Subtract two variables in Bash

Question

I have the script below to subtract the counts of files between two directories but the COUNT  expression does not work  What is the correct syntax      usr bin env bash  FIRSTV  ls -1   wc -l  cd    SECONDV  ls -1   wc -l  COUNT expr  FIRSTV- SECONDV     - gt  gives  command not found  error echo  COUNT

User · Answer

You can use     count   FIRSTV - SECONDV     to avoid invoking a separate process  as per the following transcript   pax    FIRSTV 7 pax    SECONDV 2 pax      count   FIRSTV - SECONDV   pax    echo  count 5

User · Answer

For simple integer arithmetic  you can also use the builtin let command    ONE 1  TWO 2  let  THREE    ONE    TWO   echo  THREE     3   For more info on let  look here

User · Answer

This is how I always do maths in Bash   count   echo   FIRSTV -  SECONDV  bc  echo  count

User · Answer

White space is important  expr expects its operands and operators as separate arguments  You also have to capture the output  Like this   COUNT   expr  FIRSTV -  SECONDV    but it s more common to use the builtin arithmetic expansion   COUNT    FIRSTV - SECONDV

User · Answer

Alternatively to the suggested 3 methods you can try let which carries out arithmetic operations on variables as follows   let COUNT  FIRSTV- SECONDV   or  let COUNT FIRSTV-SECONDV

User · Answer

Try this Bash syntax instead of trying to use an external program expr   count    FIRSTV-SECONDV     BTW  the correct syntax of using expr is   count   expr  FIRSTV -  SECONDV    But keep in mind using expr is going to be slower than the internal Bash syntax I provided above

User · Answer

You just need a little extra whitespace around the minus sign  and backticks   COUNT  expr  FIRSTV -  SECONDV    Be aware of the exit status   The exit status is 0 if EXPRESSION is neither null nor 0  1 if EXPRESSION is null or 0   Keep this in mind when using the expression in a bash script in combination with set -e which will exit immediately if a command exits with a non-zero status

User · Answer

Use Python      bin bash   home victoria test sh  START   date    s                                          seconds since Epoch for i in   seq 1 10  do   sleep 1 5   END   date    s                                          integer   TIME    END - START                                      integer   AVG TIME   python -c  print float  TIME  i               int to float   printf  i   i   elapsed time   0 1f sec   avg  time   0 3f n   i  TIME  AVG TIME     i                                                      increment  i done    Output      test sh  i  1   elapsed time  1 0 sec   avg  time  1 000 i  2   elapsed time  3 0 sec   avg  time  1 500 i  3   elapsed time  5 0 sec   avg  time  1 667 i  4   elapsed time  6 0 sec   avg  time  1 500 i  5   elapsed time  8 0 sec   avg  time  1 600 i  6   elapsed time  9 0 sec   avg  time  1 500 i  7   elapsed time  11 0 sec   avg  time  1 571 i  8   elapsed time  12 0 sec   avg  time  1 500 i  9   elapsed time  14 0 sec   avg  time  1 556 i  10   elapsed time  15 0 sec   avg  time  1 500      Get current time in seconds since the Epoch on Linux  Bash

[bash] Subtract two variables in Bash

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