Bash from the ground up

Learn the shell by writing it: printing and quoting, exit codes, decisions with if and case, loops, functions, arrays, arithmetic, and the pipelines of small text tools that shell work is really made of — ending with a capstone report that builds its own data and filters it.

What You'll Learn

• Run a script, and print with echo and with printf
• Keep values in variables, and know what quoting does to them
• Read exit codes, and join commands with && and ||
• Branch with if, test numbers, text and files, and match patterns
• Choose between several possibilities with case
• Repeat work with for, while and a range of numbers
• Write functions that take arguments and answer with text or a code
• Hold a list in an array, and loop over it without splitting it
• Do arithmetic with whole numbers, and know where the fraction goes
• Filter text with grep, sort, uniq, cut, head, tr and wc
• Capture command output in a variable, and edit text with sed and awk
• Build a data file, filter it with a pipeline and print a summary

Prerequisites

• No programming experience needed — this course starts at a script file
• A terminal you have typed a command or two into makes the first chapters quicker

Course Content

1. 01
   Your first script

   What a shell script is, how to print a line with echo and with printf, and why those two commands do not always agree about a backslash.

   Beginner · 14 min read

   Not started
2. 02
   Values in variables, and quoting

   Naming a value, the strict rule about spaces around the equals sign, and the everyday difference between "$name" and a pair of single quotes.

   Beginner · 16 min read

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3. 03
   Exit codes and joining commands

   Every command answers with a number, $? holds the last one, and && and || let you decide what runs next without writing an if at all.

   Beginner · 15 min read

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4. 04
   Decisions with if

   Branching on a test: if, else and elif, the test brackets, the different spellings for numbers and for text, and the safer double-bracket form.

   Beginner · 18 min read

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5. 05
   Matching with case

   One value, several patterns, and a branch for each: how case replaces a ladder of tests, and why its patterns are not quite the tests you already know.

   Intermediate · 14 min read

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6. 06
   Loops that repeat work

   Three ways to repeat: for over a list of words, while with a counter, and the brace range that writes a run of numbers for you.

   Intermediate · 18 min read

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7. 07
   Functions and their arguments

   Naming a block of lines, passing values in as $1 and $2, collecting them with "$@", and the two ways a function can hand an answer back.

   Intermediate · 20 min read

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8. 08
   Arrays of values

   One name for a list of values: reading items by their position, counting them, adding one, and the quoting that keeps each item whole.

   Intermediate · 16 min read

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9. 09
   Arithmetic in the shell

   Working with numbers: the double round brackets, the everyday operators, and the one rule that surprises everybody — the shell counts in whole numbers only.

   Advanced · 15 min read

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10. 10
    Pipelines and text tools

    The vertical bar that hands one command output to the next, and the seven small tools that most shell work is built from.

    Advanced · 20 min read

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11. 11
    Captured output, sed and awk

    Keeping what a command printed in a variable, and the two tools you reach for when a line of text needs changing or reshaping.

    Advanced · 20 min read

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12. 12
    Putting it together: a log report

    A capstone that uses the whole course once: build a data file, filter it with a pipeline, keep the answers in variables, and print a summary that lines up.

    Advanced · 22 min read

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