expr syntax error

baosheng · 06-06-2005, 02:35 AM

Hi guys.I wrote a shell script.But it doesn't work well.Can you help me?
The script is

#!/bin/sh
echo "please input a file name"
read file_name
date
num=1
while [ $num -lt 10 ]
do
gzip $file_name
gzip -d *.gz
num=`expr $num +1`
done
date

and this is the executing result
[root@myENIAC program]# sh deflate_time.sh
please input a file name
xlxfg512.txt
Mon Jun 6 15:30:55 CST 2005
expr: syntax error
deflate_time.sh: line 6: [: -lt: unary operator expected
Mon Jun 6 15:30:55 CST 2005

slackie1000 · 06-06-2005, 02:55 AM

hi there,
i think this post is more appropriate in programming...
anyway...
change the line

Code:

num=`expr $num +1`

per

Code:

num=$((num+1))

a tip: use the bb code tags... make it easier to read.. thanks.
regards
slackie1000

XavierP · 06-06-2005, 03:14 AM

Moved: This thread is more suitable in Programming and has been moved accordingly to help your thread/question get the exposure it deserves.

baosheng · 06-06-2005, 03:14 AM

it ok now
thanks

osvaldomarques · 06-09-2005, 03:32 PM

Hi Baosheng,

Just for the record, the problem was given by the expression evaluator "expr" detected a syntax error; you wrote the expression as

Code:

num=`expr $num +1`

instead of

Code:

num=`expr $num + 1`

As the expression evaluator received just 2 arguments, it gave a syntax error, returning an empty string to "num" variable.
As this variable is not numeric anymore, the test operator "[" returns an error as it is comparing a non numeric variable using the numeric comparator "-lt".