Bash Scripting

The discussion section on braces and parentheses was something I have over looked in the past, now its something to add to my bash skillZ.

I ran into the same thing with the tail +2 command. Unless you setup the _POSIX2_VERSION variable, the command didn't work on RHEL 5.6 but would work with on Solaris 10 x86

Was told that although >& will work (in Bash), the old school 2>&1 is better for compatibility. I do like the >& shortcut though.

I never knew about putting a 'tee' in a named pipe before either, that was nice.

I have already started modifying my scripts to use the $( ) instead of backticks. Much better, and easier to read.

Overall some good tips and a little info I might never use (noclobber?). But it's handy to have available.

I'm late to the party!

I've been doing shell scripting for a while now, but I learned a lot of stuff from this chapter -

for instance, the fact that { } and also ( ) will group commands together so you can redirect to a single file - the braces have a few more quirks though, with the whitespace requirement and the trailing semicolon. That will come in useful in some scripts I'm writing.

Also, I was always confused by the $( ) as a substitute for backticks. I prefer the look of $( ) to the backticks, but I understand that the backticks provide more backwards compatibility.

'tee' is awesome for logging... I use tee -a to append to logfiles when I want both stdout and stderr redirect, while still showing output on the screen. Helpful when you're sitting in front of a terminal running a script but you still want logging so you don't have to put a thousand 'sleep' commands in there so you can catch up ;-)

These are the things I learned that surprised me

ls formatting depends on whether its output is going to the terminal or a file.

contents 1> out 2> err
contents > out 2> err
contents >& out+err
contents >> appended

() runs in a subshell

using pipes causes commands to run in subshells

tee duplicates output : ... uniq | tee /tmp/x.x | awk -f transform.awk ...

$() uses output of subshell as a string

e.g. rm $(find . -name '*.rb')

equivalent to backticks ``

I read only whatever the O'Reilly preview allowed - which is not very less since only a few pages seem to have been skipped. In particular, I could not read 2.4,5,10,11,12,17,18,22 parts. However, I can guess they are about "echo -n", ">>", head, tail, xargs, and ">!". Am I correct? :)

The 'type' command and the swapping of STDOUT and STDERR were new and very useful to me.

I'm planning to get an ebook version of this book soon.

All done... (better late then never). The crazy file redirection was new to me e.g. 3>&1 1>&2 2>&3.

i skipped 2.18 but did the rest of the questions.

I couldn't get 2.12 to work, Skipping a Header in a File. tail kept trying to open the file '+2' and gave an error (see below).

I also skipped a couple towards the end like 2.19 and 2.20. The rest of the examples worked well, and I learned more than I expected to given it's the first chapter.