Simple Bash script: What is wrong?

Question

I use Ubuntu Server as you can see:

#uname -a
Linux grosella 3.13.0-48-generic #80-Ubuntu SMP Thu Mar 12 11:16:15 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

Supose a data file like this (/tmp/data.txt):

1 AAAA
2 BBBB
3 CCCC
4 DDDD
5 EEEE
6 FFFF

Run the following Bash script:

typeset -i ACUM=0
typeset -a V=('')

cat /tmp/data.txt | \
while read LINEA ; do
  [ "x$LINEA" == "x" ] && break
  V=( $LINEA )
  VAL="${V[0]}"
  [ "x$VAL" == "x" ] && continue
  [[ $VAL =~ ^[0-9]+$ ]] || continue
  ((ACUM+=VAL))
  echo -e "VAL=$VAL\t\tACUM=$ACUM"
done

echo -e "\nFinal Result: $ACUM"

And here is the printed output:

VAL=1       ACUM=1
VAL=2       ACUM=3
VAL=3       ACUM=6
VAL=4       ACUM=10
VAL=5       ACUM=15
VAL=6       ACUM=21

Final Result: 0

Instead of 21, final result is 0. What is wrong?

Boo/hiss for not coming up with a better description of your problem before asking it. (See also http://stackoverflow.com/help/mcve) — Charles Duffy, May 04 '15 at 18:31

score 3 · Answer 1 · answered May 04 '15 at 18:28

3

When you pipe the data to your while loop that creates a subshell in which the while loop runs. The subshell cannot alter the environment variables of the parent, so the outer ACUM does not get changed.

answered May 04 '15 at 18:28

Eric Renouf

13,950
3
45
67

That's rigth! ... Thanks – abadjm May 04 '15 at 20:28

Cyrus · Accepted Answer · 2015-05-04T18:38:08.187

2

Change your code from

cat /tmp/data.txt | \
while read LINEA ; do
  # ...
done

to

while read LINEA ; do
  # ...
done < /tmp/data.txt

to avoid two subshells with its own environment.

edited May 04 '15 at 18:38

answered May 04 '15 at 18:30

Cyrus

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14
89
153

I did it ... For me, problem solved!! – abadjm May 04 '15 at 20:29

Simple Bash script: What is wrong?

2 Answers2