[SOLVED] if [something] then ignore this if and go straight

Sbrizzu · 01-16-2012, 02:30 PM

I'm writing a bash script and I need to know something, there is a command for this?:

Code:

if [ -e "something" ]
then
skip this if and go up with the code
else
mkdir "something"
go up with the code
fi

...other code...

Thank you!

T3RM1NVT0R · 01-16-2012, 02:42 PM

Hi Sbrizzu,

You are writing a bash script. I am unable to understand why you want to skip the first. I mean here is the syntax for if statement:

Code:

if [condition]
then
     execute
     execute
     execute
else
     execute
     execute
     execute
fi

From the post as I can understand you want that if the condition matches then do not execute the if part rather execute the else part. Any particular reason?

If you could let us know for which thing you are writing the script. What is the objective and what is the outcome that your expecting then it will be easy to guide you on that.

colucix · 01-16-2012, 02:51 PM

The answer to your question is the null command, that is a colon, e.g.

Code:

if [[ -d something ]]
then
  :
else
  mkdir something
fi

but you can easily invert the logic using the not operator, that is an exclamation mark:

Code:

if [[ ! -d something ]]
then
  mkdir something
fi

Moreover, in this specific example (testing if something exists and is a directory, see -d) you can simply do

Code:

mkdir -p something

without the if/then construct, since the -p option causes mkdir to silently skip the creation of an existing directory. HTH.

Sbrizzu · 01-16-2012, 02:52 PM

Ok, well, this script is intended to download each day a file from a site, and then put that file in folder, wich name's like "Monday 16", and that folder is in another folder, like "January 2012".
Some lines of code are better than words, so here it is that part, I want to substitute "continue" with a command that simply let me to skip the whole if and go straight:

Code:

datamonth=$(date +'%Y %B')
    dataday=$(date +'%A %d')
if [ -e ~/MyBook/Edizioni/"${datamonth}" ]
then
continue
else
mkdir ~/MyBook/Edizioni/"${datamonth}"
fi

if [ -e ~/MyBook/Edizioni/"${datamonth}"/"${dataday}" ]
then 
continue
else
mkdir ~/MyBook/Edizioni/"${datamonth}"/"${dataday}"
fi

Sbrizzu · 01-16-2012, 02:54 PM

Quote:

Originally Posted by colucix

The answer to your question is the null command, that is a colon, e.g.

Code:

if [[ -d something ]]
then
  :
else
  mkdir something
fi

but you can easily invert the logic using the not operator, that is an exclamation mark:

Code:

if [[ ! -d something ]]
then
  mkdir something
fi

Moreover, in this specific example (testing if something exists and is a directory, see -d) you can simply do

Code:

mkdir -p something

without the if/then construct, since the -p option causes mkdir to silently skip the creation of an existing directory. HTH.

Thank you! That's exactly what I mean!

David the H. · 01-16-2012, 02:56 PM

Please use [code][/code] tags around your code and data, to preserve formatting and to improve readability. Please do not use quote tags, colors, or other fancy formatting.

The basic logic seems clear to me. If the file doesn't exist, he has to go through some steps to create it first, or whatever. He's just a bit unclear on how to implement it.

To reverse the outcome of a test, use a "!".

Code:

if [ ! -e file ] ; do
	touch file
done

Another option is to run the ":/true" command, which means basically to do nothing.

Code:

if [ -e file ] ; do
	:
else
	touch file
done

BTW, you can use "!" to invert the exit status of any command.

Code:

if ! grep -q "line" file ; do

Edit: Darnit! Take a few minutes to type everything up cleanly and get scooped by another poster.

Sbrizzu · 01-16-2012, 03:01 PM

Since I'm here, can I ask another related question?
If I want to do that:

Code:

if [[ -e something/* ]]
then
rm -r something/*
execute the code in "else"
else
if you don't find it, simply skip the "rm -r" command 
...code...

