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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• echo <text> prints the specified text on standard output
  • evaluation of metacharacters (special characters) inside the text may be performed first
    
  • -e says to enable interpretation conversion of backslash escapes such as \t (Tab) and \n newline to their ASCII character
    
  • -n says not to output the trailing newline
• wc -l  reports the number of lines (-l) in its input
  
  • wc -c reports the number of characters (-c) in its input
    
  • wc -w reports the number of words (-w) in its input
• history lists your command history to the terminal
  • redirect to a file to save a history of the commands executed in a shell session
  • pipe to grep to search for a particular command
    
• which <pgm> searches all $PATH directories to find the program/command <pgm> and reports its full pathname
• du <file_or_directory><file_or_directory>..
  
  • shows the disk usage (size) of the specified files/directories
  • -h says report the size in human-readable form (e.g. 12M instead of 12201749)
  • -s says summarize the directory size for directories
  • -c says print a grand total when multiple items are specified
• seq N generates a set of N numbers, 1 through N
• groups - lists the Unix groups you belong to

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• Default field separators
  • Tab is the default field separator for cut
  • whitespace (one or more spaces or Tabs) is the default field separator for awk
• Re-ordering
  • cut cannot re-order fields
  • awk can re-order fields, based on the order you specify
• awk is a full-featured programming language while cut is just a single-purpose utility.

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grep and regular expressions

• grep -P '<pattern>' searches for <pattern> in its input, and only outputs lines containing it
  • always enclose '<pattern>' in single quotes to inhibit shell evaluation!
    • pattern-matching metacharacters in grep are very different from those in the shell
  • -P says to use Perl patterns, which are much more powerful (and standard) than default grep patterns
  • -v (inverse match) – only print lines with no match
  • -n (line number) – prefix output with the line number of the match
  • -i  (case insensitive) – ignore case when matching
  • -l says return only the names of files that do contain the pattern match
  • -L says return only the names of files that do not contain the pattern match
  • -c says just return a count of line matches
  • -A <n> (After) and -B <n> (Before) – output <n> number of lines after or before a match

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