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Full Discussion: Error with expr - "expr: syntax error"
Top Forums Shell Programming and Scripting Error with expr - "expr: syntax error" Post 302601362 by methyl on Thursday 23rd of February 2012 12:44:25 PM
Old 02-23-2012
1. The usage of curly braces {} and " " in displaying variable value - when we use which one?
echo "${filename}"
I have got into the habit of always putting quotes round string variables and strings because it prevents so many silly errors when a value contains spaces.
I have also got into the habit of using curly braces even when they are not strictly necessary because it makes the variable name totally unambiguous.
It also prevents errors like this:
Code:
# Didn't recognise variable
fred="abc"
echo $fred42
sh: fred42: Parameter not set.

# Spaces disappeared
fred="abc"
echo ${fred}42     displaced
abc42 displaced

# All working now. Spaces not lost
fred="abc"
echo "${fred}42     displaced"
abc42     displaced

2. use of back quote in value assignment to a variable and with expr command. For eg, the way I'm assigning tot_rec_count.
Quote:
act_rec_count=`expr ${tot_rec_count} - 1`
In ksh and Posix Shell whatever is between backticks is to be executed.
This more modern syntax is preferred. $((arithmetic)).
Code:
act_rec_count=$((${tot_rec_count} - 1))



Also, I wouldn't bother with an array.
Quote:
set -A folders horizon mysteryshopper rcc reference
echo ${folders[@]}
for i in ${folders[@]}
This works the same and imho is easier to read and easier to type:
Code:
for i in "horizon" "mysteryshopper" "rcc" "reference"

This User Gave Thanks to methyl For This Post:
jagari
 

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LEARN ABOUT ULTRIX

test

test(1) 						      General Commands Manual							   test(1)

Name
       test - test conditional expression

Syntax
       test expr
       [ expr ]

Description
       The  command  evaluates the expression expr.  If the value of expr is true, the command returns a zero exit status; otherwise, it returns a
       nonzero exit status.  The command also returns a nonzero exit status if no arguments are specified.

Options
       The following primitives are used to construct expr:

       -r file		   Tests if the file exists and is readable.

       -w file		   Tests if the file exists and is writable.

       -f file		   Tests if the file exists and is not a directory.

       -d file		   Tests if the file exists and is a directory.

       -s file		   Tests if the file exists and has a size greater than zero.

       -t [ fildes ]	   Tests if the open file, whose file descriptor number is fildes (1 by default), is associated with a terminal device.

       -z s1		   Tests if the length of string s1 is zero.

       -n s1		   Tests if the length of the string s1 is nonzero.

       s1 = s2		   Tests if the strings s1 and s2 are equal.

       s1 != s2 	   Tests if the strings s1 and s2 are not equal.

       s1		   Tests if s1 is not the null string.

       n1 -eq n2	   Tests if number1 equals number2.

       n1 -ge n2	   Tests if number1 is greater than or equal to number2.

       n1 -gt n2	   Tests if number1 is greater than number2.

       n1 -le n2	   Tests if number1 is less than or equal to number2.

       n1 -lt n2	   Tests if number1 is less than number2.

       n1 -ne n2	   Tests if number1 is not equal to number2.

       These primitives can be combined with the following operators:

       !expr		   Negates evaluation of expression.

       expr -a expr	   Tests logical and of two expressions.

       expr -o expr	   Tests logical or of two expressions.

       ( expr... )	   Groups expressions.

       The -a operator takes precedence over the -o operator.  Note that all the operators and flags are separate  arguments  to  Note	also  that
       parentheses are meaningful to the Shell and must be escaped.

See Also
       find(1), sh(1), test(1sh5)

																	   test(1)
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