Bash - Extract Matching String from GZIP Files Is Running Very Slow - bash

Question

Complete novice in Bash. Trying to iterate thru 1000 gzip files, may be GNU parallel is the solution??
#!/bin/bash
ctr=0
echo "file_name,symbol,record_count" > $1
dir="/data/myfolder"
for f in "$dir"/*.gz; do
gunzip -c $f | while read line;
do
str=`echo $line | cut -d"|" -f1`
if [ "$str" == "H" ]; then
if [ $ctr -gt 0 ]; then
echo "$f,$sym,$ctr" >> $1
fi
ctr=0
sym=`echo $line | cut -d"|" -f3`
echo $sym
else
ctr=$((ctr+1))
fi
done
done
Any help to speed the process will be greatly appreciated !!!

Answer 1

#!/bin/bash
ctr=0
export ctr
echo "file_name,symbol,record_count" > $1
dir="/data/myfolder"
export dir
doit() {
f="$1"
gunzip -c $f | while read line;
do
str=`echo $line | cut -d"|" -f1`
if [ "$str" == "H" ]; then
if [ $ctr -gt 0 ]; then
echo "$f,$sym,$ctr"
fi
ctr=0
sym=`echo $line | cut -d"|" -f3`
echo $sym >&2
else
ctr=$((ctr+1))
fi
done
}
export -f doit
parallel doit ::: *gz 2>&1 > $1

Answer 2

The Bash while read loop is probably your main bottleneck here. Calling multiple external processes for simple field splitting will exacerbate the problem. Briefly,
while IFS="|" read -r first second third rest; do ...
leverages the shell's built-in field splitting functionality, but you probably want to convert the whole thing to a simple Awk script anyway.
echo "file_name,symbol,record_count" > "$1"
for f in "/data/myfolder"/*.gz; do
gunzip -c "$f" |
awk -F "\|" -v f="$f" -v OFS="," '
/H/ { if(ctr) print f, sym, ctr
ctr=0; sym=$3;
print sym >"/dev/stderr"
next }
{ ++ctr }'
done >>"$1"
This vaguely assumes that printing the lone sym is just for diagnostics. It should hopefully not be hard to see how this can be refactored if this is an incorrect assumption.