将awk输出管道到C程序

Question

Hi I have written ac program that takes 3 integers as input:

./myprogram 1 2 3

and I am aiming to pipe data from a csv file into the input of the c program. I grab each line from the c program using:

for i in $(seq 1 `wc -l "test.csv" | awk '{print $1}'`); do sed -n $i'p' "test.csv"; done;

and then would like to pipe the output of this into my c program. I have tried doing:

for i in $(seq 1 `wc -l "test.csv" | awk '{print $1}'`); do sed -n $i'p' "test.csv"; done; | ./myprogram

however I get:

Line 
bash: syntax error near unexpected token `|'

how do I pipe the output into my c program?

Thanks

Answer 1

It helps when you really try to understand error messages the shell gives you:

Line 
bash: syntax error near unexpected token `|'

If you think about it, when you chain commands together in a pipeline, there is never a ; before a | , for example:

ls | wc -l
# and not: ls; | wc -l

Whatever comes after a ; is like an independent new command, as if you typed it on a completely new, clear command line. If you type | hello | hello on a clear command line, you'll get the exact same error, because that's the exact same situation as ; | ... ; | ... ; | ... in your script, for example:

$ | hello
-bash: syntax error near unexpected token `|'

Others already answered this, but I also wanted to urge you to make other improvements in your script:

1. Always use $() instead of backticks, for example:

    for i in $(seq 1 $(wc -l "test.csv" | awk '{print $1}')); ... 

2. You didn't need the awk there, this would work just as well:

    for i in $(seq 1 $(wc -l "test.csv")); ... 

3. You could reduce your entire script to simply this, for the same effect:

    ./myprogram < test.csv 

Answer 2

In the shell, it doesn't like an explicit line termination followed by a pipe ( | ). The pipe already delimits the commands. So you want:

for i in $(seq 1 `wc -l "test.csv" | awk '{print $1}'`); do sed -n $i'p' "test.csv"; done | ./myprogram