I am having trouble with pattern matching in zsh's hook function precmd. I have the following:
precmd(){
local x='test'
if [ $x = '*test*' ]; then
echo 'hello'
fi
}
which does not print hello ever. I've tested this code with a normal zsh test.zsh that works fine, and I've tried w/o the regex in precmd and got things to print out fine as well. Any clue as to why this isn't working as expected?
$ zsh --version
zsh 4.3.11 RHEL
[ $x = '*test*' ] tests whether the string resulting from expanding $x, which is text, is equal to the string resulting from expanding '*test*', which is *text*.
To test whether the value of the variable x matches the pattern *test*, you need to use the = or == operator of zsh conditional expressions, which are written within double brackets [[ … ]]. Furthermore special characters in the pattern must be unquoted, otherwise they stand for themselves. Thus:
if [[ $x == *test* ]]; then …
The syntax of conditional expressions is similar to the syntax of expressions that you can use within single brackets [ … ], but not identical. [ is parsed like an ordinary command; in fact, it's a built-in command with a one-character name, which is identical to the test builtin except that [ requires an additional argument at the end which must be ]. [[ … ]] is a distinct grammatical construct, which allows it to have shell special characters inside. [ $x = *test* ] would expand *test* to the list of matching file names (globbing) and the test builtin would end up parsing the result of that. [[ $x = *test* ]] parses *test* as part of conditional expression parsing which does not invoke globbing.
case $x in (*test*) ... ;esac syntax.
[[ "$x" == "{*, *}" ]] never return true ? Trying to match {0, 1} for example
* are in quotes, so only {*, *} matches. You need e.g. [[ "$x" == {*', '*} ]] or [[ "$x" == {*,\ *} ]] (braces don't need to be quoted in a glob pattern). Those also match e.g. {0, 1, 2} and {{{{{, } so maybe you want something like shopt -s extglob; [[ "$x" == {+([0-9]),\ +([0-9])} ]] or [[ "$x" =~ {[0-9]+,\ [0-9]+} ]] instead.
*test* is not a valid regex pattern. The * is a repetition operator and needs something to repeat. It's very likely you want .*test.*, although that isn't necessary with regex since it is not anchored by default. You could just look for test
However you cannot match regex patterns with the = operator, you need =~.
precmd () {
local x=test
if [[ $x =~ test ]]; then
echo 'hello'
fi
}
=~? You can keep the wildcard syntax and the = operator. The only thing that needs to change is to use [[ instead of [.
[[ $x =~ '.*test.*' ]] or [ "$x" '=~' '.*test.*' ] or [[ $x = *test* ]] (no quote there), or [[ $x =~ test ]]
if [[ "$x" =~ .*test.* ]]; then. Thanks
http://zsh.sourceforge.net/Doc/Release/Functions.htmland regex is a bit of a misnomer, actually a globbing pattern:http://zsh.sourceforge.net/Doc/Release/Expansion.html#Filename-Generation