[SOLVED] BASH fancy test vs if statements how to?

BW-userx · 01-17-2017, 01:26 PM

@grail

I take it that the while is getting the path to read the FILENAME off of < <(find "$working_dir" -type f -name "*.mp3")

BW-userx · 01-17-2017, 01:28 PM

Quote:

Originally Posted by szboardstretcher

For the <<-EOF explanation:

http://man.cx/bash

Under the "Here Documents" section.

And for the set -- explanation:

http://man.cx/set

Search for -- in the page for information.

Thanks BOOKMARKED and checking them out.

szboardstretcher · 01-17-2017, 01:30 PM

Right on. The simple explanation for EOF not working is that linuxquestions copy/paste will convert TABS to SPACES. <<-EOF will only remove TABS.

You just have to either move EOF to the beginning of the line like this:

EOF

or put in TABS instead of SPACES in your favorite editor:

<TAB><TAB>EOF

BW-userx · 01-17-2017, 01:57 PM

Quote:

Originally Posted by szboardstretcher

Right on. The simple explanation for EOF not working is that linuxquestions copy/paste will convert TABS to SPACES. <<-EOF will only remove TABS.

You just have to either move EOF to the beginning of the line like this:

EOF

or put in TABS instead of SPACES in your favorite editor:

<TAB><TAB>EOF

fixed it by removing spaces and adding tabs, but it does not increment the counts or minus (does not do the math), nor does tabs move it off the left side of the terminal, which the later is not that big of a deal.

Code:

	cat <<-EOF

	MAX   is $max
	count is $((++count))
			  --------
		     $((max - count))

	EOF

szboardstretcher · 01-17-2017, 02:08 PM

I wouldnt put the increment inside a HEREDOC. Try something more like this untested psuedo example code:

Code:

count=0 #initialize outside of loop
while read -r line
do
 $((++count)) #increment outside HEREDOC, but inside loop
 cat <<-EOF
        count is $count
        EOF
done < file

BW-userx · 01-17-2017, 02:16 PM

Quote:

Originally Posted by szboardstretcher

I wouldnt put the increment inside a HEREDOC. Try something more like this untested psuedo example code:

Code:

count=0 #initialize outside of loop
while read -r line
do
 $((++count)) #increment outside HEREDOC, but inside loop
 cat <<-EOF
        count is $count
        EOF
done < file

Code:

In computing, a here document (here-document, here-text, heredoc, hereis, here-string or
here-script) is a file literal or input stream literal: it is a section of a source code
file that is treated as if it were a separate file.

this is workking fine though.

Code:

     echo "MAX    is $max"
     echo "count  is $((++count))"
     echo "           --------"
     echo "          $((max - count))"

MadeInGermany · 01-17-2017, 05:31 PM

One echo is more efficient than the cat << and the many echo

Code:

echo "
    MAX   is $max
    count is $((++count))
             --------
             $((max - count))

"

Because the echo string needs quotes, an embedded literal quote must be escaped.

BW-userx · 01-17-2017, 05:50 PM

Quote:

Originally Posted by MadeInGermany

One echo is more efficient than the cat << and the many echo

Code:

echo "
    MAX   is $max
    count is $((++count))
             --------
             $((max - count))

"

Because the echo string needs quotes, an embedded literal quote must be escaped.

Point taken .
thanks

grail · 01-17-2017, 08:55 PM

My apologies, I had not tested it and did not realise that the content would not increase or calculate

The echo is just as good, maybe better in this case, but as to the indenting, as mentioned by szboardstretcher, all tabs are removed, so if you need to indent something inside the heredoc when using
the -EOF version, you need to supply a space prior to the the indentation.

Code:

cat <<-EOF
<tab>First line
<tab><sp><tab>next line
EOF

The second line above would now effectively place 'next line' a tab distance from the edge.

BW-userx · 01-17-2017, 09:16 PM

Quote:

Originally Posted by grail

My apologies, I had not tested it and did not realise that the content would not increase or calculate

The echo is just as good, maybe better in this case, but as to the indenting, as mentioned by szboardstretcher, all tabs are removed, so if you need to indent something inside the heredoc when using
the -EOF version, you need to supply a space prior to the the indentation.

