Bash chit-sheet

Some simple tricks that can make bash scripting a breeze:

1. To truncate a float to int:

   INT=${FLOAT/\.*}




2. To split a string (of 2 words) into its components:

   FIRST_WORD=${STRING%% *},SECOND_WORD=${STRING#* }




3. To do simple floating point arithmetic, use bc:

   AVERAGE=$(echo "scale=2; ($FLOAT1 + $FLOAT2 ) / 2" | bc )




4. Conditional if statement:

   if [[ $INT1 -gt $INT2 ]]; then echo greater; fi




5. To check the number of arguments for a bash script and to issue an error message if the number of arguments if insufficient, use the following code snippet at the top of the script:

   EXPECTED_ARGS=2

   E_BADARGS=65

   if [ $# -ne $EXPECTED_ARGS ]; then

   echo "Usage: ./script_name arg1 arg2"

   echo " Example: ./sum 1 2"

   exit $E_BADARGS

   fi

   
   



6. To find the process ID of a running process, use pgrep:

   pgrep -fl PROCESS_NAME




7. To kill a process using the process name instead of the process ID, use:

   kill $(ps -ef |grep PROCESS_NAME | grep -v grep | awk '{print $2}')




8. Find files that contain a text string:

   grep -lir "text to find" *

   The -l switch outputs only the names of files in which the text occurs (instead of each line containing the text), the -i switch ignores the case, and the -r descends into subdirectories.