Category: Programming

Variabel di Shell Script

In the previous issue we’ve become acquainted with a shell script and managed to create a very simple shell script. If we look, we did not perform any processing on the shell script. We only show a message on the screen and execute commands on the shell through shell script. What if we want to make the program more interactive shell script?

As with any programming language, shell script also serves to recognize the variables that can hold information temporarily for a variety of purposes, for example to compute or determine the output results. You may make as much as possible or use a variable in your shell script. Name the variables are independent, large and small letters should, but make it easier to remember, make it a habit to create standard rules in the manufacture of the variable name. At this writing, all variables will be written in lowercase.

Variables can be divided into two types, namely environment variables and user variables. Environment variables are variables that have been previously determined as a part of the shell used (bash). By default, the name of this variable using all capital letters. Example of this is the $ USER variable that will contain the user name you are currently using, $ HOME home directory which contains the address of the user that is used, and so forth. To display the entire value of an existing environment variable, you can use the set command in the terminal (Figure 1). User variable is the variable name specified by the user themselves and not by the shell used.

Variables can be accessed by using the dollar sign ($) before the variable name, for example, we have a variable named “my name”, to access the value stored in the variable, we use the $ my name. To give value to a variable, we use the sign “=” is immediately followed by the value we give without any spaces, for example my name = Willy. What if the value that we want to give is a sentence? Use double quotes as the opening and closing value of a variable, such as my name = “Willy Sudiarto Raharjo”. For example, see listing 1 and try running on your computer. Seen that the value of the variable Sudiarto be regarded as a command and not part of the variable because it is not enclosed in double quotation marks. Please be careful in giving a value to a variable.

You can combine environment variables and user variables in a shell script is the same, as in listing 2. What if want to write a message using the $ character, such as “It cost me $ 15”? If we are not careful, it could be a shell script would be wrong to interpret the information that we provide and try to take the value of variable 1 (which will not contain any) and display it as a “price 5”. To fix this, use the escape character to indicate that the next character will be recognized as a regular character and not as a substitute for a variable, which marks the backslash “\” as in listing 3.

One character that needs more attention is the backtick character “` “(position number 1 on the left side your keyboard) because this character has a special function in shell programming, which is able to accommodate the output of a shell command in a variable. As an example, we will hold the result of the date command into a variable date and display its contents using the echo command as in listing 4.

To be able to receive input from the user and store it into a variable, we can use the read function is followed by the name of the variable that we want to use to store the values ​​as in Example 5 listings.

Seven signs of dysfunctional engineering teams

I’ve been listening to the audiobook of Heart of Darkness this week, read by Kenneth Branagh. It’s fantastic. It also reminds me of some jobs I’ve had in the past.

There’s a great passage in which Marlow requires rivets to repair a ship, but finds that none are available. This, in spite of the fact that the camp he left further upriver is drowning in them. That felt familiar. There’s also a famous passage involving a French warship that’s blindly firing its cannons into the jungles of Africa in hopes of hitting a native camp situated within. I’ve had that job as well. Hopefully I can help you avoid getting yourself into those situations.

There are several really good lists of common traits seen in well-functioning engineering organizations. Most recently, there’s Pamela Fox’s list of What to look for in a software engineering culture. More famous, but somewhat dated at this point, is Joel Spolsky’s Joel Test. I want to talk about signs of teams that you should avoid.

This list is partially inspired by Ralph Peters’ Spotting the Losers: Seven Signs of Non-Competitive States. Of course, such a list is useless if you can’t apply it at the crucial point, when you’re interviewing. I’ve tried to include questions to ask and clues to look for that reveal dysfunction that is deeply baked into an engineering culture.

Preference for process over tools. As engineering teams grow, there are many approaches to coordinating people’s work. Most of them are some combination of process and tools. Git is a tool that enables multiple people to work on the same code base efficiently (most of the time). A team may also design a process around Git — avoiding the use of remote branches, only pushing code that’s ready to deploy to the master branch, or requiring people to use local branches for all of their development. Healthy teams generally try to address their scaling problems with tools, not additional process. Processes are hard to turn into habits, hard to teach to new team members, and often evolve too slowly to keep pace with changing circumstances. Ask your interviewers what their release cycle is like. Ask them how many standing meetings they attend. Look at the company’s job listings, are they hiring a scrum master?

Excessive deference to the leader or worse, founder. Does the group rely on one person to make all of the decisions? Are people afraid to change code the founder wrote? Has the company seen a lot of turnover among the engineering leader’s direct reports? Ask your interviewers how often the company’s coding conventions change. Ask them how much code in the code base has never been rewritten. Ask them what the process is for proposing a change to the technology stack. I have a friend who worked at a growing company where nobody was allowed to introduce coding conventions or libraries that the founding VP of Engineering didn’t understand, even though he hardly wrote any code any more.

Unwillingness to confront technical debt. Do you want to walk into a situation where the team struggles to make progress because they’re coding around all of the hacks they haven’t had time to address? Worse, does the team see you as the person who’s going to clean up all of the messes they’ve been leaving behind? You need to find out whether the team cares about building a sustainable code base. Ask the team how they manage their backlog of bugs. Ask them to tell you about something they’d love to automate if they had time. Is it something that any sensible person would have automated years ago? That’s a bad sign.

