Shell Scripting

Notes on shell scripting, as well as some zsh- and bash-specific stuff.

Notes

  • zsh has two representations for array variables like PATH and CDPATH, of which the lower case variant is an actual array

  • ~ is a special character. Therefore, if you use it in a string variable and then try to do something with it, ~ will be evaluated literally, and not expanded to the value of $HOME. So use $HOME in these cases instead

  • Functions can be declared with/without function keyword and parens

    • my_function (), function my_function, etc

  • To pass arguments to a function, just use spaces

    • my_function "hello" "world"

    • If passing variables, sometimes it's good practice to put them in quotes in case the variables have spaces in them

  • The export keyword is only necessary when sub-processes need access to the variable

    • So if you don't use export, when you execute programs they won't have access to the variable. But the resulting shell will

  • To do string transformation on strings in zsh upon expansion, use expansion flags

  • To rename the current directory: mv ../current_dir ../new_dir_name or mv ../{test,test2} (uses brace expansion for brevity)

  • Assigning test/[[]] results to a variable (tl;dr: there's not a great way to do this). This would be nice for code readability

  • Can't assign variable to command exit status directly

  • macOS has a weird quirk where filenames with a : show a / for them instead

    • Can get around this if you need to by using this guy instead: ꞉ -- it's a different character but looks pretty similar

  • For conditionals, 0 is truthy and 1 is falsey

  • For multline string usage, use HereDoc

  • For stripping trailing characters, use parameter expansion %: ${var%/}, (stripping /)

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