How to use multiple variable susbtitution.

[Pawan Sangal]

Hi,

Please help in using multiple substitution with variable.
Below is the script Iam using in bash:

exc=/home/pawan/excep1

str1="pawan"
str2="arun"
str3="jagbir"
str4="sourin"
str5="ajay"
str6="makan"

for (( i=1; i <= 6; i++ ))
do
echo "${str$i}" >> ${exc}
done


But, Iam getting below error while trying:
excep2: line 13: ${str$i}: bad substitution

Please share if anybody have any idea to make this working.

Thanks in advance....


Pawan Sangal

[ghostdog74]

bash has arrays

exc=/home/pawan/excep1
str[0]="pawan"
str[1]="arun"
str[2]="jagbir"
str[3]="sourin"
str[4]="ajay"
str[5]="makan"
for (( i=0; i <= 5; i++ ))
do
echo "${str[i]}"
done

otherwise, if you really need to use that method, you can try eval
man eval for more info.

[wje_lf]

Pawan Sangal's script as of Thu Nov 1 02:08:33 PDT 2007:

exc=/home/pawan/excep1

str1="pawan"
str2="arun"
str3="jagbir"
str4="sourin"
str5="ajay"
str6="makan"

for (( i=1; i <= 6; i++ ))
do
echo "${str$i}" >> ${exc}
done

ghostdog74's's improved version as of Thu Nov 1 02:08:33 PDT 2007:

exc=/home/pawan/excep1
str[0]="pawan"
str[1]="arun"
str[2]="jagbir"
str[3]="sourin"
str[4]="ajay"
str[5]="makan"
for (( i=0; i <= 5; i++ ))
do
echo "${str[i]}"
done

Several suggestions for ghostdog's otherwise fine script:

Most importantly, of course, the output redirection must go back in:

exc=/home/pawan/excep1
str[0]="pawan"
str[1]="arun"
str[2]="jagbir"
str[3]="sourin"
str[4]="ajay"
str[5]="makan"
for (( i=0; i <= 5; i++ ))
do
echo "${str[i]}" >> ${exc}
done

Also, it's always a good idea to add this to the beginning of any bash script, if you're going to always run it under Linux (or elsewhere where bash is available):

#!/bin/bash

exc=/home/pawan/excep1
str[0]="pawan"
str[1]="arun"
str[2]="jagbir"
str[3]="sourin"
str[4]="ajay"
str[5]="makan"
for (( i=0; i <= 5; i++ ))
do
echo "${str[i]}" >> ${exc}
done

To make this code more maintainable, so that adding a new string won't require you to adjust the for statement:

#!/bin/bash

exc=/home/pawan/excep1
str[0]="pawan"
str[1]="arun"
str[2]="jagbir"
str[3]="sourin"
str[4]="ajay"
str[5]="makan"
for (( i=0; i < ${#str[@]}; i++ ))   # not <=
do
echo "${str[i]}" >> ${exc}
done

A little bit of care must be taken here.

${#str[@]}

does not mean the highest-used index plus one; it means the number of elements in the array, so

#!/bin/bash

exc=/home/pawan/excep1
str[0]="pawan"
str[1]="arun"
str[2]="jagbir"
str[3]="sourin"
str[4]="ajay"
str[6]="makan"
for (( i=0; i < ${#str[@]}; i++ ))
do
echo "${str[i]}" >> ${exc}
done

would cause the sixth line of output to be empty, not "makan".

[radoulov]

Or (assuming bash):

exc=/home/pawan/excep1

str1="pawan"
str2="arun"
str3="jagbir"
str4="sourin"
str5="ajay"
str6="makan"
set -- ${!str*}
set -- $(eval echo  \$str{1..$#})
printf "%s\n" "$@">"$exc"

Or the number of parameters is known, just:

printf "%s\n" $str{1..6}>"$exc"