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sed 's/pattern/change/g' to replace strings.

backtick: `command` shells run command line and SDTOUT in a variable.
equivalent to $(command)

Array in bash

declare -a array
array=(1 2 3)

  • array[@] to return all elements
  • #array[@] to return length of array
  • can overwrite elements using index accessing
  • slicing array[@]:N:M _ N = start, M = number of elements
  • appending array+=(elements)

Associate array -A

  • array=([key]=value [key]=value)
  • accessing key using !array[@]
  • appending array[key]=value

ìf []; then

else

fi


can use both arithmetic special notation with [] or (())

special conditional flags:

  • -e if file exists
  • -s if file exists and size > 0
  • -r if file exists and readable
  • -w if file exists and writeable

&& AND ; || OR

brace expansion in for loop

  • if i in {x..y..z}
  • do
  • something
  • done

3 expression syntax in for loop

  • for ((x=1;x<4;x+=1))
  • do
  • something
  • done

glob expansion for file

  • for file in books/*
  • do
  • something
  • done

crontab -e to edit