Re: Long variable value get corrupted sometimes

[Daniel Qian]

Thanks for your tips, a lot learned.

Greg Wooledge <greg@wooledge.org> 于2022年2月16日周三 20:47写道：

>
> On Wed, Feb 16, 2022 at 04:10:40PM +0800, Daniel Qian wrote:
> > FOO=$(cat /tmp/foo.txt)
> > got_md5=$(echo "$FOO" | md5sum -b | cut -d ' ' -f 1)
>
> In addition to what other people have said... echo is not reliable.  It
> may alter your text, if you feed it backslashes, or arguments like "-e"
> or "-n".
>
> text=$(cat /tmp/foo.txt)                    # this strips all trailing 
> newlines
> md5=$(printf '%s\n' "$text" | md5sum -b)    # this adds one newline
> md5=${md5%% *}                              # this removes " *-"
>
> If you need to preserve the correct number of trailing newlines, then
> you'll also have to change the command substitution.  The common
> workaround is:
>
> text=$(cat /tmp/foo.txt; printf x)
> text=${text%x}
>
> If you do this, remember that the final newline(s) are still inside the
> variable, so you don't need to add one:
>
> md5=$(printf %s "$text" | md5sum -b)
>
> Finally, you should get in the habit of NOT using all-caps variable
> names for regular shell variables.  The all-caps namespace is "reserved"
> for environment variables (like HOME and PATH) and special shell variables
> (like BASH_VERSION and SECONDS).
>
> Ordinary variables that you use in a script should contain lowercase
> letters.  Mixed caps/lowercase is fine, if you swing that way.
>


--
Daniel Qian
Apache Committer(chanjarster)
blog：https://chanjarster.github.io
github：https://github.com/chanjarster
segmentfault: https://segmentfault.com/u/chanjarster