Re: Detecting if a string is a regular expression

To test if a string contains regex metachars, quotemeta it and compare it to the original:

print "$_: does", ($_ eq quotemeta() ? 'not' : '' ), 'contain metachar
+s' 
    for 'a.c', '[abc]', 'abcd';;
a.c: does  contain metachars
[abc]: does  contain metachars
abcd: does not contain metachars
[download]

Of course, that doesn't test if the metachars make sense as a regex.

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Comment on Re: Detecting if a string is a regular expression Download Code

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Re^2: Detecting if a string is a regular expression by LanX (Saint) on Jan 12, 2013 at 11:03 UTC
for completeness: > Of course, that doesn't test if the metachars make sense as a regex let's Perl parse Perl =) `$ perl -ple ' $_ = eval "sub { /$_/ }" ? "OK\n" : "$@" ' a OK a( Unmatched ( in regex; marked by <-- HERE in m/a( <-- HERE / at (eval 2 +) line 1, <> line 2. a[ Unmatched [ in regex; marked by <-- HERE in m/a[ <-- HERE / at (eval 3 +) line 1, <> line 3. a() OK` [download] Cheers Rolf UPDATE unfortunately not always correct: `$ perl -ple ' $_ = eval "sub { /$_/ }" ? "OK\n" : "$@" ' a[$] OK` [download] but `$ perl -e ' "abc" =~ /a[$]/ ' Unmatched [ in regex; marked by <-- HERE in m/a[ <-- HERE 5.010000/ at + -e line 1.` [download] UPDATE interesting, this happens because it's a run-time error ... (why?) `$ perl -e 'sub {"aaa" =~ /a[$]/}' $ perl -e '"aaa" =~ /a[$]/' Unmatched [ in regex; marked by <-- HERE in m/a[ <-- HERE 5.010000/ at + -e line 1. $ perl -ce '"aaa" =~ /a[$]/' -e syntax OK` [download] looks like a parser problem for me! UPDATE variable interpolation is part of the problem, `a[$]` is a valid pattern, as long as it's not interpolated: `perl -E 'say q(a$) =~ q(a[$]) ' 1` [download] UPDATE this is very reliable `perl -ple ' $_ = eval "sub { 'a' =~ q\0$_\0 }" ? "OK\n" : "$@" '` to avoid problems with \0-delim consider using here-docs instead, or even a pack/unpack combination	[reply] [d/l] [select]

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Re^2: Detecting if a string is a regular expression
by LanX (Saint) on Jan 12, 2013 at 11:03 UTC

> Of course, that doesn't test if the metachars make sense as a regex

let's Perl parse Perl =)

$ perl -ple ' $_ = eval "sub { /$_/ }" ? "OK\n" : "$@" '
a
OK

a(
Unmatched ( in regex; marked by <-- HERE in m/a( <-- HERE / at (eval 2
+) line 1, <> line 2.

a[
Unmatched [ in regex; marked by <-- HERE in m/a[ <-- HERE / at (eval 3
+) line 1, <> line 3.

a()
OK
[download]

Cheers Rolf

UPDATE

unfortunately not always correct:

$ perl -ple ' $_ = eval "sub { /$_/ }" ? "OK\n" : "$@" '
a[$]
OK
[download]

but

$ perl -e ' "abc" =~ /a[$]/ '
Unmatched [ in regex; marked by <-- HERE in m/a[ <-- HERE 5.010000/ at
+ -e line 1.
[download]

UPDATE

interesting, this happens because it's a run-time error ... (why?)

$ perl -e 'sub {"aaa" =~ /a[$]/}'
$ perl -e '"aaa" =~ /a[$]/'
Unmatched [ in regex; marked by <-- HERE in m/a[ <-- HERE 5.010000/ at
+ -e line 1.
$ perl -ce '"aaa" =~ /a[$]/'
-e syntax OK
[download]

looks like a parser problem for me!

UPDATE

variable interpolation is part of the problem, a[$] is a valid pattern, as long as it's not interpolated:

perl -E 'say q(a$) =~ q(a[$]) '
1
[download]

UPDATE

this is very reliable

perl -ple ' $_ = eval "sub { 'a' =~ q\0$_\0 }" ? "OK\n" : "$@" '

to avoid problems with \0-delim consider using here-docs instead, or even a pack/unpack combination

[reply]
[d/l]
[select]