Array lost its values??

hehe2046

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Oct 12, 2012, 4:41:58 AM10/12/12

to

$ unzip -qq -l test.zip
0 10-12-2012 14:23 a
0 10-12-2012 14:23 aa
0 10-12-2012 14:23 aaa
0 10-12-2012 14:23 b
0 10-12-2012 14:23 bb
0 10-12-2012 14:23 bbb
0 10-12-2012 14:23 c
0 10-12-2012 14:23 cc
0 10-12-2012 14:23 ccc

My scripts:

$ cat a.sh
#! /bin/bash
zipfile=$1
pattern=$2
i=0
unzip -qq -l ${zipfile} | grep ${pattern} | while read a b c d
do
i=$((i+1))
X[$i]="${d}"
echo "$i) ${X[$i]}"
done
echo "X[*] = \"${X[*]}\""

$ a.sh test.zip a
1) a
2) aa
3) aaa
X[*] = ""

I expected it should be:
1) a
2) aa
3) aaa
X[*] = "a aa aaa"

another script b.sh:
#! /bin/bash
i=0
for k in a b c d; do
i=$((i+1))
X[$i]="${k}"
echo "$i) ${X[$k]}"
done
echo "X[*] = \"${X[*]}\""

$ ./b.sh
1) a
2) b
3) c
4) d
X[*] = "a b c d" <==== this is expected

Why array X lost its values in script a.sh?

my bash version:
GNU bash, version 4.2.37(1)-release (i686-redhat-linux-gnu)
Copyright (C) 2011 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>

This is free software; you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Thanks

Janis Papanagnou

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Oct 12, 2012, 7:18:51 AM10/12/12

to

I see all the values. What is your problem?

You may be puzzled about the results of ${X[*]} ?
The use "${X[@]}". Try...

printf "'%s'\n" "${X[*]}"
printf "'%s'\n" "${X[@]}"

Janis

Lem Novantotto

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Oct 12, 2012, 7:46:48 AM10/12/12

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hehe2046 ha scritto:

> unzip -qq -l ${zipfile} | grep ${pattern} | while read a b c d

When you have pipes, you have subshells: each command in a pipeline is
executed as a separate process (i.e., in a subshell).

So you're setting an array in a subshell, and then you want it printed
out in a parent shell. No good. See:

$ echo readme | while read a ; do echo $a ; done ; echo $a
readme

$
--
Bye, Lem
Ceterum censeo ISLAM esse delendum
_________________________________________________________________
Non sprecare i cicli idle della tua CPU, né quelli della tua GPU.
http://www.worldcommunitygrid.org/index.jsp
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http://www.gpugrid.net/

Janis Papanagnou

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Oct 12, 2012, 8:16:52 AM10/12/12

to

On 12.10.2012 13:46, Lem Novantotto wrote:
> hehe2046 ha scritto:
>
>> unzip -qq -l ${zipfile} | grep ${pattern} | while read a b c d
>
> When you have pipes, you have subshells: each command in a pipeline is
> executed as a separate process (i.e., in a subshell).

And one solution for that issue could be

while read a b c d

do
...
done < <( unzip -qq -l "${zipfile}" | grep "${pattern}" )

so that the while loop is not executed in a subshell.

Janis

Janis Papanagnou

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Oct 12, 2012, 8:19:54 AM10/12/12

to

On 12.10.2012 13:18, Janis Papanagnou wrote:
> On 12.10.2012 10:41, hehe2046 wrote:

>> [...]

>> My scripts:
>>
>> $ cat a.sh

(I completely missed script a.sh - doh!)

>> [...]
>>
>> another script b.sh:
>> [...]

>> Why array X lost its values in script a.sh?

See Lem's explanation and my followup to his posting.

Janis

> [...]

