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

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.
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.
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

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.
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

The verbose option is set and unset within the script.
The ––> marks where verbose was turned on. The lines are printed just as they were typed in the script and then executed.

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