I try to do as little shell scripting as I can get away with. But I thought
I’d put a little set of notes together for my own reference. My bias here
tends toward trying to minimize clutter, so I have a better shot at actually
seeing what’s going on.
DO use [[ ]] in conditions, so > is greater (not redirect) and $X is “$X”
As far as I can tell, basically any if statement should use the double
bracket form.
http://mywiki.wooledge.org/BashFAQ/031
DON’T put variable values in quotes that don’t need it (FOO=x not FOO=”x”)
Bash’s medium is strings, and it’s willing to delimit those strings for you
implicitly when they don’t have spaces. Might as well use that.
DO put variable substitutions in quotes (“$X” not $X), EXCEPT in [[ ]]
Seeing [[ ]] as a whole separate universe seems to be the way to go. So I
figure why not take advantage of the feature of the implicit quoting.
https://unix.stackexchange.com/q/131766/
DON’T use curly braces on variables unless needed (“$FOO” not “${FOO}”)
The $ calls enough attention to the fact that it’s a variable. So if you
aren’t splicing a variable into a place where it abuts other characters that
would be mistaken as part of the variable name, avoid the {}.
https://unix.stackexchange.com/a/4910
DO use = in [[ ]] conditions for lexical comparison (= not ==)
https://unix.stackexchange.com/a/16110
DON’T put space between x=y when doing variable assignments
A good reason not to do this is because you can’t! :-/
https://unix.stackexchange.com/a/297217
DON’T use superfluous semicolons at end of lines of shell commands
https://stackoverflow.com/a/7507242/
DO use $(...) vs. `...` for shell execution
To me, it just seems more obvious that the $ means “substitute”. But also,
I kind of like special-purposing `...` for calling out code in comments.
(Plus, as I write this, backticks are a pain to escape in MarkDown. Best if
you just leave them out of your code.)
https://stackoverflow.com/a/9406350/
“$foo 123” -> substitutes foo contents to get foocontents 123
This one I tend to remember.
‘$foo 123’ -> takes it literally, so you get $foo 123
This one I forget about.
xargs may be a useful command when dealing with the shell
Something to look at:
http://man7.org/linux/man-pages/man1/xargs.1.html (e.g. ... | xargs cat)
