bash: why don't my "double if's" ever work?

L_Carver · 03-02-2017, 11:31 AM

Code as example:

Code:

comm1=$(exiftool -fast5  -s -S -Comment "$file0")
	if [[ $comm1 =  *"creator:gd-jpeg"* ]] || [[ $comm1 =  *"CREATOR:GD-JPEG"* ]] ; then
    		echo -e "$file0 has a \"libgd\" Comment. Writing to file."
			echo -e "$file0">>had-GD-comment.txt
			jhead -dc "$line"
			echo -e "Comment data removed from $file0."
			echo -e "$file0">>comment-cleared.txt
	fi

Two pipes between conditions in an if statement still means "or," doesn't it? Has the word "or" been totally worked out of bash 4? Anyway, when the script is run, and the conditions are met, it fails to create either text file in the above "if-then" to record which files did have JPEG comments with the gd-jpeg string (lower- or uppercase) in them.

And so I'm thinking I might be writing these "double ifs" incorrectly.

Any thoughts from the Peanut Gallery?

Carver

szboardstretcher · 03-02-2017, 11:37 AM

easy to check if your OR logic works, which it does:

Code:

#!/bin/bash -x
# type some jibberish, then some jibberish with string1 in it, then some jibberish with string2 in it
# works fine
read comm1
if [[ $comm1 =  *"string1"* ]] || [[ $comm1 =  *"string2"* ]] ; then
echo YES - i found either one string or the other
else
echo NO - i did not find either string
fi

So it must be something with your exiftool output.

Can you provide an example of what $comm1 is being set to before the comparison? ie:

Code:

comm1=$(exiftool -fast5  -s -S -Comment "$file0")
echo $comm1

c0wb0y · 03-02-2017, 12:40 PM

How about you try Bash's regex construct such as:

Code:

if [[ $comm1 =~  "string1" ]] ...

MadeInGermany · 03-02-2017, 03:03 PM

Posix-compliant is ==

Code:

if [[ $comm1 == *"string1"* ]] || [[ $comm1 == *"string2"* ]] ; then

The EREG allows a | or

Code:

if [[ $comm1 =~ "string1"|"string2" ]]
then
  ...
fi

Or the classic

Code:

case $comm1 in
(*"string1"*|*"string2"*)
  ...
;;
esac

is quite like the == glob style but further allows a | or.
But all this is more or less cosmetic. Your code works as intended.

nodir · 03-02-2017, 04:47 PM

Quote:

Originally Posted by MadeInGermany

Posix-compliant is ==

Code:

if [[ $comm1 == *"string1"* ]] || [[ $comm1 == *"string2"* ]] ; then

I don't think that = or == is Posix-compliant for pattern matching, one would use case instead.
And [ instead of [[ too, of course.
Perhaps i am wrong or you meant something different.

http://mywiki.wooledge.org/Bashism
(headline Conditionals)

MadeInGermany · 03-03-2017, 10:49 AM

You are right:
http://pubs.opengroup.org/onlinepubs/9699919799/
says:

Quote:

The KornShell-derived conditional command (double bracket [[]]) was removed from the shell command language description in an early proposal. Objections were raised that the real problem is misuse of the test command ([), and putting it into the shell is the wrong way to fix the problem. Instead, proper documentation and a new shell reserved word (!) are sufficient.

What a pity! The real problem is that [ ] requires additional quoting and X-ing and other ugly safety measures.

Shadow_7 · 03-03-2017, 01:10 PM

You need more quotes and less wild cards *O*. Just a guess, but normally solves my bash woes. I still find it difficult to read Bash as C has = to "SET" a value (always returns true) and == to "COMPARE" a value. These days speed of development matters more than speed of appliance, so I often dumb down my compares and make more of them.

Compare1 = ( "string1" = "string2" )
Compare2 = ( "string3" = "string4" )
OrCompare = 0;
if ( $Compare1 ); then OrCompare=1; fi
if ( $Compare2 ); then OrCompare=1; fi
if ( $OrCompare ); then
# actual useful stuff here;
fi

But I started early and breaking 80 columns was a crime. And debugging bash gets simpler this route too as you can check each condition based on VarNames in a single echo.

echo "DEBUG - C1: "$Compare1" - C2: "$Compare2" - OC: "$OrCompare