As Aacini shows, it seems that many things fail within a pipe. echo hello | set /p var= echo here | call :function But in reality it’s only a problem to understand how the pipe works. Each side of a pipe starts its own cmd.exe in its own ascynchronous thread. That is the cause why … Read more
There is an internal Bash variable called $PIPESTATUS; it’s an array that holds the exit status of each command in your last foreground pipeline of commands. <command> | tee out.txt ; test ${PIPESTATUS[0]} -eq 0 Or another alternative which also works with other shells (like zsh) would be to enable pipefail: set -o pipefail … … Read more
If you have Python version >= 2.7, you can use subprocess.check_output which basically does exactly what you want (it returns standard output as string). Simple example (linux version, see note): import subprocess print subprocess.check_output([“ping”, “-c”, “1”, “8.8.8.8”]) Note that the ping command is using linux notation (-c for count). If you try this on Windows … Read more
First redirect stderr to stdout — the pipe; then redirect stdout to /dev/null (without changing where stderr is going): command 2>&1 >/dev/null | grep ‘something’ For the details of I/O redirection in all its variety, see the chapter on Redirections in the Bash reference manual. Note that the sequence of I/O redirections is interpreted left-to-right, … Read more
To use a pipe with the subprocess module, you have to pass shell=True. However, this isn’t really advisable for various reasons, not least of which is security. Instead, create the ps and grep processes separately, and pipe the output from one into the other, like so: ps = subprocess.Popen((‘ps’, ‘-A’), stdout=subprocess.PIPE) output = subprocess.check_output((‘grep’, ‘process_name’), … Read more
You’d be a little happier with the following. import subprocess awk_sort = subprocess.Popen( “awk -f script.awk | sort > outfile.txt”, stdin=subprocess.PIPE, shell=True ) awk_sort.communicate( b”input data\n” ) Delegate part of the work to the shell. Let it connect two processes with a pipeline. You’d be a lot happier rewriting ‘script.awk’ into Python, eliminating awk and … Read more