFS seems allow spaces in its file names: https://hadoop.apache.org/docs/r2.7.3/hadoop-project-dist/hadoop-common/filesystem/model.html . How to achieve the effect of saving the files with spaces in…
In Python, how to get an environment variable? In Python, you may use this piece of code to get an environment variable: os.environ.get(‘ENV_MIGHT_EXIST’) or this piece of code: os.getenv(‘ENV_MIGHT_EXIST’) It will return None if the environment variable is not present. Reference and for more ways, please check https://www.systutorials.com/dtivl/13/how-to-get-an-environment-variable?show=80#answer-80 .
In Go lang, how to get an environment variable? To get an environment variable (e.g. “VAR”) in GO: import “os” import “fmt” fmt.Println(“VAR:”, os.Getenv(“VAR”))
How to convert a byte[] to io.Reader in Go directly? You can use the NewReader() func from the bytes package of Go to convert bytes to io.Reader. For example, reader := bytes.NewReader(thebytes)
i need to create a program which is taking information from printer , so that i cannot use os namespace , so there is any way without using the os namespace You may use a way as follows. open the file seek to the end tell its position which is the file size An example…
Not yet to totally delete the Linux user account, but how to effectively disable a Linux user account? That is, disable a user account while keep all its files/configurations. Later, if it is needed, so that I can enable it again. To effectively disable a Linux user account so that it can’t login using its…
In system, sometimes, we need backstage threads with very very low priority since it cannot preempt any normal process asks for CPU. SCHED_IDLE class satisfies this requirement which has the priority lower than “nice=19” of CFS. Following code does this. 241 void set_idle_priority(void) { 242 struct sched_param param; 243 param.sched_priority = 0; 244 int s…
We may need to check some materials about how to do good research in system field if you a Ph.D. focusing on system research. Some references: 1, How to write a good systems paper 2, How to be a good graduate student 3, Doing a System Ph.D. 4, Giving an Academic Talk Welcome to add…