How to delete or get the number in the tail from a string in shell script (bash script)? Okay to call other tools. For example, from “/dev/sda8”, I want to get “/dev/sda” and “8” separately. This can be achieved by using sed as follows. To get the string after deleting the tailing numbers, we can…
In Go lang, how to get the hostname of the node? In Go, you can use the os.Hostname() function to get the hostname of the node. func Hostname() (name string, err error) Hostname returns the host name reported by the kernel. One example is as follows. The main.go source code: package main import ( “fmt”…
In C, how to get the hostname of the node? In C, you may use the gethostname function. #include <unistd.h> int gethostname(char *name, size_t namelen); The gethostname() function shall return the standard host name for the current machine. The namelen argument shall specify the size of the array pointed to by the name argument. The…
In C++, how to get the hostname of the node? In C++, the C way works too. However, with Boost, you can use the boost::asio::ip::host_name() function to get the hostname as a std::string: namespace boost { namespace asio { namespace ip { /// Get the current host name. BOOST_ASIO_DECL std::string host_name(); … More at http://www.boost.org/doc/libs/1_63_0/boost/asio/ip/host_name.hpp…
In Bash, how to convert an epoch timestamp to a human readable date format? In Bash, you can use the date command’s -d option: date -d @<your epoch> Here @ specifies the epoch timestamp. One example: $ date -d @1490157520.05 Wed Mar 22 12:38:40 HKT 2017
Getting the hostname of the node running a program can be useful in various scenarios, such as creating logs with the hostname, identifying which node a script is running on, or configuring a distributed system with different nodes. In Bash, there are several ways to retrieve the hostname of the machine, as mentioned in the…
In Python, how to get the hostname of the node? In Python, you can get the hostname by the socket.gethostname() library function in the socket module: import socket hostname = socket.gethostname() Example: $ python Python 2.7.5 (default, Nov 6 2016, 00:28:07) [GCC 4.8.5 20150623 (Red Hat 4.8.5-11)] on linux2 Type “help”, “copyright”, “credits” or “license”…
In C, how to get the epoch timestamp, the number of seconds passed since the epoch? In C, from man 7 time: UNIX systems represent time in seconds since the Epoch, 1970-01-01 00:00:00 +0000 (UTC). A program can determine the calendar time using gettimeofday(2), which returns time (in seconds and microseconds) that have elapsed since…
How to convert an epoch timestamp to a human readable date format? In Python: import time time.strftime(“%a, %d %b %Y %H:%M:%S %Z”, time.localtime(epoch)) One example: $ python Python 2.7.5 (default, Nov 6 2016, 00:28:07) [GCC 4.8.5 20150623 (Red Hat 4.8.5-11)] on linux2 Type “help”, “copyright”, “credits” or “license” for more information. >>> import time >>>…
In Java, how to get the epoch timestamp, the number of seconds passed since the epoch? In Java, you can get the current time in milliseconds and then calculate the epoch time: long ts = System.currentTimeMillis()/1000; Example: $ 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 Welcome to JavaREPL version 428 (Java HotSpot(TM) 64-Bit…
In Go lang, how to get the epoch timestamp, the number of seconds passed since the epoch? In Go, you can use the time.Now() func to get current time and its Unix() func to convert it into an epoch timestamp: import(“time”) func getEpochTime() int64 { return time.Now().Unix() } If you would convert a time string…
In PHP, how to get the epoch timestamp, the number of seconds passed since the epoch? In PHP, you can use the time() function. ts = time(); To get the microsecond together too as a float number, use the microtime(true) function. ts2 = microtime(true); Example: $ php -a Interactive shell php > echo time() ….
In Perl, how to get the epoch timestamp, the number of seconds passed since the epoch? In Perl, to get the epoch time, call the time function: my $ts = time Example: $ perl -e ‘print time . “n”‘ 1491473202
In Java, how to get the value (string) of an environment variable? You may call the System.getenv(name) library function in Java to get the environment variable value. public static String getenv(String name) Parameters: name – the name of the environment variable Returns: the string value of the variable, or null if the variable is not…
In Bash, how to get the epoch timestamp, the number of seconds passed since the epoch? In Bash, you can call the date command with format option “+%s”: date +%s Here, “%s” means: %s seconds since 1970-01-01 00:00:00 UTC
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 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 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 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…