I want to find a command that can judge a string match the specified regular expression or not .
e.g. command "abc486de" "ab*\d*e\b"
Match, return success code
not match , return failed code, and promote why not match.
What is the command? Thanks!

[[ abc486de =~ ab*\d*e\b ]] && echo yes || else echo no

That's for bash. is that what you're after? Not a particularly valid regex in your example though.

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*nix is all about regex. Bash, find, grep, sed, awk, vi, and even less, can handle it in some form or other.

The exact solution you'll want to use depends on the context of your problem. Tell us what you need to do, and we'll help you figure it out.

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Thanks ,the above is what I want.
I had thought there exists a command that can do a match. Maybe I am wrong.

Does "&&" acts for "and", "||" acts for "or" ?

well that does do "a match" if it... matches... which that regex doesn't. some context about your actual requirements would probably help.

I just want to judge if a string match a regular expression or not. I do not want to find or cut some line by using awk or grep. So "if" command is enough for me. But what's difference between "if [ ] " and "if [[ ]] "
Thanks.

[ is a symlink to the /bin/test command whereas [[ is built in to bash syntax. Using [[ bash will understand the command as a logic comparison but using [ to bash it's just a bunch of characters it passes on like any other command line, expanding variables, causing whtespace issues, null value problems etc. use [[.

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See here for the differences between [ and [[:
http://mywiki.wooledge.org/BashFAQ/031

BTW, bash's [ is also a shell built-in, but it mostly duplicates /bin/test. You still need to use [[ for advanced regex operation.

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Sorry, I have never used [[ ]] , and I don't understand Can you explain more ? Thanks!

ok, so you have a variable, BOB:

BOB="hello I am a string"

if you run something like

if [ -z $BOB ] ...

then that would be expanded by bash before evaluation as by the [ / test command as

if [ -z hello I am a string ]

which is nonesense, as each word is taken to be a different parameter passed to [. SO you have to do ugly things like wrap the variable name in quote marks etc.

using [[, the test work is done by bash itself. it doesn't replace $BOB, it *understands* that $BOB is a variable being used as part of a logic test so evaluates it correctly within its own code, behaving much more like a normal programming language.

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"[" is a command, a synonym for "test". That means that everything following it is just an argument to the command, like any other.

"[[" is a bash keyword, an internal function that follows special parsing rules. This means that it can do things and handle certain kinds of syntax that would choke the older command, such as regular expressions.

If you really want to learn things like this, start by reading this guide. It will give you all the basic concepts you need to know.
http://mywiki.wooledge.org/BashGuide

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Sorry , I had studied http://mywiki.wooledge.org/BashFAQ/031, I understood now.
But "&&" after ]] seems act for "if then", "||" act for "else then", not the meaning of "and" "or" .
What's my understanding is ,if success , run , if error, run echo no.
I have it ?

Inside a test construct:

If x evaluates as true, then also evaluate y. If y is also true, then the whole expression is true. If either one evaluates as false, then the whole expression is false. So both x and y must be true for the test to succeed.

If x evaluates as false, then also evaluate y. If y is also false, then the whole expression is false. If either one evaluates as true, then the whole expression is true. So either x or y must be true for the test to succeed.



The behavior of the operators outside of the test construct is similar. It's not entirely equal to if-then-else, but it can usually be used as a shorthand for it.

If the exit code of command x (any command, not just test) is 0 (success), then also run command y. Otherwise skip it.

If the exit code of command x is >0 (failure) then also run command y. Otherwise skip it.

If x exits successfully, then run command y. Then if y exits successfully, skip z.

But if x fails, skip y. Then since the exit code of x is still >0, run z.

However, and this is the big difference, if x succeeds, and then y fails, then z will also run.

http://mywiki.wooledge.org/BashPitfa...d2_.7C.7C_cmd3

The thing to remember is that these two operators always base their actions on the status of the exit code of the command that preceded it, without consideration of the expression as a whole. && continues if the previous command succeeded, and || continues if the previous command failed.

As the link above points out, if you want to be completely safe, use a full if-then-else instead.

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Thanks all