Code:

cat <<-EOF
<tab>First line
<tab><sp><tab>next line
EOF

The second line above would now effectively place 'next line' a tab distance from the edge.

yeah that worked, copy paste fails at times.

lol
I've never ventured into the meat of BASH. I was just sticking with what I leanred. pot shoting as you seen mixing different methoids. I just kept seeing others use that one liner and liked it. so I wanted to see if I could put it to use in this script.

Code:

[ true ] && do something (else) do something else

which equated to

Code:

[ true ] && do someting ; || do something else

then someone else in here pointed out that

Code:

mkdir -p

already test to see if it is there or not, so that widded it down even further to two lines of code for that code block I was using.

Now it is like amost nothing compaired to what I started out with. which was even less then the other scripts I wrote to deal with my mp3's.

I do enjoy changing that while loop getting rid of that pipe for sure.

Thanks to you and all of the others in this post, points given to everyone.

pan64 · 01-18-2017, 01:54 AM

Code:

if command1 then command2 else command3
# and
[ command1 ] && command2 || command3

are not the same, not equal to each other, you must not mix these two different constructs.

BW-userx · 01-18-2017, 07:45 AM

Quote:

Originally Posted by pan64

Code:

if command1 then command2 else command3
# and
[ command1 ] && command2 || command3

are not the same, not equal to each other, you must not mix these two different constructs.

construct

Code:

if true && do this ;  || (or) if not true do this
(true?do this:not true does this)
[true] && do this || not true does this
if true then do this else it is not true so do this instead

I do not know what you are talking about seeings how you did not define what you said to prove your theory that they are not the same.

it is no off - yes no logic

Ternary operator ( ?: ) in Bash is not supported per se'

Code:

(true?do this:not true does this)

so its equivalent is

Code:

[ variable = condition (which evaluates to a true statement) ] && value_if_true  || value_if_false

replaces if then else statements

Code:

if [ true ] ; then 
value_if_true
 else
value_if_false
fi

they are all the same.

Code:

variable = condition ? value_if_true : value_if_false

Ternary operator in bash

read this too
https://en.wikipedia.org/wiki/%3F:

pan64 · 01-18-2017, 08:11 AM

no, they are not the same. I have already tried to explain it here, on LQ, but here is it again (in short):
using if command1 then command2 else command2 the execution of command2 and command3 depends only on the result of command1
using [ command1 ] && command2 || command3 the execution of command3 may depend on both command1 and command2.
that is definitely a difference.

szboardstretcher · 01-18-2017, 08:30 AM

What pan is pointing out is this... They are not equal.

The && operator will fire off the command on the right if the exit code of the left was 0.

The || operator will fire off the command on the right if the exit code of the left was not 0.

For example:

Code:

true && echo "true" || echo "false"
outputs 'true' right?

true && false || echo "false"
outputs 'false'

So even though your first command is true, we can make the "OR" fire off. Which is wrong. That is not If, Then, Else. That is 'If command 1 exits zero, run command 2. If command 2 is non-zero, run command 3.'

In the simplest terms,. the || does not care about command1 at all. It only cares about command2.

BW-userx · 01-18-2017, 08:47 AM

Quote:

Originally Posted by szboardstretcher

What pan is pointing out is this... They are not equal.

The && operator will fire off the command on the right if the exit code of the left was 0.

The || operator will fire off the command on the right if the exit code of the left was not 0.

For example:

Code:

true && echo "true" || echo "false"
outputs 'true' right?

true && false || echo "false"
outputs 'false'

So even though your first command is true, we can make the "OR" fire off. Which is wrong. That is not If, Then, Else. That is 'If command 1 exits zero, run command 2. If command 2 is non-zero, run command 3.'

In the simplest terms,. the || does not care about command1 at all. It only cares about command2.

I like this argument, Now I got a whip out my editor and put away what I was doing. hold on,
let me put this to the test
I'll be back...