A shell colon does nothing. Use it anyway
1–10 of 191 posts
Re: A shell colon does nothing. Use it anyway
#2I am not a huge fan of most of these, but a few do seem useful.
: "${1:?missing argument, aborting!}"
Many of the others (like truncating files) are probably more clearly written with dedicated commands, but may come in useful if you are going to extreme lengths to avoid dependencies outside of the shell.
Re: A shell colon does nothing. Use it anyway
#3the truncation is a poor example.
- it creates the file if it does not exist, not merely truncate. as a tutorial kind of blog post this incomplete description matters IMO.
- it would work the same without the colon (similar for default variable assignment examples). we generally strive not to have "extra" things, like useless use of cat.
- educationally it's useful to demonstrate that redirection, like parameter expansion, works before the command executes (the null command in this case), but the article doesn't explain that at all!
otherwise i <3 this article. some uses of colon i had never thought of or seen before. like file truncation, not sure i'd use them but it was cool to see them.
Re: A shell colon does nothing. Use it anyway
#4life is way too short to deal with this nightmare of a language and its 50000 footguns for anything longer than a 2 line script, especially in the age of LLMs. Just write a python/TS/any real language script instead. Bash is great for the command line, it should be limited to use there.
Re: A shell colon does nothing. Use it anyway
#5life is way too short to deal with this nightmare of a language and its 50000 footguns for anything longer than a 2 line script, especially in the age of LLMs. Just write a python/TS/any real language script instead. Bash is great for the command line, it should be limited to use there.
It turns out that LLMs are really good at writing bash too. even perl! maybe we should rethink some of these lost bits because we no longer need to worry about the arcane parts.
Re: A shell colon does nothing. Use it anyway
#6I am not a huge fan of most of these, but a few do seem useful. : "${1:?missing argument, aborting!}" I wouldn't use this because I would want to give $1 a name for the rest of the script, so I would assign. But it can be a nice way to give a clear error for missing required environment variables. Many of the others (like truncating files) are probably more clearly written with dedicated commands, but may come in use…
Yo, author here.
You are very much correct and I 100% agree with you, I have updated the first example to include a snippet where a proper env-var is used to show of the automatic diagnostic.
Thanks for your feedback, much much appreciated!
Re: A shell colon does nothing. Use it anyway
#7I am not a huge fan of most of these, but a few do seem useful. : "${1:?missing argument, aborting!}" I wouldn't use this because I would want to give $1 a name for the rest of the script, so I would assign. But it can be a nice way to give a clear error for missing required environment variables. Many of the others (like truncating files) are probably more clearly written with dedicated commands, but may come in use…
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Re: A shell colon does nothing. Use it anyway
#8Prefer
if x then :; else something; fi
if ! x; then something; fi
Re: A shell colon does nothing. Use it anyway
#9I am not a huge fan of most of these, but a few do seem useful. : "${1:?missing argument, aborting!}" I wouldn't use this because I would want to give $1 a name for the rest of the script, so I would assign. But it can be a nice way to give a clear error for missing required environment variables. Many of the others (like truncating files) are probably more clearly written with dedicated commands, but may come in use…
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Re: A shell colon does nothing. Use it anyway
#10the truncation is a poor example. - it creates the file if it does not exist, not merely truncate. as a tutorial kind of blog post this incomplete description matters IMO. - it would work the same without the colon (similar for default variable assignment examples). we generally strive not to have "extra" things, like useless use of cat. - educationally it's useful to demonstrate that redirection, like parameter expa…
Hey jiveturkey, author here!
I agree with you, and for what it's worth the truncation snippet is very much tongue-in-cheek much like `( : >> output ) && echo "is writable"`.
I wasn't expecting anyone to actually use these in Prod, rather I aimed to show what can be done with a command designed to.. do nothing (crazy).
Happy you enjoyed the article, and thank you!