MicroPosts

• What happens when you Ctrl-C

  When yout Ctrl-C in the terminal, SIGINT is sent to all the processes that belong to the foreground process group id (TPGID). (The same is true for any signals generated by the keyboard: SIGTSTP, SIGINT, etc.)

  To find the TPGID, you can ps -O tpgid. For example, if I run ser bin/dev in a Rails app (ser is a local reverse-proxy I wrote):

    PID TPGID   TT  STAT      TIME COMMAND
   1444  2822 s000  S      0:00.90 -zsh
   2822  2822 s000  S+     0:01.68 /Users/riccardoodone/.rvm/gems/ruby-3.4.4/gems/ser-0.1.0-x86_64-darwin/exe/x86_64-darwin/ser bin/dev
   3484  2822 s000  S+     0:00.64 foreman: main
   3509  2822 s000  S+     0:06.32 puma 7.0.4 (tcp://localhost:3000) [rictionary]
   3510  2822 s000  S+     0:12.17 sidekiq 8.0.8 rictionary [0 of 7 busy]
   3535  2822 s000  S+     0:00.10 puma: cluster worker 0: 3509 [rictionary]
   3536  2822 s000  S+     0:00.10 puma: cluster worker 1: 3509 [rictionary]
   3537  2822 s000  S+     0:00.11 puma: cluster worker 2: 3509 [rictionary]
   3538  2822 s000  S+     0:00.10 puma: cluster worker 3: 3509 [rictionary]
   3539  2822 s000  S+     0:00.10 puma: cluster worker 4: 3509 [rictionary]
   3540  2822 s000  S+     0:00.10 puma: cluster worker 5: 3509 [rictionary]
  

  If you wanted to simulate a Ctrl-C programmatically, you could send a signal to the -TPGID (minus means process group):

  kill -INT -2822
  

  More details in this wonderful Stack Overflow answer.

• Bash script prelude

  #!/usr/bin/env bash
  
  set -euo pipefail
  IFS=$'\n\t'
  set -x
  

  Explanation:

  #!/usr/bin/env bash: interpret the subsequent lines with bash

  ---

  set -e: exit immediately with error

  Script:

  echo 1
  not-existing-command
  echo 2
  

  Out:

  1
  not-existing-command: command not found
  2
  

  Script:

  set -e
  
  echo 1
  not-existing-command
  echo 2
  

  Out:

  1
  not-existing-command: command not found
  

  ---

  set -u: exit immediately with unbound variable

  Script:

  echo 1
  echo $NOT_EXISTING_VARIABLE
  echo 2
  

  Out:

  1
  
  2
  

  Script:

  set -u
  
  echo 1
  echo $NOT_EXISTING_VARIABLE
  echo 2
  

  Out:

  1
  NOT_EXISTING_VARIABLE: unbound variable
  

  ---

  set -o pipefail: make errors fall through pipelines

  Script:

  not-existing-command | sort
  echo $?
  

  Out:

  not-existing-command: command not found
  0
  

  Script:

  set -o pipefail
  
  not-existing-command | sort
  echo $?
  

  Out:

  not-existing-command: command not found
  127
  

  ---

  IFS=$'\n\t': Set input field separator (default: $' \n\t')

  Script:

  string="1 2 3"
  
  for i in $string; do
    echo "$i"
  done
  
  IFS=$'\n\t'
  for i in $string; do
    echo "$i"
  done
  

  Out:

  1
  2
  3
  1 2 3
  

  Script:

  array=(
  "a b"
  "c d"
  )
  
  for x in ${array[@]}; do
    echo "$x"
  done
  
  IFS=$'\n\t'
  for x in ${array[@]}; do
    echo "$x"
  done
  

  Out:

  a
  b
  c
  d
  a b
  c d
  

  ---

  set -x: print lines as they are executed

  Script:

  set -x
  
  echo 0
  echo 1
  

  Out:

  + echo 0
  0
  + echo 1
  1