BASH scripting

• Links Python/OneLiners , Linux/zsh, https://devhints.io/bash

• Loop through list

  •       cl_iplist_FWext="Int1=41.1.1.2 brInt2=166.6.3.15 brInt3=146.2.2.2 brInt4=156.2.2.62"
          for i in ${cl_iplist_FWext}; do
              fw_ip=${i##*=}
              fw_int=${i%%=*}

• Loop counter increase

  loopcount=$((loopcount+1))

Add ~/bin to path e.g.

• [[ ":$PATH:" == *":$HOME/bin:"* || ":$PATH:" == *":~/bin:"* ]] && echo "~/bin is in PATH" || echo "~/bin is not in PATH"

Time/Date

• Calc seconds till REPORT_TIME="now" or REPORT_TIME="21h20"

  sleepseconds=$(( $(date +%s -d "$REPORT_TIME") - $( date +%s ) ))
  if [ "$sleepseconds" -lt "0" ]; then
      sleepseconds=$(( $(date +%s -d "tomorrow $REPORT_TIME") - $( date +%s ) ))
  fi

• Time in specific timezone

  $ echo "$(env TZ=UTC date -Is) / $(env TZ=Pacific/Auckland date -Is)"
  2020-02-26T22:17:55+00:00 / 2020-02-27T11:17:55+13:00
  
  env TZ="Pacific/Auckland" date +"%Y%m%d-%Hh%Mm%Ss%z"
  20230124-14h05m20s+1300

• Sleep with count down

  SleepCountdown() {
    sleepseconds=$1
    reportsec=${2:-60}
    while [ $sleepseconds -gt 0 ]; do
      echo -ne "       $((sleepseconds))s\033[0K\r"
      sleep $(( $sleepseconds < $reportsec ? $sleepseconds : $reportsec ))
      sleepseconds=$(($sleepseconds - $reportsec))
    done
    echo -ne "                 \033[0K\r"
    }

• Function to print elapsed time in readable format

  time_start=$(date +%s)
  function ElapsedTime() {
      # Prints lapsed time in user readable format, uses $1 or time since $time_start
      time_elapsed=${1:-$(( $(date +%s) - time_start))}
      eval "echo Elapsed time: $(date -ud "@$time_elapsed" +'$((%s/3600/24)) days %H hr %M min %S sec') $2"
  }
  ## call 
  ElapsedTime
  # or with seconds
  ElapsedTime 50000

• ### MAC os version

  #
  time_start=$(date +%s)
  function ElapsedMinutes() {
      # Prints lapsed time in minutes, uses $1 can append $2
      t=$( awk -v t="${1:-$(( $(date +%s) - ${time_start} ))}" -v m="${2:-}" 'BEGIN {printf("%.2f%s", t / 60.0, m )}' )
      echo "$t"
  }
  # ElapsedMinutes
  # ElapsedMinutes $(( $(date +%s) - ${time_start} )) minutes

pipe stdout and stderr to two different processes in shell script?

• From https://stackoverflow.com/questions/9112979/pipe-stdout-and-stderr-to-two-different-processes-in-shell-script/31151808#31151808

• in bash

  command1 > >(command2) 2> >(command3)

• Posix

  { command 2>&1 1>&3 3>&- | stderr_command; } 3>&1 1>&2 | stdout_command

Description of bash components used in script below.

"$@"

• is all the command line parameters as a list

set -- "$@" "$1"

• adds the first command line parameter to end of list, making it one longer

shift

• shift's the command line parameters to the left, reducing them by one

$#

• Is the length or number of command lime parameters.
• One way to use all of this, is where we want to loop through all the command line parameters, filtering some of changing them is some way.

Here is an example that filters a specific parameter (e.g --values=xyz). It loops through all of them adding the ones we want to keep to the end and shifting left dropping the first one every-time.

argc=$#
j=0
while [ $j -lt $argc ]; do
    case "$1" in
         --values=?*)
              # do nothing remove this
              ;;
         *)
              set -- "$@" "$1"
              ;;
    esac

    shift
    j=$((j + 1))
done

Bash arrays(list) associative arrays(maps/dict)

• https://www.baeldung.com/linux/bash-array

• Indexed array eg.

  declare -a indexed_array=("Baeldung is" "so much" "cool")
  echo "Size of array:" ${#indexed_array[@]}
  echo "With quotes:"
  for element in "${indexed_array[@]}"
      do
          echo "["$element"]"
      done
  unset indexed_array[0]

• associative array e.g.

  declare -A associative_array=(["one"]="Baeldung" ["two"]="is" ["three"]="cool")
  for key in ${!associative_array[@]}
      do
          echo "["$key"]:["${associative_array[$key]}"]"
      done

Print 100 blank lines

 printf '\n%.s' {1..100} 

...

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CategoryLinux