Shell Utilities

[problem]

1. You want to compare 2 streams, with byte offset and line numbers?
2. Pull off content with a byte offset?
3. Display lines before or after a pattern?
4. Send an email – upon job failure?

[/problem]

[solution]

The shell is a powerful beast! Anything is possible … with a little know-how. 🙂 See the examples.

[/solution]

[example]

1. md5sum TARBALL | awk '{print $1;}' | cmp - TARBALL.md5
   # cmp good for comparing output with file contents, or diffing files. Outputs byte offset and line number. md5sum creates a hash (checksum) of file.
2. dd bs=1 skip=106 if=infile
   # disk to disk copy, example outputs infile with offset of 106 bytes (block size of 1 byte, skip 106 bytes).
3. Ever needed to display a line before or after a pattern. Yep sure you can use Perl, but this is a bit simplier to work out.

   See the code here

   See a run through screen shot here

   Usage – ppgrep #1 #2 pattern file – where #1 is the number of lines prior to the pattern (could be 0) and #2 is number of lines post pattern.

4. Sending email upon UNIX cron failure

[/example]

[reference]

[tags]dd, cmp, md5sum, grep, sed, Unix Coding School[/tags]

• Linux Man Pages – dd command
• Linux Man Pages – cmp command
• Linux Man Pages – md5sum command
• Linux Man Pages – grep command
• Linux Man Pages – sed command
• Linux Man Pages – crontab command

[/reference]

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