Why doesn't this bash expr command work? [duplicate]

As @Cory rightly pointed out, there should not be spaces around the equal sign or else bash will confuse COUNTER for a command.

COUNTER=$(expr $COUNTER + 1) 

going off-topic ...

That said, you could avoid having bash fork a subprocess by using the following alternatives:

• Using the bash builtin 'let' command:

  let COUNTER="COUNTER + 1" 

• or, using bash c-style expression:

  (( COUNTER++ )) 

In fact, your while loop can be written as:

for ((COUNTER=0; COUNTER <= 5 ; COUNTER++)) do echo "i will add this line to file mycreation">>./myfile done 

Breaking down the error message

When you were met with the error:

line 7: 0: command not found. '-----' '--' '------------------' | | | location | Description of error. culprit 

my guess is what you had on line 7 was

$COUNTER = `expr $COUNTER + 1` -------- -------------------- | | Evaluated to 0 | Evaluated to 1 

What bash ends up see is 0 = 1 and since bash statements are generally in the form command arg1 arg1 ..., bash interprets it as run the command 0 with arguments = 1. Thus the error message : 0: command not found.

When you removed the spaces around the equal sign, what bash ends up interpreting is:

0=1 

which means run command 0=1 with no arguments, hence the error 0=1: command not found.

Variable assignments should be in the form VAR_NAME=VALUE (without the $), so the syntax you should be using is:

COUNTER=`expr $COUNTER + 1` # or any of the variants above 

which bash evaluates and eventually interpret as:

COUNTER=2