Ben Bacarisse

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Oct 12, 2012, 9:29:06 AM10/12/12

to

hehe2046 <jjerr...@gmail.com> writes:

> $ unzip -qq -l test.zip
> 0 10-12-2012 14:23 a
> 0 10-12-2012 14:23 aa
> 0 10-12-2012 14:23 aaa
> 0 10-12-2012 14:23 b
> 0 10-12-2012 14:23 bb
> 0 10-12-2012 14:23 bbb
> 0 10-12-2012 14:23 c
> 0 10-12-2012 14:23 cc
> 0 10-12-2012 14:23 ccc
>
>
> My scripts:
>
> $ cat a.sh
> #! /bin/bash
> zipfile=$1
> pattern=$2
> i=0
> unzip -qq -l ${zipfile} | grep ${pattern} | while read a b c d
> do
> i=$((i+1))
> X[$i]="${d}"
> echo "$i) ${X[$i]}"
> done
> echo "X[*] = \"${X[*]}\""

The problem's been explained, but here's another possible solution:

X=($(unzip -qq -l "$1" | awk '$4 ~ /'"$2"'/ {print $4}'))

<snip>
--
Ben.

Lem Novantotto

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Oct 12, 2012, 2:18:49 PM10/12/12

to

Janis Papanagnou ha scritto:

> And one solution for that issue could be
>
> while read a b c d do
> ...
> done < <( unzip -qq -l "${zipfile}" | grep "${pattern}" )
>
> so that the while loop is not executed in a subshell.

Sure. :)

Just for the sake of curiosity, using ksh another solution could be a
coprocess ("|&").
For example:

$ print -e "a\naa\naaa" | grep -o "a*" |&
[1] 14777
$ unset X
[1] + Done print -e "a\naa\naaa" | grep -o "a*" |&
$ while read -p x; do print ${x}yes; X+=( $x ); done; echo ${X[*]}
ayes
aayes
aaayes
a aa aaa

hehe2046

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Oct 17, 2012, 11:46:00 PM10/17/12

to

Lem is right on this!

If I change to KSH, my a.sh works fine.
$cat a.sh
$! /bin/ksh

zipfile=$1
pattern=$2
i=0
unzip -qq -l ${zipfile} | grep ${pattern} | while read a b c d
do
i=$((i+1))
X[$i]="${d}"
echo "$i) ${X[$i]}"
done
echo "X[*]= \"${X[*]}\""

printf "%s\n" "${X[*]}"

echo "--"

printf "%s\n" "${X[@]}"

$./a.sh test.zip a
$ ./a.sh test.zip a

1) a
2) aa
3) aaa

X[*]= "a aa aaa"
a aa aaa
--
a
aa
aaa

For the pipeline, it is difference between bash and ksh

in ksh manual:
"Each command, except possibly the last, is run as a separate process;

while in bash manual:
"Each command in a pipeline is executed as a separate process (i.e., in a subshell)." as Lem pasted.

So my a.sh works find in ksh because the while doesn't run in subshell.
Then I add ps -e f in my script to approve this:

$ cat a.sh
#! /bin/ksh

zipfile=$1
pattern=$2
i=0
unzip -qq -l ${zipfile} | grep ${pattern} | while read a b c d
do

ps -e f
sleep 3

i=$((i+1))
X[$i]="${d}"
echo "$i) ${X[$i]}"
done
echo "X[*]= \"${X[*]}\""

printf "%s\n" "${X[*]}"

echo "--"

printf "%s\n" "${X[@]}"

$ ./a.sh test.zip a

4308 pts/2 Ss 0:00 \_ bash
7230 pts/2 S+ 0:00 | \_ /bin/ksh ./a.sh test.zip a
7235 pts/2 R+ 0:00 | \_ ps -e f

If I changed ksh to bash, I got:

4308 pts/2 Ss 0:00 \_ bash
7261 pts/2 S+ 0:00 | \_ /bin/bash ./a.sh test.zip a
7264 pts/2 S+ 0:00 | \_ /bin/bash ./a.sh test.zip a
7265 pts/2 R+ 0:00 | \_ ps -e f

Thanks everyone for the reply.
hehe2046

--http://compgroups.net/comp.unix.shell/array-lost-its-values/1949314