David the H. · 01-16-2012, 03:09 PM

No. I don't believe globs expand in tests like that. And even if they did, it would expand to all the filenames in the directory, and look something like this:

Code:

if [[ -e something/file1 something/file2 something/file3 ]]

...which would result in a syntax error. Globs only work inside [[..]] when doing string comparisons.

If you want to determine whether a directory is empty, see here:

http://mywiki.wooledge.org/BashFAQ/004

T3RM1NVT0R · 01-16-2012, 03:10 PM

Let me get it straight. Your script will download a file everyday. Later in your script you want that it should scan if month directory exists or not. So you basically want to scan /MyBook/Edizioni/ to see if that month folder exist or not if it does exist then it should skip rest of the code and directly come to creation of Date folder under month folder. If it does not exist then it should create a month folder and then go for creating date folder and then copy the file.

I think the following script should do:

Code:

ls -l /MyBook/Edizioni/"${datamonth}" 2> /dev/null

if [ $? = 0 ]
then
          ls -l /MyBook/Edizioni/"${datamonth}"/"${dataday}" 2> /dev/null
          if [ $? = 0 ]
          then
               cp downloaded_file /MyBook/Edizioni/"${datamonth}"/"${dataday}" 
          else
               mkdir ~/MyBook/Edizioni/"${datamonth}"/"${dataday}"
               cp downloaded_file /MyBook/Edizioni/"${datamonth}"/"${dataday}"
          fi
else
          mkdir ~/MyBook/Edizioni/"${datamonth}"
          mkdir ~/MyBook/Edizioni/"${datamonth}"/"${dataday}"
          cp downloaded_file /MyBook/Edizioni/"${datamonth}"/"${dataday}"
fi

Sbrizzu · 01-16-2012, 03:15 PM

Quote:

Originally Posted by T3RM1NVT0R

Let me get it straight. Your script will download a file everyday. Later in your script you want that it should scan if month directory exists or not. So you basically want to scan /MyBook/Edizioni/ to see if that month folder exist or not if it does exist then it should skip rest of the code and directly come to creation of Date folder under month folder. If it does not exist then it should create a month folder and then go for creating date folder and then copy the file.

I think the following script should do:

Code:

ls -l /MyBook/Edizioni/"${datamonth}" 2> /dev/null

if [ $? = 0 ]
then
          ls -l /MyBook/Edizioni/"${datamonth}"/"${dataday}" 2> /dev/null
          if [ $? = 0 ]
          then
               cp downloaded_file /MyBook/Edizioni/"${datamonth}"/"${dataday}" 
          else
               mkdir ~/MyBook/Edizioni/"${datamonth}"/"${dataday}"
               cp downloaded_file /MyBook/Edizioni/"${datamonth}"/"${dataday}"
          fi
else
          mkdir ~/MyBook/Edizioni/"${datamonth}"
          mkdir ~/MyBook/Edizioni/"${datamonth}"/"${dataday}"
          cp downloaded_file /MyBook/Edizioni/"${datamonth}"/"${dataday}"
fi

Oh yes, if the download process was so simple maybe, the problem is that I have to work on files to obtain the link, and the code is, although not very long, quite long, and I wget directly in the right folder. I can simply copy-paste the download code in the else statement, and that's probably what I'm going to do.

Sbrizzu · 01-16-2012, 03:17 PM

I simply deleted the if, as it was not necessary

T3RM1NVT0R · 01-16-2012, 03:21 PM

I think that will be easier. Instead of cp then you can cd to the directory and then execute wget.

Sbrizzu · 01-16-2012, 03:21 PM

Ok, last edit, I managed like this, and it works:

Code:

if [[ -e ~/MyBook/Files/* ]]
then 
rm ~/MyBook/Files/*
else 
:
fi

Sbrizzu · 01-16-2012, 03:23 PM

Quote:

Originally Posted by T3RM1NVT0R

I think that will be easier. Instead of cp then you can cd to the directory and then execute wget.

There is a wget option to do this instead of cd, is more simple, it's

Code:

-P

T3RM1NVT0R · 01-16-2012, 03:26 PM

That will work as well :-)