Question

Sorry for bumpy topic name (feel free to edit if you find more fitting title after looking at problem).
Code sample equals 1000 words, so here we go:

if [ "$REGEX" != "" ]; then
        find $TEST_DIR -type f -regextype posix-extended -regex '^.*(status|stderr|stdout)-captured$' |                                  
        grep -E $REGEX |
        awk '{print(""$1" "$1)}' | sed 's/-captured$/-expected/' | 
        while read -r line; do mv -f $line; done 
else
        find $TEST_DIR -type f -regextype posix-extended -regex '^.*(status|stderr|stdout)-captured$' |
        awk '{print(""$1" "$1)}' | sed 's/-captured$/-expected/' |
        while read -r line; do mv -f $line; done
fi

What code does is not all that important, I’d just like to find more elegant way to either use “grep -E $REGEX” or not. I thought that conditdonal aliases could do the job just like I’m used to from shell usage, but they does not work inside scripts.

I could put in a condition, but I fear performance impact from multiple evaluations.

Any way to make the code “more elegant”?

Answer 1

One simple way is to use ^ (which always matches: it means “start-of-line”, which every line has) if $REGEX is unset or blank:

find $TEST_DIR -type f -regextype posix-extended -regex '^.*(status|stderr|stdout)-captured$' |
grep -E ${REGEX:-^} |
awk '{print(""$1" "$1)}' | sed 's/-captured$/-expected/' |
while read -r line; do mv -f $line; done

For that matter, you can combine it into the original find:

find $TEST_DIR -type f -regextype posix-extended \
     -regex '^.*(status|stderr|stdout)-captured$' \
     -regex ".*${REGEX}.*" |
awk '{print(""$1" "$1)}' | sed 's/-captured$/-expected/' |
while read -r line; do mv -f $line; done

and for that matter, you can merge all of the rest of your script into find as well:

find $TEST_DIR -type f -regextype posix-extended \
     -regex '^.*(status|stderr|stdout)-captured$' \
     -regex ".*${REGEX}.*" \
     -exec bash -c 'file="{}" ; mv -f "$file" "${file%-captured}-expected"' \;