[Chapter 46] 46.2 Quoting Trouble? Think, Then Use echo
Author: Jerry Peek, Tim O'Reilly & Mike Loukides
Date: 1998-08-04T21:55:37Z

#

| Chapter 46 Shell Script Debugging and Gotchas |

## 46.2 Quoting Trouble? Think, Then Use echo

Q: I can't get the following shell script to work:

Q:

>     case $col2 in
>     "income") awk '{if($2=='$col2') {   /* THIS LINE IS THE PROBLEM */
>               /* I CAN'T GET AWK TO RECOGNIZE EITHER '$col2' or '$2' */
>                     .
>                     .

>               } ' $file1 ;;

A: It is clear from this code fragment that awk is supposed to compare `$2` with `"income"`. If you think about it (or change `awk` to `echo` above), you will see that you have given the following to awk:

A:

>     {if($2==income) { /* THIS LINE IS THE PROBLEM */

A: What does awk do with this? It compares `$2` with the contents of the variable income. If income has not been set, it compares it with zero or with the null string. Instead, you want:

A:

>     { if ($2 == "income") {

A: which you can say with:

A:

>     case $col2 in
>     income)
>             awk '
>             {
>                     if ($2 == "'$col2'") {
>                             ... awk code ...
>                     }
>             }' $file1;;

Replacing commands with `echo` in shell scripts is a handy debugging trick.

- CT in net.unix on Usenet, 1 November 1986

46.1 Tips for Debugging Shell Scripts |  | 46.3 Bourne Shell Debugger Shows a Shell Variable