Questions tagged [file-descriptors]
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400 questions
4 votes
1 answer
869 views
Why does bash need file descriptor duplicating?
I found out I don't totally understand how bash file descriptors work. I would like to have some guidance here. I have a scenario where I need to read the content of a file, and for each line of the ...
- 718
1 vote
1 answer
152 views
coproc redirect to stdout
Suppose I have some process that when ready will output to stdout. Even though I want my script to run asynchronously with respect to that process, I still want the script to block and wait on that ...
- 273
5 votes
2 answers
451 views
How (internally) does fd3>&fd1 after { fd1>&fd3 } put back (or not) original fd into fd1? ("bad file descriptor")
`I'm reading an answer to https://stackoverflow.com/questions/692000/how-do-i-write-standard-error-to-a-file-while-using-tee-with-a-pipe/692009#692009, https://stackoverflow.com/a/14737103/5499118: { {...
- 1,319
3 votes
1 answer
187 views
Bash redirections - handling several filenames specially (man pages)
Please confirm/correct me. I've found related Duplication of file descriptors in redirection but that does not answer my specific question. From the The GNU Bash Reference Manual, section 3.6 ...
- 1,501
0 votes
0 answers
70 views
I want to print debug output on failure, but ERR trap doesn't fire
I want to only print the debug output on failure, this is my attempt: #!/bin/bash set -euo pipefail dt-api() { # shellcheck disable=SC2086 curl \ --fail-with-body \ --silent \ ...
- 325
0 votes
1 answer
121 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 |...
- 1,501
2 votes
2 answers
532 views
what is the meaning and usage of 2>&1 | tee /dev/stderr
for the following command output=$(cat $file | docker exec -i CONTAINER COMMAND 2>&1 | tee /dev/stderr) what is the meaning and usage of 2>&1 | tee /dev/stderr? I google and 2>&...
- 133
7 votes
1 answer
1k views
Why does MacOS always append to a redirected file descriptor even when told to overwrite? Ubuntu only appends when strictly told to append
Given the following code: out="$(mktemp)" rm -f "$out" clear printf '%s\n' 0 >"$out" { printf '%s\n' '1' >/dev/stdout printf '%s\n' '2' >/dev/stdout } &...
- 644
1 vote
0 answers
91 views
How to solve uninterruptible sleep process deadlock without reboot
I have a process stuck in uninterruptible sleep. The problematic syscall is a read syscall towards /dev/fd0, which is not backed by a real floppy drive. I am trying to use modprobe and rmmod (both ...
1 vote
1 answer
111 views
Are file permissions copied into the Open File Table?
I have a doubt on what the entry created in the Open File Table upon calling open() contains. The following schema from bytebytego seems quite good to understand the big picture of opening a file, ...
- 113
1 vote
1 answer
264 views
bash: script running in pm2 unable to access file descriptors files at /dev/fd/
I have script script.sh: #!/usr/bin/env bash # pm2 seems to always run in `bash` regardless of `#!` echo "running in $(readlink -f /proc/$$/exe)" # Redirect to both stdout(1) and stderr(2) ...
- 323
2 votes
1 answer
392 views
Shell/bash: Can I create a file descriptor to an existing file without emptying the file? [duplicate]
Context: I have cursory bash experience. I do not fully get file descriptors, just some basic usage. Trying to create a setup script. Most done, but a few "kinks" remain. So here is a newbie ...
- 23
0 votes
0 answers
31 views
How to bypass pipe detection? [duplicate]
A question at stackoverflow has answers that show the following way of detecting if standard output is a pipe: if [ -t 1 ] ; then echo terminal; else echo "not a terminal"; fi The -t flag ...
- 428
1 vote
0 answers
129 views
Is there a known linux kernel bug with two threads incorrectly getting back the same file descriptor number?
I've got a multithreaded program in which a sem_open with O_CREAT occasionally fails with EBADF. This is on an ARM linux 4.9.88, from NXP, on an embedded device. It is very difficult to reproduce, ...
- 111
1 vote
1 answer
913 views
Capturing output from a bash function without using a subshell [closed]
I have a bash script listening on a pipe for commands. When it sees a command it runs it. However, I would like it to support the "sideloading" of bash functions that can be called at a ...
- 9,379