unexpected "then" expecting "done" in dash : how will I insert an if condition inside a for loop in dash?

Question

I'm using dash and I need to create CGI script that will parse the query string and save each value to a variable

OLDIFS=$IFS                
// use & as delimeter
IFS='&'

//this will loop the queryString variable               
for line in $queryString;  
do     
//check if the key = action, if the condition was satisfied it will save the line to a variable..
//if the key is equal to type etc. etc.                                                 
        echo "{$line,1}"                                                   
        if[{$line,0:7}="action="]
                then
                cgi_action={$line:8}
        elif[{$line:0:5}="type="]
                then
                cgi_type={$line:6}                                  
        fi                       
done                             
IFS=$OLDIFS        

Im sure that I have errors to get the substring of the line (or string) but please let's focus on the error I get when I put an if statement inside a for loop. What's the correct way to write an if condition inside for loop in dash shell scripting.

Additional info, im using ubuntu 14.04,

Answer 1

Firstly, comments in shell scripts are #, not //, which means that your script is confusing dash when it tries to parse it.

Secondly, you have to put spaces around all the tokens in the if condition - It's actually a syntax error the way you've written it e.g. change the action test to:

if [ {$line,0:7} = "action=" ]

thirdly, dash doesn't support substring extraction, and even if it did, the correct format is:

${variable:start}
${variable:start:nchars}

If you want to use substring extraction then you should use bash rather than dash.

Thirdly, you've got an off-by one error in the index into the value extraction - you're dropping the first character in the string. e.g. you check from offset 0 for a length of 5 for the type= value, then you take everything from index 6, which is one greater than you should be using.

your code would better read something like:

OLDIFS=$IFS
# use & as delimeter
IFS='&'

#this will loop the queryString variable
for line in $queryString; do
    #check if the key = action, if the condition was satisfied it will save the line to a variable..
    #if the key is equal to type etc. etc.

    echo "${line:1}"
    if [ ${line:0:7} = "action=" ]; then
        cgi_action=${line:7}
    elif [ ${line:0:5} = "type=" ]; then
        cgi_type=${line:5}
    fi
done
IFS=$OLDIFS

Not that I would ever recommend using shell for CGI scripting