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Accepted
Aleksandar Ivanisevic
Asked: 2010-03-26 13:16:12 +0800 CST

skipping a variable using while read in bash

  • 772

i'm reading a few variables from a file using

while read a b c; do
  (something)
done < filename

is there an elegant way to skip a variable (read in an empty value), i.e. if I want a=1 b= c=3, what should I write in the file?

Right now i'm putting

1 "" 3

and then use

b=$(echo $b | tr -d \" )

but this is pretty cumbersome, IMHO

any ideas?

scripting bash shell

2 Answers

  1. Best Answer

    With a blank field:

    1 3

    You can do:

    if [[ -z c ]]
then
    c=b
    b=
fi

    If your data is comma delimited, you can also do:

    while IFS=, read a b c

    (but you'll have problems if your fields contain commas, as you may in your current version if they contain quotes):

    1,,3

    Also, in your version instead of using tr, you can do:

    b=${b//\"\"}

    but you can eliminate that step altogether using the following with your current data format:

    while IFS='"' read a b c

    however, comma-delimited fields is a more common format.

    • 3

  2. I am not sure if I understood what you want but you can skip certain values of the iteration (be it while, for or whatever) with continue and even stop the iteration with break

    while read a b c ;do 
   if [[ $b == 0 || $c == 0 || $a == 0 ]];then
      continue
   fi      
   (makelovenotwar)
done < /foo/bar
    • 0