A question of "bad substition".

[sunburnt]

I haven`t quite figured out what Bash likes or doesn`t like and why.

Examples:

Code: Select all

# This works ( notice compound "Len=" statenment ):
Str=123A456 ; First=${Str:0:1} ; Len=$((${#Str}-1)) ; Last=${Str:$Len:1}
echo -e '\n### First letter:  '$First'   \n### Last letter:  '$Last

# And this:
S='1 2 3'
S="${S//[^ ]/}"; echo ${#S}

# But this errors:
S='1 2 3'
echo ${#${S//[^ ]/}}

The string length can go inside a math evaluation.
But a string length can`t have a replacement in it.

[technosaurus]

you can't "nest" substring manipulations

[big_bass]

Hey sunburnt

I think you missed the idea
I was trying to project in your other thread about awk

this is very easy using arrays
code readabilty is a factor to when you have to keep
track of large files with multiple searches of unique data

# But this errors:
S='1 2 3'
echo ${#${S//[^ ]/}}

your string now has spaces perfect for arrays now


this is what I used as an example in the other thread

# cat a file into an array
arr=(`cat /etc/rc.d/PUPSTATE`)

#get the string length of each array
echo ${#arr[0]}
echo ${#arr[1]}
echo ${#arr[2]}
echo ${#arr[3]}

# get each array
echo ${arr[0]}
echo ${arr[1]}
echo ${arr[2]}
echo ${arr[3]}

this is using your data getting the string length and
each variable *note all are ones because its only one character long

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Str="1 2 3"
# cat a file into an array
arr=($Str)

#get the string length of each array
echo ${#arr[0]}
echo ${#arr[1]}
echo ${#arr[2]}
echo ${#arr[3]}

# get each array
echo ${arr[0]}
echo ${arr[1]}
echo ${arr[2]}
echo ${arr[3]}

[sunburnt]

big_bass; I knew about filling arrays from a literal string, a variable, and a file.
But I didn`t think about using the Len code in getting the array item`s lengths.

technosaurus; Yeah... And it appears Bash code only works with a variable
in the first position ( hense the "$(" ), but will use literals for the rest.

[big_bass]

I know that you know about arrays
but they are also very useful when doing loops on data
they are very fast this feature is often overlooked
for pure POSIX solutions

bash 4 has even more power with arrays
and you have a complete tool


this is easier

Code: Select all

S=(1 2 3)

# get each array 
echo ${S[0]}
echo ${S[1]}
echo ${S[2]}

#get the string length of each array 
echo ${#S[0]}
echo ${#S[1]}
echo ${#S[2]}

==================================
*this one will surprise you with the output*
==================================

Code: Select all

s="alphaBETA"
echo ${s^^}     
echo ${s,,}     
echo ${s^}    

[sunburnt]

Yep, I like Bash`s ability to work equally well with variables, arrays, and files.
Some of the exec. files insist on using files though. Very old school...

Arrays do a great job of tracking lines by number (index).
But they`re the same as a variable list when doing string searches.
Which is most of the time, only rarely am I forced to use line numbers.

A web page about Bash4`s new features showed associative arrays, very good!
Great for translating characters and words, and very fast at it also.


So far "disktype" is the only thing that gives an unmounted partition`s format.
And parsing it is string search territory, I wish exec commands gave raw data.
But that`s the purpose of "sysinfo". I still need to add file info to it.

[technosaurus]

There is also guessfstype and blkid(full version or if enabled in busybox - see recent post on Barry's blog)

[sunburnt]

Thanks technosaurus; I`d tried blkid long ago, and it`s slower than disktype.
I`ve never heard of guessfstype, but Puppy doesn`t have it, and I can`t find it.

Fortunately the function "partinfo" is for human eyes, so slowness is okay.
I`ll just leave the function library code the way it is.

[Karl Godt]

guessfstype
should be a very important binary in Puppy ; BUT it might be named

~ # guess_fstype /dev/hda1
ext2

The only disadvantage of guess_fstype might be , that it seems not to work on 259er Major blkdrives kernels .

[sunburnt]

Karl Godt; You`re right, it is called: guess_fstype .

I`ll take a look at using it as it`s fairly fast.

Thanks... Terry B.