Advanced Bash−Scripting Guide

Chapter 30. Debugging
The Bash shell contains no debugger, nor even any debugging−specific commands or constructs. [60] Syntax
errors or outright typos in the script generate cryptic error messages that are often of no help in debugging a
non−functional script.
Example 30−1. A buggy script
#!/bin/bash
# ex74.sh
# This is a buggy script.
a=37
if [$a −gt 27 ]
then
echo $a
fi
exit 0
Output from script:
./ex74.sh: [37: command not found
What's wrong with the above script (hint: after the if)?
Example 30−2. Missing keyword
#!/bin/bash
# missing−keyword.sh: What error message will this generate?
for a in 1 2 3
do
echo "$a"
# done # Required keyword 'done' commented out in line 7.
exit 0
Output from script:
missing−keyword.sh: line 10: syntax error: unexpected end of file
Note that the error message does not necessarily reference the line in which the error occurs, but the line
where the Bash interpreter finally becomes aware of the error.
Error messages may disregard comment lines in a script when reporting the line number of a syntax error.
What if the script executes, but does not work as expected? This is the all too familiar logic error.
Chapter 30. Debugging 319