Diary and notebook of whatever tech problems are irritating me at the moment.


quote-count: A debugging tool for shell scripts

I've been doing a lot of shell scripting lately with Dash and Bash. Complicated scripts with lots of text handling make debugging difficult, especially when they are being used in sub-shells which obfuscate line numbers in error messages. One of my more common mistakes is an unmatched quote. These can be rather difficult to find so I wrote quote-count, a simple analysis tool that counts quotes in lines.

It just accepts a single filename as a parameter and counts single, double, and back quotes on each line and prints their totals. It prints out a warning if the any of the counts is odd-numbered which may indicate a mismatched quote. It also warns if the line is a comment so you easily ignore those. It isn't brilliant as it doesn't handle escaped newlines, in-line comments, escaped quotes or quotes encapsulated within other quotes. It could be enhanced to handle these cases but it's already saved me a lot of debugging time as is. The output from running it on itself looks like this:

1 Q:0 DQ:0 BQ:0 # COMMENT
2 Q:0 DQ:0 BQ:0 # COMMENT
3 Q:0 DQ:0 BQ:0 # COMMENT
4 Q:0 DQ:0 BQ:0 # COMMENT
5 Q:0 DQ:0 BQ:0 # COMMENT
6 Q:0 DQ:0 BQ:0 # COMMENT
7 Q:0 DQ:0 BQ:0 # COMMENT
8 Q:0 DQ:0 BQ:0
9 Q:0 DQ:8 BQ:0
10 Q:0 DQ:2 BQ:0
11 Q:0 DQ:2 BQ:0
12 Q:0 DQ:2 BQ:0
13 Q:0 DQ:2 BQ:0
14 Q:0 DQ:2 BQ:0
15 Q:0 DQ:0 BQ:0
16 Q:0 DQ:0 BQ:0
17 Q:0 DQ:0 BQ:0
18 Q:0 DQ:0 BQ:0
19 Q:0 DQ:0 BQ:0
20 Q:0 DQ:0 BQ:0
21 Q:0 DQ:2 BQ:0
22 Q:4 DQ:5 BQ:1 # ODD
23 Q:0 DQ:2 BQ:0
24 Q:5 DQ:4 BQ:1 # ODD
25 Q:0 DQ:2 BQ:0
26 Q:5 DQ:3 BQ:2 # ODD
27 Q:0 DQ:2 BQ:0
28 Q:0 DQ:4 BQ:0
29 Q:0 DQ:2 BQ:0
30 Q:0 DQ:2 BQ:0
31 Q:0 DQ:0 BQ:0
32 Q:0 DQ:0 BQ:0
33 Q:0 DQ:0 BQ:0

I've tested it with both Dash and Bash on Ubuntu 9.10 and Mandriva 2010.1 so it should work with most systems.

Another typo I occasionally encounter is escaped whitespace at the end of a line. The intent always is to escape a newline but sometimes in my editing I end up with a space or tab after the backslash. These can easily be found with grep:

grep -E -r -n '\\[[:space:]]+$'<filename>

I wanted to add this check to quote-count v1.0 but found that the "while read" loop removes everything after the trailing backslash. Richard Bos sent me a modified version that included the check as a pre-processor utilizing a simple grep trick. I added it in although it used an array which Dash doesn't support.

UPDATE: v1.2 released and link updated. I found some bugs in v1.1 with the TEW check. I also cleaned up the report output a bit.

Reading through the quote-count report for my larger scripts was tedious so I wrote quote-count-query which compares the original source file with the quote-count report and shows the affected lines with two preceding and following lines for context.

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About Me

Omnifarious Implementer = I do just about everything. With my usual occupations this means anything an electrical engineer does not feel like doing including PCB design, electronic troubleshooting and repair, part sourcing, inventory control, enclosure machining, label design, PC support, network administration, plant maintenance, janitorial, etc. Non-occupational includes residential plumbing, heating, electrical, farming, automotive and small engine repair. There is plenty more but you get the idea.