How to use patterns in a case statement?
The man
page says that case
statements use "filename expansion pattern matching"开发者_StackOverflow.
case $1 in
req|reqs|requirements) TASK="Functional Requirements";;
met|meet|meetings) TASK="Meetings with the client";;
esac
logTimeSpentIn "$TASK"
I tried patterns like req*
or me{e,}t
which I understand would expand correctly to match those values in the context of filename expansion, but it doesn't work.
Brace expansion doesn't work, but *
, ?
and []
do. If you set shopt -s extglob
then you can also use extended pattern matching:
?()
- zero or one occurrences of pattern*()
- zero or more occurrences of pattern+()
- one or more occurrences of pattern@()
- one occurrence of pattern!()
- anything except the pattern
Here's an example:
shopt -s extglob
for arg in apple be cd meet o mississippi
do
# call functions based on arguments
case "$arg" in
a* ) foo;; # matches anything starting with "a"
b? ) bar;; # matches any two-character string starting with "b"
c[de] ) baz;; # matches "cd" or "ce"
me?(e)t ) qux;; # matches "met" or "meet"
@(a|e|i|o|u) ) fuzz;; # matches one vowel
m+(iss)?(ippi) ) fizz;; # matches "miss" or "mississippi" or others
* ) bazinga;; # catchall, matches anything not matched above
esac
done
I don't think you can use braces.
According to the Bash manual about case in Conditional Constructs.
Each pattern undergoes tilde expansion, parameter expansion, command substitution, and arithmetic expansion.
Nothing about Brace Expansion unfortunately.
So you'd have to do something like this:
case $1 in
req*)
...
;;
met*|meet*)
...
;;
*)
# You should have a default one too.
esac
if
and grep -Eq
arg='abc'
if echo "$arg" | grep -Eq 'a.c|d.*'; then
echo 'first'
elif echo "$arg" | grep -Eq 'a{2,3}'; then
echo 'second'
fi
where:
-q
preventsgrep
from producing output, it just produces the exit status-E
enables extended regular expressions
I like this because:
- it is POSIX 7
- it supports extended regular expressions, unlike POSIX
case
- the syntax is less clunky than case statements when there are few cases
One downside is that this is likely slower than case
since it calls an external grep
program, but I tend to consider performance last when using Bash.
case
is POSIX 7
Bash appears to follow POSIX by default without shopt
as mentioned by https://stackoverflow.com/a/4555979/895245
Here is the quote: http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_01 section "Case Conditional Construct":
The conditional construct case shall execute the compound-list corresponding to the first one of several patterns (see Pattern Matching Notation) [...] Multiple patterns with the same compound-list shall be delimited by the '|' symbol. [...]
The format for the case construct is as follows:
case word in [(] pattern1 ) compound-list ;; [[(] pattern[ | pattern] ... ) compound-list ;;] ... [[(] pattern[ | pattern] ... ) compound-list] esac
and then http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_13 section "2.13. Pattern Matching Notation" only mentions ?
, *
and []
.
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