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Lesson 3

These final exercises will cover some commands useful for development, operational purposes and the elegance of piping.

Before concluding we'll demystify command history and get a taste of some advanced shortcuts.

Exercises

  1. Simple file readers: less is more
    • Slightly more versatile versions of cat that contain simple text searches
    • less hello_grep.txt
    • Type / to enter search mode & then hello as your search string and hit enter
    • the up/down arrow keys and space (page down) will aid in page navigation
    • sometimes less is not available on containers but more is
    • more hello_grep.txt
  2. Display parts of a file: head and tail
    • Both commands give you a sample of a large flat file and tail is the workhorse of log watching
    • head hello_grep.txt prints the first 10 lines (default) of a file
    • head -3 hello_grep.txt prints the first 3 lines of a file
    • tail -5 hello_grep.txt prints the last 5 lines of a file (default is also 10)
  3. The original computer-search noun that became a verb (no, not google) grep:

    • Simple & flexible command to locate text in a flat file

    • grep hello hello_grep.txt

    • Aside from simple searches grep also fully supports regular expressions

    • grep can also be used to ignore certain text grep -v hello hello_grep.txt

    • By default, grep is case-sensitive but ignoring case is also common grep -i hello hello_grep.txt

    • fun fact, grep stands for "Globally search for a Regular Expression and Print matching lines"

    • Example GIF

      CopyAndRemove

  4. Simple web request tool: curl
    • curl comes in handy when testing out APIs or doing an investigation for front end work
    • It's light weight but also capable enough all varieties of HTTP requests
    • Get your ip address curl ifconfig.me
    • Check the headers for debugging curl -v ifconfig.me
    • Sample POST request curl 'https://jsonplaceholder.typicode.com/posts' --data-raw '{"title":"foo","body":"bar","userId":1}' -H 'content-type: application/json; charset=UTF-8'
    • Your favorite web browser can export curl commands from the network tab of the developer console
  5. Putting it all together with pipe |

    • One of the most elegant features of shell programming is ability to easily tie multiple commands together using the pipe | operator.

    • Developers who created the early shell commands weren't focused on solving every possible use case for their tools but rather kept them simple for the purpose of efficiency & speed.

    • To allow for flexibility the | utility allowed users to stitch together various commands to accomplish their unique use case.

    • Specifically, a command on the left side of | feeds its output directly to the input of the command on the right side

    • tail hello_grep.txt | grep hello

    • grep hello hello_grep.txt | grep twist

    • Execute the given script to create a simulated log file: ./log_generator.sh & (note: the & sends the script execution to the background)

    • tail -f grep.log

    • press ctrl+c to stop following the file

    • tail -f grep.log | grep hello

    • press ctrl+c to stop following the file

    • Check the content type of a HTTP response curl -s -I ifconfig.me | grep content-type

    • Example GIF

      CopyAndRemove

  6. Command history
    • history will display a list of your previous commands in descending order
    • Using the up/down arrow keys at shell prompt traverses this history
    • It can be combined w/ pipe to find that nifty command you used yesterday history | grep curl
    • There's an even better way!
  7. Basic shell keyboard shortcuts:
    • The best shortcut has already been covered tab for completion.
    • shortcut ctrl + r is used to recursively look up your previous history. Once prompted type characters and simple regex will be used to locate the previous command that matches it. Type ctrl + r again to locate the next oldest match
    • ctrl + c will kill whatever program you are running and is also handy to delete your current prompt
    • ctrl + l will clear your shell (mac also supports cmd + k)
    • ctrl + d is a shortcut to exit the current session (note: this will close your current tab)
  8. If you forget use the manual: man
    • Anytime you forget how to use a command know that there are manuals for them all
    • man curl
    • It can be meta! man man

References: