MicroPosts

• Bash script prelude

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

  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