All Questions
569 questions
0
votes
2
answers
99
views
How can I run if statements on a command output without terminating it?
I have to run four separate if statements (and their consequences) on one command output continuously as it updates (doing four different things based on four different strings which might be in the ...
0
votes
1
answer
42
views
What is (if any) the file descriptor of /dev/tty?
The urgent issue to read keyboard input in the pipeline is solved by the answer in https://stackoverflow.com/questions/15230289/read-keyboard-input-within-a-pipelined-read-loop:
mycommand-outputpiped |...
- 1,363
3
votes
2
answers
113
views
What explains this very odd behavior of GNU grep interacting with buffering and pipes and how to stop it?
This is best illustrated with an example I feel:
{ printf 'foo\nbar\n' ; sleep 2 ; } | grep -m1 foo
{ printf 'foo\n' ; sleep 2 ; printf 'bar\n' ; sleep 2 ; } | grep -m1 foo
Both of these commands, ...
- 171
3
votes
2
answers
86
views
print_one_line_and_wait_long_time | head -n1: early exit of pipe/process substitution [duplicate]
tl;dr: How to reliably ensure that the pipe a | head -n1 terminates as soon as head terminates?
Motivation: git log --grep="$MAIL_SUBJECT_LINE" --oneline --format=%H | head -n1 takes a long ...
- 361
1
vote
1
answer
48
views
Is it possible to pipe command output to fd3 of another process?
Normally, we can pipe stdout to stdin as follows:
echo "This is going to stdout" | grep -o going
Suppose instead of grep I wrote a script that reads from both stdin and fd3, and then ...
- 4,099
3
votes
3
answers
183
views
How to quit from a pipeline "command1 | command2" while keeping a background subprocess launched by command1 alive?
Regarding the command cmd1.sh | grep "message", in which cmd1.sh is as below
#!/bin/bash
echo "message from foreground father proess$(date)"
setsid sleep 100 &
echo "...
- 204
0
votes
1
answer
48
views
watch with piped command executes differently than command itself
What am I doing wrong setting up following watch command? This works:
ls -ltr ~/meteofetcher/data/metar/2024/12 | tail -10 | awk '{ print $9 }' | xargs -I {} grep 'LSZH' {}
But this
watch "ls -...
- 117
0
votes
2
answers
86
views
Piping output to bash script
I'm going through the "sed & awk" book by Dougherty and Robbins. One of the examples calls for piping output to a shell script:
sed -f nameState list | byState
But I've found that, in ...
- 103
6
votes
1
answer
749
views
bash pipe loses data when command crashed
Consider this simple program (abort.py) that writes some text to stdout and stderr and then crashed (abort()).
import os
import sys
print("end stdout")
print("end stderr", file=...
- 171
3
votes
2
answers
1k
views
How to pipe input to an interactive shell in Bash
I want to do something like this:
echo whoami | sh
The command whoami runs in sh, but because the pipeline as a whole runs in a subshell, the sh interpreter exits instead of giving me a shell prompt. ...
- 859
3
votes
0
answers
131
views
Understanding piping to a unix domain socket in the background
I have a Debian 12 (bookworm) host where I run three VMs using QEMU / KVM. To simplify VM management, each VM has a QEMU monitor socket. These sockets are /vm/1.sock, /vm/2.sock and /vm/3.sock. Among ...
- 3,809
7
votes
1
answer
688
views
FIFO capture using cat not working as intended?
Hi I am trying to use a Unix FIFO to communicate between a Python script and a shell script. The intention is for the shell script to capture all output of the python script. So far I have the ...
- 345
1
vote
0
answers
45
views
Bash: export does not work if preceeds a pipe redirection [duplicate]
Example 1 (export and tee):
$ export var=1 | tee /dev/null
$ echo $var
$
Example 2 (null command between export and pipe):
$ export var=1 && : | tee /dev/null
$ echo $var
1
export sets var ...
0
votes
2
answers
58
views
Difference in bash output redirections behavior
I am trying to understand the reason behind the difference in redirections of bash output. Here are two approaches:
Redirection of the output to named pipe: /bin/bash -i 2>&1 1>/tmp/fifo
...
- 1
2
votes
1
answer
76
views
Is there a way to `exec` a pipeline or exit shell after launching a pipeline?
I'm writing a shell wrapper script that is supposed to act as a pager (receiving input on stdin and performing output on a tty).
This wrapper prepares environment and command lines, then launches two ...
- 5,659