https://learn-bash.net/ Free Bash and shell tutorials, plus how to write scripts and agent hooks that fail safely. Sun, 06 Sep 2026 03:07:12 GMT https://learn-bash.net/hello-world/https://learn-bash.net/hello-world/The tutorial discusses shell programming in general with focus on Bash (“Bourne Again Shell”) shell as the main shell interpreter. https://learn-bash.net/ai/hooks-and-guardrails/https://learn-bash.net/ai/hooks-and-guardrails/Your agent runs more shell than anything else, and shell is the one place a mistake is not recoverable. Here is how to write the scripts that keep it honest. https://learn-bash.net/review/failure-modes/https://learn-bash.net/review/failure-modes/Generated shell is usually correct on the happy path and dangerous on every other one. Almost all of it is caught by one tool. https://learn-bash.net/variables/https://learn-bash.net/variables/Shell variables are created once they are assigned a value. A variable can contain a number, a character or a string of characters. https://learn-bash.net/passing-arguments-to-the-script/https://learn-bash.net/passing-arguments-to-the-script/Arguments can be passed to the script when it is executed, by writing them as a space-delimited list following the script file name. https://learn-bash.net/review/dependencies/https://learn-bash.net/review/dependencies/A shell script's dependencies are every external command it calls, every flag it assumes, and every installer it pipes into a shell. None of that is declared anywhere. https://learn-bash.net/ai/agents-md/https://learn-bash.net/ai/agents-md/The shortest useful instructions file on this network — four lines of script header, a shellcheck rule, and one sentence about when to stop writing shell at all. https://learn-bash.net/arrays/https://learn-bash.net/arrays/An array can hold several values under one name. Array naming is the same as variables naming. https://learn-bash.net/review/security/https://learn-bash.net/review/security/Shell has no sandbox, no type system and no undo. Every variable is a potential injection point and every script runs with your full privileges. https://learn-bash.net/ai/tokenomics/https://learn-bash.net/ai/tokenomics/Your agent already writes a complete record of every session to disk. Twenty lines of shell turns it into a spend report, and one hook keeps it honest. https://learn-bash.net/basic-operators/https://learn-bash.net/basic-operators/Arithmetic Operators Simple arithmetics on variables can be done using the arithmetic expression: $((expression)) The basic operators are: a + b addition (a plus b) a - b substraction (a minus b) a b multiplication (a times b) a / b division (integer) (a divided by b) a % b modulo (the integer remainder of a divided by b) a b exponentiation (a to the power of b) https://learn-bash.net/review/performance/https://learn-bash.net/review/performance/Shell performance is almost entirely about how many processes you start. Generated scripts start a great many, and the fix is usually to delete code rather than add it. https://learn-bash.net/basic-string-operations/https://learn-bash.net/basic-string-operations/The shell allows some common string operations which can be very useful for script writing. https://learn-bash.net/decision-making/https://learn-bash.net/decision-making/As in popular programming languages, the shell also supports logical decision making. https://learn-bash.net/loops/https://learn-bash.net/loops/For each pass through the loop, arg takes on the value of each successive value in the list. Then the command(s) are executed. https://learn-bash.net/array-comparison/https://learn-bash.net/array-comparison/Comparison of arrays Shell can handle arrays An array is a variable containing multiple values. Any variable may be used as an array. https://learn-bash.net/shell-functions/https://learn-bash.net/shell-functions/Like other programming languages, the shell may have functions. A function is a subroutine that implements a set of commands and operations. https://learn-bash.net/case-statements/https://learn-bash.net/case-statements/Pattern matching on a string — cleaner than a chain of if/elif, and the backbone of every argument parser and dispatch table in shell. https://learn-bash.net/special-variables/https://learn-bash.net/special-variables/In last tutorial about shell function, you use “$1” represent the first argument passed to functionA. https://learn-bash.net/bash-trap-command/https://learn-bash.net/bash-trap-command/It often comes the situations that you want to catch a special signal/interruption/user input in your script to prevent the unpredictables. https://learn-bash.net/input-parameter-parsing/https://learn-bash.net/input-parameter-parsing/Turning $@ into a usable set of options: manual loops, getopts, long flags, and the --dry-run habit that makes a script safe to run once. https://learn-bash.net/file-testing/https://learn-bash.net/file-testing/Often you will want to do some file tests on the file system you are running. In this case, shell will provide you with several useful commands to achieve it. https://learn-bash.net/pipelines/https://learn-bash.net/pipelines/Pipelines, often called pipes, is a way to chain commands and connect output from one command to the input of the next. https://learn-bash.net/process-substitution/https://learn-bash.net/process-substitution/In the previous section we’ve seen how to chain output of one command to the next one. https://learn-bash.net/regular-expressions/https://learn-bash.net/regular-expressions/Bash has a regex operator built in, and it is better than piping to grep for most jobs — once you know the two quoting rules that trip everyone up. https://learn-bash.net/special-commands-sed-awk-grep-sort/https://learn-bash.net/special-commands-sed-awk-grep-sort/The four tools that do most of the work in most shell scripts, and the small subset of each that is worth memorising. https://learn-bash.net/here-documents-and-redirection/https://learn-bash.net/here-documents-and-redirection/Where output goes, where input comes from, and how to embed a block of text in a script without fighting quotes.