Page Comparison

This page should serve as a reference for the many "things Linux" we use in this course. It is by no means complete – Linux is **huge** – but offers introductions to many important topics.

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• Macs and Linux have a Terminal program built-in
• Windows options:
  • Windows 10+
    • Command Prompt and PowerShell programs have ssh and scp (may require latest Windows updates)
      • Start menu → Search for Command
    • Putty – http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html
      
      • simple Terminal and file copy programs
      • download either the Putty installer or just putty.exe (Terminal) and pscp.exe (secure copy client)
    • Windows Subsystem for Linux – Windows 10 Professional includes a Ubuntu-like bash shells
      • See https://docs.microsoft.com/en-us/windows/wsl/install-win10
      • We recommend the Ubuntu Linux distribution, but any Linux distribution will have an SSH client

Use ssh (secure shell) to login to a remote computers.

# General form:
ssh <user_name>@<full_host_name>

# For example
ssh abattenh@ls6.tacc.utexas.edu

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• Right arrow and Left arrow move the cursor forward or backward on the current command line.
• Use Ctrl-a (holding down the Control key and a) to jump the cursor to the beginning start of the line.
• Use Ctrl-e to jump the cursor to the end of the line.
• Arrow keys are also modified by Ctrl- (Windows) or Option- (Mac)
  
  • Ctrl-right-arrow (Windows) or Option-right-arrow (Mac) will skip by "word" forward
  • Ctrl-left-arrow (Windows) or Option-left-arrow (Mac) will skip by "word" backward

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This text will be output
And this USER environment variable will be evaluated: student01

Arithemetic in bash

Arithmetic in bash is very weird:

echo $(( 50 * 2 + 1 ))

n=0
n=$(( $n + 5 ))
echo $n

And it only returns integer values, after truncation.

echo $(( 4 / 2 ))
echo $(( 5 / 2 ))

echo $(( 24 / 5 ))

As a result, if I need to do anything other than the simplest arithemetic, I use awk:

awk 'BEGIN{print 4/2}'
echo 3 2 | awk '{print ($1+$2)/2}'

You can also use the printf function in awk to control formatting. Just remember that a linefeed ( \n ) has to included in the format string:

echo 3.1415926 | awk '{ printf("%.2f\n", $1) }'

You can even use it to convert a decimal number to hexadecimal using the %x printf format specifier. Note that the convention is to denote hexadecimal numbers with an initial 0x.

echo 65 | awk '{ printf("0x%x\n", $1) }'

Bash control flow

the bash for loop

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