regex condition matching anything except one of given patterns

Faki · 05-18-2022, 03:06 AM

How can I construct a regex condition that matches anything except one of the given patterns?

pan64 · 05-18-2022, 03:23 AM

obviously it depends on the language you use.
The usual way is something like this:

Code:

if sample ~ pattern
then
    do something
else
    do something else
fi

And now you can just skip the "then" part.

Faki · 05-18-2022, 03:50 AM

I want to specifically know if there is a not match regex operator when I am interested in not matching only. In case of bash scripts.

pan64 · 05-18-2022, 03:55 AM

the not match is problematic, especially if you have more than one patterns.

boughtonp · 05-18-2022, 09:21 AM

Quote:

Originally Posted by Faki

I want to specifically know if there is a not match regex operator when I am interested in not matching only. In case of bash scripts.

There is a regex concept called negative lookaheads, which succeeds when its sub-expression cannot match.

Bash's regex engine doesn't support these, but both Perl's and Python's do.

There might potentially be workarounds depending on what specifically you are trying to do, but - given the frequency you've been asking regex questions - you need to consider if Bash is the right tool - and indeed whether regex is enough for whatever you're trying to achieve. (Some of your questions suggest you may want to look at Antlr/Bison/etc.)

teckk · 05-18-2022, 02:08 PM

Quote:

How can I construct a regex condition that matches anything except one of the given patterns?

Code:

a=(Mary had a little lamb)
echo "${a[@]%Mary}"
echo "${a[@]%a}"
echo "${a[@]%little}"

Doesn't have to be done in one line.

Examples:

Code:

a=(1 2 3 4 5 6 7 8 9 0 a b c d e f g)

for i in "${a[@]}"; do
    if [[ "$i" != [0-9] ]]; then
        echo ""$i" in not a digit"
    else
        echo ""$i" is a digit"
    fi
done

for i in "${a[@]}"; do
    if [[ "$i" != [a-e] ]]; then
        echo "$i"
    fi
done

for i in "${a[@]}"; do
    if [[ "$i" != [037de] ]]; then
        echo "$i"
    fi
done

Code:

a="Mary had a little lamb"

if [[ "$a" =~ ^Mary ]]; then 
    echo ""$a", starts with Mary"
fi

if [[ "$a" != ^Bob ]]; then
    echo ""$a", does not start with Bob"
fi

Code:

a="How can I construct a regex condition 
that matches anything except one of the 
given patterns?"

while read line; do 
    if [[ "$line" != "given patterns?" ]]; then
        echo "$line"
    fi
done <<< "$a"

MadeInGermany · 05-18-2022, 04:24 PM

Attention:
!= is the negation of == and takes shell globs.
!~ would be the negation of =~ but bash does not yet support it.

Corrections:

Code:

if [[ "$a" != Bob* ]]; then
    echo "'$a' does not start with Bob"
fi

Code:

if ! [[ "$a" =~ ^Bob ]]; then
    echo "'$a' does not start with Bob"
fi

Code:

    if [[ "$line" != *"given patterns?"* ]]; then
        echo "$line"
    fi

Code:

    if ! [[ "$line" =~ "given patterns?" ]]; then
        echo "$line"
    fi