Shell Tips and Tricks

[problem]

1. You want to trace program execution on Solaris?
2. You want to perform network tracing on Solaris?
3. Perform a text dump of a binary file – or see ascii codes, etc?
4. Generate some random data?
5. List directory contents in 3 columns?
6. Loop through a list of files and perform actions on them?
7. Check for values in vars?
8. Detach a process without it dying.
9. Perform arithmetic in shell.

[/problem]

[solution]

Some of the most useful Shell Tricks I’ve learned – check them out at Example – enjoy! 🙂

[/solution]

[example]

1. System process debug (solaris) all exec/reads

   truss -xall -vall -rall -t'read' -p PID

2. Network trace connection from hostname (solaris)

   snoop -x0 src hostname

3. Optical dump of a file, useful for seeing control chars, etc and lines with no newline.

   od -c filename

4. Generate 512 bytes of random data, cat -ve escapes control chars.

   dd bs=1 count=512 if=/dev/urandom | cat -ve

5. list directory contents, display in 3 columns.

   ls | paste - - -

6. Loop through all files and perform an action on it.

   for na in * ; do echo $na ; done

7. Check for values in vars.

   [[ $(echo $var | grep -ic "pattern") -eq 0 ]] &

   You could also go for “-eq 1” – does contain or -ne 0 for same, etc. Plus you could use || for “or” either in place of “&&” or after this block – same as if .. then “positive” else “negative” fi.

8. Detach a process without it dying.

   disown [%1]

   nohup command > /tmp/logfile.log 2>&1&

   If you start a process with nohop (ignore the hup signal), it will not exist (usually) when your shell is exited. This can now be simulated on solaris, by backgrounding a process (with ctrl Z and bg) then typing disown. jobs command will show all backgrounded jobs. Ideally start commands like this, to avoid the shell exit problem:

9. Perform arithmetic in shell.

   bc -l

   Binary Calculator in long format – for float, etc. Can also be automated like this, to convert between decimal and hex:

   i=0; while ((i<20)) ; do echo -n "$i: "; echo "base=10;obase=16;$i" | bc; ((i++)); done | paste - - - -
0: 0 1: 1 2: 2 3: 3
4: 4 5: 5 6: 6 7: 7
8: 8 9: 9 10: A 11: B
12: C 13: D 14: E 15: F
16: 10 17: 11 18: 12 19: 13

[/example]

[reference]

[tags]Unix Shell Tips, Unix Shell Tricks, UNIX Arithmetic, Optical Dump, Unix Coding School[/tags]

• Linux Man Pages – bc command
• [ Linux Man Page – od ]
• [ Linux Man Page – dd ]
• [ Linux Man Page – ls ]
• [ Linux Man Page – bash ]

[/reference]

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