Why can't I redirect output to file path beginning with a tilde (~)?

Question

I am a long time bash user, but ran into something I have never seen before (or simply don't remember). I was getting a "No such file or directory" error when trying to redirect output to a log file, something I have done thousands of times but evidently not quite in this manner. Here is a sample output that recreates the problem:

test.sh:

#!/bin/bash
logfile="~/logs/$(date +%Y%m%d_%H%M%S).log"
echo "Test" > ${logfile}

output:

$ ./test.sh
./test.sh: line 3: ~/logs/20220114_025115.log: No such file or directory

I finally isolated the problem to the ~, and the workaround to my problem is to use $HOME or hard-code the full path (boo!), but my question is why does the ~ operator not get expanded to be my home directory? I googled for an answer, but nothing quite matches my question. Thanks in advance.

Answer 1

Tilde expansion occurs only when the tilde character is unquoted. From the bash manual:

If a word begins with an unquoted tilde character (‘~’), all of the characters up to the first unquoted slash (or all characters, if there is no unquoted slash) are considered a tilde-prefix.

https://www.gnu.org/software/bash/manual/html_node/Tilde-Expansion.html

You can force the expansion by moving the quote to the position after the first slash character. That is, from "~/logs/$(date +%Y%m%d_%H%M%S).log" to ~/"logs/$(date +%Y%m%d_%H%M%S).log".