Arguments, quotes and file checks

Articles

• bash — the command shell — A command interpreter for interactive input, builtins, and shell scripts.
• Bash scripts: running, variables, arguments — A script is a text file of shell commands: the #! line picks the interpreter, arguments arrive in $1, $2 and "$@".
• Exit codes: $?, && and || — An exit code is a number from 0 to 255 that a command reports: 0 means success, anything else a failure or a "no".
• test, [ ] and [[ ]] — checking conditions — test and [ ] check a file, a string or a number and answer with a code: 0 is yes, 1 is no; [[ ]] is the bash version.
• Output redirection and pipelines — A shell instruction that connects a command's stream to a file or another descriptor: > overwrites a file, >> appends, < reads from a file, and 2>&1 sends stderr wherever stdout goes.