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Using BASH =~ regex to match multiple strings


 
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# 1  
Old 04-28-2014
Using BASH =~ regex to match multiple strings

I have a scripting problem that I'm trying to solve, whereby I want to match that a string contains either of three strings. I'm thinking this is probably just me not understanding how to craft the appropriate regex. However, here's what I would like to do:

Code:
[[ $STRING =~ "one|two|three" ]] && do-something

more specifically:

Code:
[[ $STRING =~ "one OR two OR three" ]] && do something || :

I'd like to be able to match based on whether it has one or more of those strings -- or possibly all.

I'm sure this is simple, I just can't get my brain around it.

I know that BASH =~ regex can be system-specific, based on the libs available -- in this case, this is primarily CentOS 6.x (some OSX Mavericks with Macports, but not needed)


Thanks!

Last edited by radoulov; 04-28-2014 at 03:10 PM..
# 2  
Old 04-28-2014
Omit the quotes
Code:
[[ $STRING =~ one|two|three ]] && do-something

While I currently have no clue if it is advisable to quote "$STRING".
# 3  
Old 04-28-2014
Quote:
Originally Posted by MadeInGermany
Omit the quotes
Code:
[[ $STRING =~ one|two|three ]] && do-something

While I currently have no clue if it is advisable to quote "$STRING".
You don't need to do so because neither word splitting nor pathname expansion(globbing) are performed in this context.
This User Gave Thanks to radoulov For This Post:
# 4  
Old 04-28-2014
Quote:
Originally Posted by forrie
I have a scripting problem that I'm trying to solve, whereby I want to match that a string contains either of three strings. I'm thinking this is probably just me not understanding how to craft the appropriate regex. However, here's what I would like to do:

Code:
[[ $STRING =~ "one|two|three" ]] && do-something

more specifically:

Code:
[[ $STRING =~ "one OR two OR three" ]] && do something || :

[...]
When you quote the ERE in <STRING> =~ <ERE>, it's taken literally.
# 5  
Old 04-28-2014
So am I to infer from the responses that what I am attempting to do cannot be done in this context within BASH?

FYI, this does not work:

Code:
[[ "$1" =~ "one|two|three" ]]

basically, I'm looking to generate a positive result if it matches any of those words.

I've seen other examples (in different context) that will do something:

Code:
[[ "$1" =~ (regex) ]]

but with the emphasis that "regex" is very much platform-dependent (ie: depends highly on the regular expressions libs available on that system.

I could do something more verbose like this, but it defeats the purpose of succinct code:

Code:
[[ "$1" =~ "one" ]] || [[ "$1" =~ "two" ]] || [[ "$1" =~ "three" ]]

or more verbose using:

Code:
if [ "$1" =~ "one" ]
then
  do something
elseif [  "$1" =~ "two" ]
  do another-thing
elseif [ "$1" =~ "three" ]
  do that
else
  echo No match
fi

That's horrible to look at.
# 6  
Old 04-28-2014
Also it would need to be (bash/ksh93/zsh):
Code:
[[ $STRING =~ ^(one|two|three)$ ]] && do-something

or
Code:
if [[ $STRING =~ ^(one|two|three)$ ]]; then
  do_something
fi

or, using a case statement
Code:
case $STRING in 
  one|two|three) do_something
esac

# 7  
Old 04-28-2014
On CentOS 6.5, I am unable to get this to work correctly (per above):

Code:
[[ $STRING =~ ^(one|two|three)$ ]] && do-something

The string will actually be a part of a hostname, for example "one-hostname" or something like that. I need it check that there's a match, possibly doing something based on what it matched. But in this case the match word will be at the beginning ^one.
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