ANDed conditional using regexp and variables

Question

I want to test whether a line, read in from a file, has a specific beginning AND an ending containing a word held in a variable. Here's some code:

The input file is:

line one
#; line two
#; line three blah
line four

A minimal script, which fails, is:

declare ENDOFLINE= "blah"
exec 3< "inputfile"

while read LINE <&3
do
    if [[ ("$LINE" =~ "^#;") && (( ("$LINE" =~ "${ENDOFLINE%$}") )) ]]; 
    then
    echo score!
    else echo no score
    fi
done

But, if I do:

if [[ ("$LINE" =~ "^#;") && (( ("$LINE" =~ "blah$") )) ]];

it succeeds in identifying the correct line (=> #; line three blah). In other words, I need a compound test condition where the first test is whether the beginning of the line is '#;' and the end of the line is a string contained in the variable $ENDOFLINE .

Thanks for any help.

Answer 1

Looks like a simple mistake: ${ENDOFLINE%$} strips a $ at the end of $ENDOFLINE, but what you want to do is use $ENDOFLINE literally and have a $ after it to indicate the end of the line.

if [[ ("$LINE" =~ "^#;") && (( ("$LINE" =~ "${ENDOFLINE}$") )) ]];

This works in zsh but not in ksh or bash. Bash requires the regexp $ to be unquoted (otherwise, it's interpreted literally), and ksh doesn't like double parentheses inside [[ … ]] (it interprets them as an arithmetic instruction). This simpler line works in all three shells (note that [[…]] is one of the few places where you don't need "…" around variable expansions):

if [[ $LINE =~ ^"#;" && $LINE =~ $ENDOFLINE$ ]];

If $ENDOFLINE never overlaps with #; (e.g. if ENDOFLINE is ;foo, you'll be accepting #;;foo but rejecting #;foo), you can reduce this to a single test:

if [[ $LINE =~ ^"#;".*$ENDOFLINE$ ]];

You can also use a wildcard pattern instead of a regexp here:

if [[ $LINE = "#;"*"$ENDOFLINE" ]];

The [[…]] construct doesn't exist in all shells, it's specific to bash, ksh and zsh. On other shells (Bourne, dash, anything POSIX), you can do wildcard matches with the case construct:

case $LINE in
  "#;"*"$ENDOFLINE") echo score;;
  *) echo no score;;
esac

Answer 2

You can also do this using grep:

end=blah
while read line; do
    if grep -Eq "^#;.*$end$" <<< "$line"; then
        echo score!
    else
        echo no score
    fi
done

(That's in bash; the syntax may be slightly different in other shells but the principle is the same.)