10.4. Debugging Scripts

C/TC shell scripts often fail because of some simple syntax error or logic error. Options to the csh command to help you debug your programs are provided in Table 10.3.

Example 10.7.

 (The -v and -x Options) 1   %  cat practice   #!/bin/csh   echo Hello $LOGNAME   echo The date is `date`   echo Your home shell is $SHELL   echo Good-bye $LOGNAME  2   %  csh -v practice   echo Hello $LOGNAME   Hello ellie   echo The date is `date`   The date is Sun May 23 12:24:07 PDT  2004   echo Your login shell is $SHELL   Your login shell is /bin/csh   echo Good-bye $LOGNAME   Good-bye ellie  3   %  csh -x practice   echo Hello ellie   Hello ellie   echo The date is `date`   date   The date is Sun May 23 12:24:15 PDT  2004   echo Your login shell is /bin/csh   Your login shell is /bin/csh   echo Good-bye ellie   Good-bye ellie  

Table 10.3. echo (“x) and verbose (“v)

Option	What It Does
As Options to csh and tcsh
csh x scriptname tcsh -x scriptname	Display each line of script after variable substitution and before execution.
csh v scriptname tcsh -v scriptname	Display each line of script before execution, just as you typed it.
csh n scriptname tcsh -n scriptname	Interpret but do not execute commands.
As Arguments to the set Command
set echo	Display each line of script after variable substitution and before execution.
set verbose	Display each line of script before execution, just as you typed it.
As the First Line in a Script
#!/bin/csh xv #!/bin/tcsh -xv	Turns on both echo and verbose. These options can be invoked separately or combined with other csh invocation arguments.

EXPLANATION

1. The contents of the C shell script are displayed. Variable and command substitution lines are included so that you can see how echo and verbose differ .

2. The “v option to the csh command causes the verbose feature to be enabled. Each line of the script is displayed as it was typed in the script, and then the line is executed.

3. The “x option to the csh command enables echoing. Each line of the script is displayed after variable and command substitution are performed, and then the line is executed. Because this feature lets you examine what is being replaced as a result of command and variable substitution, it is used more often than the verbose option.

Example 10.8.

 (Echo and Verbose) 1   %  cat practice   #!/bin/csh   echo Hello $LOGNAME   echo The date is `date`   set echo   echo Your home shell is $SHELL   unset echo   echo Good-bye $LOGNAME   % chmod +x practice  2   %  practice   Hello ellie   The date is Sun May 26 12:25:16 PDT  2004  -->  echo Your login shell is /bin/csh  -->  Your login shell is /bin/csh  -->  unset echo   Good-bye ellie  

EXPLANATION

1. The echo option is set and unset within the script. This enables you to debug certain sections of your script where you have run into a bottleneck, rather than echoing each line of the entire script.

2. The “ “> marks where the echoing was turned on. Each line is printed after variable and command substitution and then executed.

Example 10.9.

 1   %  cat practice   #!/bin/csh   echo Hello $LOGNAME   echo The date is `date`   set verbose   echo Your home shell is $SHELL   unset verbose   echo Good-bye $LOGNAME  2   %  practice   Hello ellie   The date is Sun May 23 12:30:09 PDT  2004  -->  echo Your login shell is $SHELL  -->  Your login shell is /bin/csh  -->  unset verbose   Good-bye ellie  

EXPLANATION

1. The verbose option is set and unset within the script.

2. The “ “> marks where verbose was turned on. The lines are printed just as they were typed in the script and then executed.