Not invented this week syndrome. We talk a lot about “not invented here” syndrome and how it affects the competitiveness of companies. I also worry about companies that lurch from one new technology to the next. Teams should make deliberate decisions about their stack, with an eye on the long term. More importantly, any such decisions should be made in a collaborative fashion, with both developer productivity and operability in mind. Finding out about this is easy. Everybody loves to talk about the latest thing they’re working with.

Disinterest in sustaining a Just Culture. What’s Just Culture? This post by my colleague John Allspaw on blameless post mortems describes it pretty well. Maybe you want to work at a company where people get fired on the spot for screwing up, or yelled at when things go wrong, but I don’t. How do you find out whether a company is like that? Ask about recent outages and gauge whether the person you ask is willing to talk about them openly. Do the people you talk to seem ashamed of their mistakes?

Monoculture. Diversity counts. Gender diversity is really important, but it’s not the only kind of diversity that matters. There’s ethnic diversity, there’s age diversity, and there’s simply the matter of people acting differently, or dressing differently. How homogenous is the group you’ve met? Do they all remind you of you? That’s almost certainly a serious danger sign. You may think it sounds like fun to work with a group of people who you’d happily have as roommates, but monocultures do a great job of masking other types of dysfunction.

Lack of a service-oriented mindset. The biggest professional mistakes I ever made were the result of failing to see that my job was ultimately to serve other people. I was obsessed with building what I thought was great software, and failed to see that what I should have been doing was paying attention to what other people needed from me in order to succeed in their jobs. You can almost never fail when you look for opportunities to be of service and avail yourself of them. Be on the lookout for companies where people get ahead by looking out for themselves. Don’t take those jobs.

There are a lot of ways that a team’s culture can be screwed up, but those are my top seven.

Acquainted with BASH Scripting

It is undeniable that over time, the popularity of Linux is increasing every day. Linux Kernel project which was originally just a fun project by Linux apparently transformed into a project that became the basis for the evolution of the digital world today.

We can see that more and more digital devices are therein using Linux in it. Changes were made in all areas so that Linux can be used by all users, both from the ground level up to the experts though.

One thing that remains a hallmark of Linux is the existence of a shell that is never lost on any Linux distro. Shell is a command-line interpreter on duty to translate the commands entered by the user directly to the system through the help of a terminal or console as a zoom interface (such as Command Prompt on the Windows platform). Although today most of the Linux distributions already to offering graphical display, the shell is still regarded as one of the strengths of Linux shell bridge where users can interact with the system in order to be more flexible. Many things can be done on a shell because we are dealing directly with the system, coupled with the many variants of the shell that offers a variety of features in it, such as csh, sh, bash, ksh, tcsh, ash, zsh, etc.

One of the most common type of shell used is BASH (Bourne-Again Shell) which was created by Bryan Fox in 1988. Shell is a replacement of the Bourne Shell (sh) existing first and is still used in some Linux distributions. Currently BASH shell has become a de facto standard for almost all Linux distributions because it is considered the most feature-rich and has a fairly high degree of portability. For comparison between variants shell can be seen on the Wikipedia website

To be able to understand the Linux system with better and also improve your productivity and take advantage of the flexibility offered by Linux, so it’s good we are trying to learn programming BASH script. PCplus using Slackware Linux distro, but this tutorial can be applied to all Linux distributions for use BASH version 4.2 and above. You can use any text editor because basically BASH script is plain text file. You can also try it on a Windows platform with the help of Cygwin,

open the editor:

1. The first step in creating a shell script is telling the system what shell you want to use, because it could be available in a Linux distribution over the shell variant. Because we want to use bash, then write this line in the first row of each bash shell script that will be created

This code is called the shebang and a special instruction that will determine what the interpreter is going to be used to process a shell script. For example, for a script that utilizes Perl interpreter, it will contain information

2. Because the shell script is basically able to execute commands on the shell, then we can run shell commands from a shell script. For example, we want to display today’s date along with the name that we use username to login. Use the code on the listing-1 as an example. Before you can run the script, give it execute permissions on the file with the command chmod + x’s listing (adjust the file name you gave) then run the command.

Date command displays the current date information while whoami will menapilkan your user information to login.

3. What if we want to display the text coupled with a shell command? Use the echo function to display a message to the screen shown in listing-2. Echo function accepts parameters in the form of a text message that will be displayed kelayar. You might ask, why the date and user information are on different lines with text displayed? This is due essentially echo function will display a message and then change the next line. To be able to display an information to the right of the text is displayed, use the-n parameter on the function like echo in the listing-3.

4. You can try some of the commands contained in the location / bin and / usr / bin. If not sure of the usefulness of a command, run the command man <nama-perintah> on the console or terminal, for example, man ls and manual information about the ls command will be displayed. Each command has a variation of different parameters with each other, so there are times when we have to read the manual to know every option available.