Bash variable recursion

Shell Programming and Scripting
1

Not sure how to ask this question. I want concatenate strings and variable recursively into new variable. For example:

infile01=/dir/subfolder/file01.txt
infile02=/dir/subfolder/file02.txt
infile03=/dir/subfolder/file03.txt
for i in {01..03}
do
u=${"infile"$i}
echo $u
done

I got error message:

-bash: ${"infile"$i}: bad substitution

How do I get output?

/dir/subfolder/file01.txt
/dir/subfolder/file02.txt
/dir/subfolder/file03.txt

Thanks a lot!

2

Whatever you are trying to do is a bad programming practice.

I would highly recommend using arrays instead which is pretty much straightforward:

infile[1]="/dir/subfolder/file01.txt"
infile[2]="/dir/subfolder/file02.txt"
infile[3]="/dir/subfolder/file03.txt"

for i in {1..3}
do
        echo "${infile[$i]}"
done
1 Like
3

Or, I tried:

for i in {01..03}
do
u=$"infile"$i
echo $u
done

and got

infile01
infile02
infile03

but I was expecting

/dir/subfolder/file01.txt
/dir/subfolder/file02.txt
/dir/subfolder/file03.txt

---------- Post updated at 05:58 PM ---------- Previous update was at 05:55 PM ----------

Thanks Yoda!
I should have thought of that way.

4

You can use eval to acheive it, but using it is a security risk and hence a bad programming practice.

infile01=/dir/subfolder/file01.txt
infile02=/dir/subfolder/file02.txt
infile03=/dir/subfolder/file03.txt
for i in {01..03}
do
        u=$( printf "infile%02d" "$i" )
        eval echo \$"$u"
done
5

You need to use eval....here is a simple example

[root@localhost cgi-bin]# x1="foo"
[root@localhost cgi-bin]# n=1
[root@localhost cgi-bin]# eval echo \${x$n}
foo
1 Like
6

A little perspective is in order.

Would you pass untrusted data to find . -exec $untrusted_data \; ? Or rm $untrusted_data ?

Simply using eval is not a security risk nor is it bad practice.

Trusting untrustworthy data is the real problem and it is bad practice regardless of the tool involved.

Regards,
Alister

7

Hi Yoda!
Another question not about the concatenation but related to the array index when it is "08". The problem is with 8 & 9 that caused problem as

 "bash: 08: value too great for base (error token is "08"). "

I am aware this is related to octal for 01~07 but not 08~09.. etc. I want this leading 0 for 1~9 for the filenames to be nicely aligned. What is the trick to include a leading zero to the number as array index, if any? Thanks a lot!

8

Use Associative Arrays:

#!/bin/bash

typeset -A infile

infile["01"]="/dir/subfolder/file01.txt"
infile["02"]="/dir/subfolder/file02.txt"
infile["03"]="/dir/subfolder/file03.txt"
infile["04"]="/dir/subfolder/file04.txt"
infile["05"]="/dir/subfolder/file05.txt"
infile["06"]="/dir/subfolder/file06.txt"
infile["07"]="/dir/subfolder/file07.txt"
infile["08"]="/dir/subfolder/file08.txt"
infile["09"]="/dir/subfolder/file09.txt"

for i in {01..09}
do
        echo ${infile["$i"]}
done