Issue with RegEx in matching timestamp in filename in Linux bash

Question

I have the following code written to check if my filename ends with some format like given below. It is working when tested online at https://regex101.com/ but not in linux bash. Please help me find out the issue.

Ex: timestamp_foramt="^[\s\S]+_INFT_[0-9]{8}_[0-9]{6}[.][\w]+$" FNAME="Payments.test_INFT_20191218_075918.txt" #example if [[ ! $FNAME =~ $timestamp_foramt ]]; then echo non-format; else echo format; fi non-format

Please help me understand why it is not working in bash. Did I commit something wrong in regex for timestamp_foramt?

Maybe that's because of your quotes as described [here](https://stackoverflow.com/a/19327286/2498251) — Elad, Dec 18 '19 at 14:33
May be not. Because, I used the parameter in RHS, double quotes wont be replaced here in run time. — Srinivasarao Kotipatruni, Dec 18 '19 at 14:40
Yes, it is wrong as POSIX bracket expressions do not support shorthand Perl-like classes — Wiktor Stribiżew, Dec 18 '19 at 14:57

score 3 · Accepted Answer · answered Dec 18 '19 at 14:59

3

You can fix the current expression like this:

timestamp_foramt="^.+_INFT_[0-9]{8}_[0-9]{6}\.[[:alnum:]_]+$"
FNAME="Payments.test_INFT_20191218_075918.txt" #example
if [[ ! $FNAME =~ $timestamp_foramt ]]; then
  echo 'non-format';
else
  echo 'format';
fi;

See the online Bash demo.

Main points:

[\s\S] can be used in Perl and other NFA regex engines to match any character, in POSIX ERE, used in Bash, you may simply use a .
\w is better written as [[:alnum:]_] in POSIX ERE as it is more portable to match letters, digits and underscores.

answered Dec 18 '19 at 14:59

Wiktor Stribiżew

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`\w` is the same as `[[:word:]]` and you should quote `$FNAME`. Btw., the shorthand character classes seem work in my bash if they're not inside a bracket expression `[…]` like `\w+`. – Freddy Dec 18 '19 at 15:07
@Freddy If they are not inside POSIX bracket expressions they may work, yes. – Wiktor Stribiżew Dec 18 '19 at 15:08
@WiktorStribiżew Thank You so much. It is working!! – Srinivasarao Kotipatruni Dec 19 '19 at 07:32

Issue with RegEx in matching timestamp in filename in Linux bash

1 Answers1