When most people start programming Bourne shell scripts they are VERY small. If you take over someone else's work or you have been programming shell scripts for any significant length of time, you will find something wrong in a script of thousands of lines.
Originally you might have put a few echo statements to see what was going wrong with a script. With thousands of scripts, scripts calling scripts, aliases set to scripts, system commands written as scripts, etc. it can get quite difficult to find a bug using echo statements.
The solution is to run the script with the -x flag. If you have the script starting with:
#!/bin/sh
then you can edit it to be:
#!/bin/sh -x
Or better yet, if the script is run using:
./myscript.sh
change it by using:
sh -x ./myscript.sh
Running the script with this option will let you see each line as it is executed. You will also see variables getting expanded. With this output the echo statements should be unnecessary. Try running a small script with this option and see what it outputs.
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