ash: -c: 未知操作数

Question

I'm trying to run a ash script that constantly checks how many characters are in a file and execute some code if it reaches at least 170 characters or if 5 seconds have passed. To do that I wanted to call wc -c , however it keeps telling me it has an unknown operand.

The code:

#!/bin/ash
while true; do
secs=5
endTime=$(( $(date +%s) + secs ))
while [ /usr/bin/wc -c < "/tmp/regfile_2" -gt 170 ] || [ $(date +%s) -lt $endTime ]; do

#more code

It's output is ash: -c: unknown operand

Answer 1

You want to check whether the output from wc meets a specific condition. To do that, you need to actually execute wc , just like you already do with date to examine its output.

while [ $(wc -c < "/tmp/regfile_2") -gt 170 ] ||
      [ $(date +%s) -lt $endTime ]; do
    # ...stuff

Notice the $(command substitution) around the wc command.

As you can see from the answer to the proposed duplicate Checking the success of a command in a bash `if [ .. ]` statement your current command basically checks whether the static string /usr/bin/wc is non-empty; the -c after this string is indeed unexpected, and invalid syntax.

(It is unclear why you hardcode the path to wc ; probably just make sure your PATH is correct before running this script. There are situations where you do want to hardcode paths, but I'm guessing this isn't one of them; if it is, you should probably hardcode the path to date , too.)