Why doesn't find let me match multiple patterns? - macos

Question

I'm writing some bash/zsh scripts that process some files. I want to execute a command for each file of a certain type, and some of these commands overlap. When I try to find -name 'pattern1' -or -name 'pattern2', only the last pattern is used (files matching pattern1 aren't returned; only files matching pattern2). What I want is for files matching either pattern1 or pattern2 to be matched.
For example, when I try the following this is what I get (notice only ./foo.xml is found and printed):
$ ls -a
. .. bar.html foo.xml
$ tree .
.
├── bar.html
└── foo.xml
0 directories, 2 files
$ find . -name '*.html' -or -name '*.xml' -exec echo {} \;
./foo.xml
$ type find
find is an alias for noglob find
find is /usr/bin/find
Using -o instead of -or gives the same results. If I switch the order of the -name parameters, then only bar.html is returned and not foo.xml.
Why aren't bar.html and foo.xml found and returned? How can I match multiple patterns?

Answer 1

You need to use parentheses in your find command to group your conditions, otherwise only 2nd -name option is effective for -exec command.
find . \( -name '*.html' -or -name '*.xml' \) -exec echo {} \;

Answer 2

find utility
-print == default
If you just want to print file path and names, you have to drop exec echo, because -print is default.:
find . -name '*.html' -or -name '*.xml'
Order dependency
Otherwise, find is read from left to right, argument order is important!
So if you want to specify something, respect and and or precedence:
find . -name '*.html' -exec echo ">"{} \; -o -name '*.xml' -exec echo "+"{} \;
or
find . -maxdepth 4 \( -name '*.html' -o -name '*.xml' \) -exec echo {} \;
Expression -print0 and xargs command.
But, for most cases, you could consider -print0 with xargs command, like:
find . \( -name '*.html' -o -name '*.xml' \) -print0 |
xargs -0 printf -- "-- %s -\n"
The advantage of doing this is:
Only one (or few) fork for thousand of entry found. (Using -exec echo {} \; implies that one subprocess is run for each entry found, while xargs will build a long line with as many argument one command line could hold...)
In order to work with filenames containing special character or whitespace, -print0 and xargs -0 will use the NULL character as the filename delimiter.
find ... -exec ... {} ... +
From some years ago, find command accept a new syntax for -exec switch.
Instead of \;, -exec switch could end with a plus sign +.
find . \( -name '*.html' -o -name '*.xml' \) -exec printf -- "-- %s -\n" {} +
With this syntax, find will work like xargs command, building long command lines for reducing forks.