How to apply a command to each line in pipe?-CodePudding

I want to apply a command to each line of piped stdin like so:

cat file.txt | grep ... | ./filter | wc -l

the problem is ./filter accepts only a single line of input and gives a single line of output. I've tried xargs but it spawns a subshell and I can't capture it's output to continue working with the result. Is there an easy way to do that?

CodePudding user response：

If it accepts a single line, then you should put it in a loop if you want to process multiple lines,

cat file.txt | 
  grep ...   | 
  while read line ; do
      echo "$line" | ./filter
  done       | 
  wc -l

CodePudding user response：

To call a command for each line you can read a line into a variable and use the variable as a standard input. (Also, let’s avoid UUOC.)

grep ... < file.txt |
while IFS= read -r line; do
  ./filter <<< "$line"
done |
wc -l

In this case it looks like things may get way easier if you instead write the whole filter in awk. Because it will give you wc -l for free (NR), plus line and record splitting and filtering better than what grep can do.